Article
Scube—Concept and Implementation of a Self-balancing, Autonomous Mobility Device for Personal Transport Manfred Klöppel 1,2, * , Felix Römer 1,2 , Michael Wittmann 2 , Bijan Hatam 2 , Thomas Herrmann 2 , Lee Leng Sim 3 , Jun Siang Douglas Lim 3 , Yunfan Lu 3 , Vladimir Medovy 2 , Lukas Merkle 2 , Wy Xin Richmond Ten 3 , Aybike Ongel 1 , Yan Jack Jeffrey Hong 3 , Heong Wah Ng 3 and Markus Lienkamp 2 1 2
3
*
TUMCREATE, 1 CREATE Way, #10-02, CREATE Tower, Singapore 138602, Singapore;
[email protected] (F.R.);
[email protected] (A.O.) Technical University Munich, Boltzmannstraße 15, 85748 Garching b. München, Germany;
[email protected] (M.W.);
[email protected] (B.H.);
[email protected] (T.H.);
[email protected] (V.M.);
[email protected] (L.M.);
[email protected] (M.L.) Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore;
[email protected] (L.L.S.);
[email protected] (J.S.D.L.);
[email protected] (Y.L.);
[email protected] (W.X.R.T.);
[email protected] (Y.J.J.H.);
[email protected] (H.W.N.) Correspondence:
[email protected]; Tel.: +49-89-289-10332
Received: 19 September 2018; Accepted: 20 November 2018; Published: 5 December 2018
Abstract: Public transportation (PT) systems suffer from disutility compared to private transportation due to the inability to provide passengers with a door-to-door service, referred to as the first/last mile problem. Personal mobility devices (PMDs) are thought to improve PT service quality by closing this first/last mile gap. However, current PMDs are generally driven manually by the rider and require a learning phase for safe vehicle operation. Additionally, most PMDs require a standing riding position and are not easily accessible to elderly people or persons with disabilities. In this paper, the concept of an autonomously operating mobility device is introduced. The visionary concept is designed as an on-demand transportation service which transports people for short to medium distances and increases the accessibility to public transport. The device is envisioned to be operated as a larger fleet and does not belong to an individual person. The vehicle features an electric powertrain and a one-axle self-balancing design with a small footprint. It provides one seat for a passenger and a tilt mechanism that is designed to improve the ride comfort and safety at horizontal curves. An affordable 3D-camera system is used for autonomous localization and navigation. For the evaluation and demonstration of the concept, a functional prototype is implemented. Keywords: autonomous vehicle; first/last mile; public transport; electric personal mobility device; on-demand; prototyping; localisation; 3D-camera navigation
1. Introduction 1.1. Motivation and State of Art Continuing urbanisation and the world’s growing population pose challenges to the provision of public services, economic opportunity, and maintenance of liveable spaces, particularly for megacities. In 2016, 25 megacities with a population of over 7 million people were housing 453 million people [1]. According to the United Nations [1], the proportion of the world’s population living in urban areas is expected to increase to 66% by 2050, while the number of megacities is projected to reach 42 by World Electric Vehicle Journal 2018, 9, 48; doi:10.3390/wevj9040048
www.mdpi.com/journal/wevj
World Electric Vehicle Journal 2018, 9, 48
World Electric Vehicle Journal 2018, 9, x FOR PEER REVIEW
2 of 15
2 of 15
2030. of 2030. the main of challenges increasing urbanisation traffic congestion duecongestion to the increased reachOne 42 by Onechallenges of the main of increasing isurbanisation is traffic due to demand for transportation. Policies promoting a modal shift from private cars to public the increased demand for transportation. Policies promoting a modal shift from privatetransportation cars to public (PT) have been (PT) a keyhave areabeen of interest not only to reduce externalities that are causedthat by the use of transportation a key area of interest not only to reduce externalities are caused private cars, however also to reduce the land that is devoted to private cars. However, PT systems by the use of private cars, however also to reduce the land that is devoted to private cars. However, often suffer from disutility being able to deliver userstoall the way from pointfrom of origin PT systems oftenthe suffer from of thenot disutility of not being able deliver users alltheir the way their to their destination. According to Polzin [2], people do not want to transfer modes unless necessary: point of origin to their destination. According to Polzin [2], people do not want to transfer modes the out-of-vehicle spent transferring perceived two orismore times more unfavourably unless necessary: time the out-of-vehicle time is spent transferring perceived two or more times than more in-vehicle travel time. Therefore, this first/last mile problem deters transit use even though a high PT unfavourably than in-vehicle travel time. Therefore, this first/last mile problem deters transit use service quality is provided for the majority of the ride distance. even though a high PT service quality is provided for the majority of the ride distance. Personal Personal mobility mobility devices devices (PMDs) (PMDs) which which have have recently recently entered enteredthe theroad roadtransport transportsystem systemcan can provide a solution to first/last mile problems when coupled with PT services. However, their usage provide a solution to first/last mile problems when coupled with PT services. However, their usage potential by their their safety safetyand andease easeofofuse. use.Most Most them require learning effort of potential has has been been limited limited by ofof them require learning effort of the the rider and require a standing riding position which makes riding difficult for elderly people or rider and require a standing riding position which makes riding difficult for elderly people or people people with disabilities. And even though PMDs folded, carryingthe thedevice deviceon on board board of with disabilities. And even though mostmost PMDs cancan be be folded, carrying of aa crowded bus or train can be difficult. PMDs with seats are also available, however rider comfort crowded bus or train can be difficult. PMDs with seats are also available, however rider comfortisis affected affectedby byroad roadinclinations. inclinations. PMDs PMDs with with aastanding standingriding riding position position allow allow the therider riderto tolean leaninto intothe the curve to compensate for the occurring centrifugal forces, while PMDs with a seat need to reduce speed curve to compensate for the occurring centrifugal forces, while PMDs with a seat need to reduce during turns toturns avoidtodiscomfort and theand toppling of the vehicle. ExistingExisting tilt mechanisms to reduce speed during avoid discomfort the toppling of the vehicle. tilt mechanisms to occurring forces from vehicle movement only react after an acceleration is sensed by the system which reduce occurring forces from vehicle movement only react after an acceleration is sensed by the results a latency between the occurrence theoccurrence forces andof thethe counter-measures of the system [3–6]. systeminwhich results in a latency betweenofthe forces and the counter-measures of Currently, most PMDs are controlled by the rider, however the introduction autonomous the system [3–6]. Currently, mostmanually PMDs are controlled manually by the rider,of however the capabilities could increase rider comfort and driving safety. introduction of autonomous capabilities could increase rider comfort and driving safety. PMDs are available in different form factors and technical implementations. The Segway PMDs are available in different form factors and technical implementations. ThePersonal Segway Transporter is an example a PMD on standing while riding. Figure 1a shows Personal Transporter is anofexample of awhich PMDthe on rider whichis the rider is standing while riding. Figurethe 1a Segway i2 which was introduced in 2006 [7]. The Segway weighs 47.3 kg and allows people to travel shows the Segway i2 which was introduced in 2006 [7]. The Segway weighs 47.3 kg and allows people at speedatofa up to 20 and withand a range up toof 39up kmto[8]. Figure pictures the Scewo a toatravel speed ofkm/h up to 20 km/h with of a range 39 km [8]. 1b Figure 1b pictures the Bro, Scewo self-balancing, electric electric wheelchair which provides a seat fora one is able to climb [9]. Bro, a self-balancing, wheelchair which provides seatperson for oneand person and is ablestairs to climb The vehicle weighs 120 kg and travels at 10 km/h with a range of 25 km. stairs [9]. The vehicle weighs 120 kg and travels at 10 km/h with a range of 25 km. The TheAirwheel Airwheel X8 X8isisshown shownin inFigure Figure1c. 1c. ItIt isis an anelectric electric unicycle unicycle where where the therider riderstands standsin inan an upright position and controls the speed and direction by the leaning of the body. Figure 1d shows upright position and controls the speed and direction by the leaning of the body. Figure 1d shows the theZoom ZoomStryder StryderEX EXelectric electricscooter scooterwhich whichisisfoldable. foldable.Both Boththe theAirwheel AirwheelX8 X8unicycle unicycleand andthe theZoom Zoom Stryder targeted forfor daily commuters whowho use use the devices to cover the last-mile StryderEX EXelectric electricscooter scooterare are targeted daily commuters the devices to cover the lastbetween their home theand station takeand the devices themwith ontothem trainsonto and trains buses. and Therefore, mile between their and home the and station take thewith devices buses. they are lightweight (11.1 kg; 10.7 kg) while the Airwheel X8 offers a travel speed of 18 km/h with of a Therefore, they are lightweight (11.1 kg; 10.7 kg) while the Airwheel X8 offers a travel speed range of 23 kma[10], and Zoom Stryder EXZoom offering a travel of 30 km/h speed and anofelectric range 18 km/h with range ofthe 23 km [10], and the Stryder EXspeed offering a travel 30 km/h and of approximately 30 km [11]. an electric range of approximately 30 km [11].
Figure1.1.Examples Examplesof ofvarious variousPMDs PMDs(Personal (Personalmobility mobilitydevices): devices): (a) (a) Segway Segway i2 i2 Personal Personal Transporter; Transporter; Figure (b)Scewo ScewoBro Bro[12]; [12];(c) (c)Airwheel AirwheelX8; X8;(d) (d)Zoom ZoomStryder StryderEX EX[11]. [11]. (b)
An personal mobility device is presented in [13]. TheThe basebase platform for Anexample exampleofofananautonomous autonomous personal mobility device is presented in [13]. platform their scooter is the S19 from Heartway Medical which canwhich carry one autonomous for their scooter is the S19 from Heartway Medical canseated carry passenger. one seatedThe passenger. The autonomous scooter uses two SICK LMS 151 LIDAR devices for navigation and obstacle recognition. The vehicle pose is estimated by the adoption of a Monte Carlo Localization (MCL) scheme after an
World Electric Vehicle Journal 2018, 9, 48
3 of 15
scooter uses two SICK LMS 151 LIDAR devices for navigation and obstacle recognition. The vehicle pose is estimated by the adoption of a Monte Carlo Localization (MCL) scheme after an initial manual mapping process of the environment [13]. LIDAR (light detection and ranging) systems offer a high resolution and long view range, however they require high computational power and are still expensive. 1.2. Problem Statement and Concept Description Based on the state of the art, different problems of current PMDs are identified. Available PMDs require manual control by the driver and, thus, require learning before the safe operation of the PMD is possible. Further, some PMD concepts require active body control and balancing of the user, e.g. the Airwheel X8, which makes control of the PMD more difficult and prevents the use by elderly or disabled persons. PMDs are already used for the first/last mile to reach PT, however bringing a PMD into a train or bus during peak hours is inconvenient due to the limited space, especially on days with precipitation when the PMD is wet and dirty. Larger sized PMDs offer space for seating, however they are even more inconvenient to bring into crowded PT systems. Further, while a seated position offers increased comfort, the passenger needs to shift their weight during turns to compensate for lateral forces. Current solutions which have been developed to counter lateral forces during turns can only react after sensing a force, reducing the effectiveness of the force compensation. To address the identified problems, we present an autonomous on-demand mobility device as a first/last mile solution which is developed to augment and improve the accessibility of existing public transport systems. The device does not belong to an individual person, however it is operated in a larger fleet. Passengers request a trip via a mobile application by entering their current location and the desired destination and then wait for pickup, omitting the need to carry the device on board of PT. The vehicle—dubbed Scube—is electrically driven, steers and navigates autonomously, and requires no control input by the passenger. A 3D-camera system in conjunction with local odometry is used for localisation to enable indoor-navigation. A camera-based system is used rather than a LIDAR device to reduce the costs. The vehicle features a seat for one person with no restraint system (e.g. seatbelt) for quick and easy accessibility. In order for the passengers to feel safe and comfortable during a ride on the device, a tilt-mechanism is developed to provide an active vehicle and passenger stabilisation. Contrary to state of the art solutions, the autonomous vehicle that is proposed in this paper determines the upcoming route itself and, therefore, can calculate the required tilt angles proactively. Further, the tilting allows the passenger to anticipate the path of the vehicle. A self-balancing vehicle design is chosen to maintain an upright sitting position for the passenger irrespective of the inclination of the road to increase rider comfort as well as to reduce the size and footprint of the vehicle. 2. Methodology After the introduction of the vehicle concept, a prototype of the vehicle was built. The primary purpose of the prototype was to demonstrate the general functionality of the concept. This section describes the design of the vehicle structure and tilt-mechanism of the computing system and the localisation system. 2.1. Ergonomic Design The dimensions of humans of the German population [14] and a study about the anthropometry of the Singaporean population [15] were taken into account for the ergonomic design of the vehicle. The respective body dimensions of a 5th-percentile Singaporean female and the 95th-percentile German male are shown in Figure 2 and were used to calculate the dimensions of the vehicle. The vehicle dimensions were further validated using the virtual manikins provided by the CATIA CAD software. The seating geometry is fixed and cannot be changed by the passenger.
World Electric Vehicle Journal 2018, 9, 48
4 of 15
World Electric Vehicle Journal 2018, 9, x FOR PEER REVIEW
4 of 15
Measurements in cm
13. Distance elbow—seat surface 14. Length of lower leg 16. Seat depth 21. Hip width sitting
Percentile Singapore Female 5%
German Male 95%
19.0
28.5
38.0 42.0 32.0
49.0 54.0 42.0
Figure Figure2.2.Body Bodymeasurements measurementsaccording accordingtotoreference reference[14,15]. [14,15].
2.1.1.Vehicle VehicleGeometry Geometry 2.1.1. Afterthe thedimensions dimensionsofofthe theergonomics ergonomicsofofthe thepassenger passengerseat seatare aredefined, defined,the theposition positionof ofthe the After wheel and the ground clearance were set. The device tilts forward and backwards during longitudinal wheel and the ground clearance were set. The device tilts forward and backwards during accelerationacceleration and deceleration. AccordingAccording to experiments conducted by Hatam al. [16], a slight longitudinal and deceleration. to experiments conducted byetHatam et al. [16], backward tilt is more comfortable for the passenger than a forward tilt for travel at a continuous speed. a slight backward tilt is more comfortable for the passenger than a forward tilt for travel at a Therefore, the wheel is placed directly the directly centre ofunder gravity of of thegravity passenger the continuous speed. Therefore, the wheel under is placed the(CG) centre (CG)with of the largest sizewith (95th-percentile German male) sitting on the vehicle. For smaller device passenger the largest size (95th-percentile German male) sitting on thepassengers, vehicle. Forthesmaller consequently tilts backwards as the CG of smaller sized people would move to the front of the vehicle. passengers, the device consequently tilts backwards as the CG of smaller sized people would move can be retracted to lower the vehicle for comfortable mounting by the passenger. to theThe frontwheels of the vehicle. When the wheels arebecompletely retracted, thevehicle devicefor rests on the flat mounting bottom surface increased The wheels can retracted to lower the comfortable by thefor passenger. stability. According to DIN 18040-1 [17], ramps in public spaces should have a maximum gradient When the wheels are completely retracted, the device rests on the flat bottom surface for increased ◦ of 6 per According cent or 3.43to. DIN The Singaporean Code on Accessibility the Built [18] states stability. 18040-1 [17], ramps in public spaces in should haveEnvironment a maximum gradient ofa ◦ for ramps with a vertical rise over 200 mm. Therefore, the maximum gradient of 8.3 per cent or 4.75 6 per cent or 3.43°. The Singaporean Code on Accessibility in the Built Environment [18] states a maximumgradient gradientoffor vehicle set tofor 5◦ .ramps The ground is set to200 70 mm results in maximum 8.3the per cent oris4.75° with a clearance vertical rise over mm.which Therefore, the ◦ an approach angle of which provides sufficient clearance, during acceleration. maximum gradient forapproximately the vehicle is 11 set to 5°. The ground clearance is set to even 70 mm which results in ◦ is achieved which enables Due to the short rear overhang, a departure angle of approximately 24 an approach angle of approximately 11° which provides sufficient clearance, even during high decelerations. acceleration. Due to the short rear overhang, a departure angle of approximately 24° is achieved
which enables high decelerations. 2.1.2. Suspension/Tilt Mechanism 2.1.2. Suspension/Tilt Mechanism The tilt mechanism of the vehicle is integrated into the suspension, as shown in Figure 3. Two independent linear actuators allow each wheel to be retracted and extended vertically. Each The tilt mechanism of the vehicle is integrated into the suspension, as shown in Figure 3. Two electric wheel hub motor is fixed to a mounting plate which is connected to the linear actuator. The independent linear actuators allow each wheel to be retracted and extended vertically. Each electric mounting plates are attached to the vehicle chassis with four slide bearings which are guided by two wheel hub motor is fixed to a mounting plate which is connected to the linear actuator. The mounting guide rails. plates are attached to the vehicle chassis with four slide bearings which are guided by two guide rails. For the dimensioning of the actuators, the abstract model of the vehicle that is shown in Figure 4 For the dimensioning of the actuators, the abstract model of the vehicle that is shown in Figure was used. For simplification, the mass of the vehicle and the passenger were summarised as a point 4 was used. For simplification, the mass of the vehicle and the passenger were summarised as a point mass m in the CG. The device has a track width t and is tilted by the angle Φ to the vertical axis. mass m in the CG. The device has a track width t and is tilted by the angle Φ to the vertical axis. To To tilt the device, both actuators move the same travel ∆st /2 in opposite directions. In this case, the tilt the device, both actuators move the same travel Δ𝑠 ⁄2 in opposite directions. In this case, the instantaneous centre of rotation M is at street level, centric between the wheels. The constant distance instantaneous centre of rotation M is at street level, centric between the wheels. The constant distance between the centre of rotation M and the CG is hCG . To fulfil the requirement that the passenger is free between the centre of rotation M and the CG is hCG . To fulfil the requirement that the passenger is free of lateral forces, the resultant force FR needs to point towards the centre of rotation M and is calculated of lateral forces, the resultant force FR needs to point towards the centre of rotation M and is calculated by the superposition of the centripetal force F and the weight force F . by the superposition of the centripetal force 𝐹C and the weight force 𝐹G .
World Electric Vehicle Journal 2018, 9, 48 World Electric Vehicle Journal 2018, 9, x FOR PEER REVIEW
5 of 15 5 of 15
World Electric Vehicle Journal 2018, 9, x FOR PEER REVIEW
5 of 15
Figure 3. 3. Display Display of of the the suspension suspension and and actuator actuator system. Figure
The static static force force F𝐹S,t per side calculated Figure 3. is Display of theas: suspension and actuator system. The , per side is calculated as: → ⃗ → ⃗ →⃗ 𝐹 𝐹 F𝐹 The static force 𝐹 , per side is calculated Fas: (1) G + FC , = R2 (1) Fs,t𝐹= 2 2 2 𝐹 ⃗ 𝐹⃗ 𝐹 ⃗ (1) 𝐹 , according to Equation 2 with the angular acceleration The dynamic forces 𝐹 , were calculated 2 2 The dynamic forces Facc,t were calculated according to Equation (2) with the angular acceleration Φ.. and the inertia 𝐽 described with the mass 𝑚 and ℎ : Φ and thedynamic inertia Jforces described thecalculated mass m and hCG : to Equation 2 with the angular acceleration were according The 𝐹 ,with 𝐽 Φ and the inertia 𝐽 described with the𝐹mass 𝑚 and ℎ 𝑚ℎ : (2) , ..Φ mh2CG J 𝑡.. Φ 𝑡 Φ Facc,t = ± Φ = ± (2) 𝐽 𝑚ℎ t actuator t (2) Φ Φ 𝐹 , and the extending actuator 𝐹 were The resulting total force for the retracting 𝐹 , 𝑡 𝑡, calculated as: The resulting total force for the retracting actuator Ft,r and the extending actuator Ft,e were The resulting total force for the retracting actuator 𝐹 , and the extending actuator 𝐹 , were calculated as: 𝐹, 𝐹, 𝐹 , (3) calculated as: Ft,r = Fs,t − Facc,t (3) 𝐹 𝐹 𝐹 (3) , , , 𝐹 𝐹 𝐹 (4) ,
,
Ft,e 𝐹 ,= Fs,t 𝐹 ,+ Facc,t 𝐹
,
,
(4) (4)
Figure 4. Abstract model of the vehicle for the calculations of occurring forces on the actuators. Figure 4. model of the calculations of forces onthe the vehicle), actuators. a track Figure 4. Abstract Abstracttotal model of the the vehicle for thekg calculations of occurring occurring on the actuators. With an assumed mass ofvehicle 155 kgfor (80 for the passenger, 75forces kg for width t of 0.49 m, a height ℎ of 0.7 m, and a maximum angular acceleration Φ of 50°/s2, a With an assumed total mass of 155 kg (80 kg for the passenger, 75 kg for the vehicle), a track .. maximum actuator force of 901 N was obtained. 2 , a maximum width m,m, a height hCG of andm, a maximum angular acceleration Φ of 50◦ /sΦ width ttofof0.49 0.49 a height ℎ 0.7ofm,0.7 and a maximum angular acceleration of 50°/s2, a Based on the calculations, two Thomson Electrak Pro linear actuators (PR2402-2A65) with Acme actuator force of 901force N was maximum actuator of obtained. 901 N was obtained. screw drives, 24 V electric motors, and 100 mm travel were chosen [19]. The linear actuators are Based on the calculations, two Thomson Electrak Pro linear actuators (PR2402-2A65) with Acme capable of carrying loads up to 1125 N and have a maximum speed of 50 mm/s. They are equipped screw drives, 24 V electric motors, and 100 mm travel were chosen [19]. The linear actuators are capable of carrying loads up to 1125 N and have a maximum speed of 50 mm/s. They are equipped
World Electric Vehicle Journal 2018, 9, 48
6 of 15
Based on the calculations, two Thomson Electrak Pro linear actuators (PR2402-2A65) with Acme screw drives, 24 V electric motors, and 100 mm travel were chosen [19]. The linear actuators are World Electric Vehicle Journal 2018, 9, x FOR PEER REVIEW 6 of 15 capable of carrying loads up to 1125 N and have a maximum speed of 50 mm/s. They are equipped with about the the position position of of the the actuator. actuator. with built-in built-in rotary rotary encoders encoders which which provide provide relative relative information information about The upper part of the actuators is fixed to the strut bearings, while the lower rods are connected The upper part of the actuators is fixed to the strut bearings, while the lower rods are connected to to the the wheel wheel mounting mounting plates. plates. This This enables enables the the relative relative motion motion between between the the wheel wheel and and the the frame frame when when the the actuator actuator is is operated. operated. The The self-locking self-locking actuators actuators with with Acme Acme screw screw drives drives were were chosen chosen to to prevent prevent unintended unintended lowering lowering of of the the device device when when the the actuators actuators are are not not powered. powered. 2.1.3. 2.1.3. System System Processing Processing Units Units The vehicle consists The vehicle consists of of one one main main computer computer and and several several micro-controllers micro-controllers to to control control different different functionalities of the vehicle. Figure 5 illustrates the connection diagram of the system components. functionalities of the vehicle. Figure 5 illustrates the connection diagram of the system components. The main processing processingunit unitisisthe the “UP-Board” [20]. microcomputer is equipped with anAtom Intel The main “UP-Board” [20]. ThisThis microcomputer is equipped with an Intel Atom X5 processor and 4 GB of RAM [20]. Ubuntu 16.10 is installed as the operating system, and X5 processor and 4 GB of RAM [20]. Ubuntu 16.10 is installed as the operating system, and the the “Libmraa” “Libmraa”library library[21] [21]isisused usedfor foraccess accessto tothe thehardware hardwareI/O. I/O.
Figure 5. 5. Overview of the system components. components.
Computationally intensive tasks of the the autonomous autonomous positioning, positioning, navigation, and control of of movement by by the the UP-Board. Directly connected to the UP-Board are the Intel movementwere wereprocessed processed UP-Board. Directly connected to the UP-Board are Realsense the Intel R200 3D-camera the ultrasound sensors, an Arduino Due microcontroller Realsense R200 [22], 3D-camera [22], thedistance-measuring ultrasound distance-measuring sensors, an[23] Arduino Due [23] for the control of the powertrain, an Arduino Leonardo [24] for the control of the linear actuators, microcontroller for the control of the powertrain, an Arduino Leonardo [24] for the control of the receiver of the wireless remote, a Wi-Fi access point the remote of the linear actuators, the receiver of and the wireless remote, and for a Wi-Fi access access point for the UP-Board. remote access of The long-term release “Kinetic Kame” of the open source meta-operating system Robot Operating the UP-Board. System [25] runs on the“Kinetic UP-BoardKame” to enable between the various functions The(ROS) long-term release of the the communication open source meta-operating system Robot and components the vehicle. Operating Systemof(ROS) [25] runs on the UP-Board to enable the communication between the various
functions and components of the vehicle. 2.1.4. Powertrain 2.1.4.Two Powertrain brushless-DC (BLDC) motors SYM-36-50ZE are selected for the powertrain of the vehicle [26]. The motors have a single-sided andSYM-36-50ZE a maximum torque outputfor of 28 with a nominal power Two brushless-DC (BLDC)shaft motors are selected theNm powertrain of the vehicle output of 500 W, whereas the peak power output reaches 700 W and enables a maximum vehicle speed [26]. The motors have a single-sided shaft and a maximum torque output of 28 Nm with a nominal of approximately The maximum current reaches is 25 A. 700 W and enables a maximum power output of 20 500km/h. W, whereas the peakrequired power output The vehicle is designed to have one electric motor on each The is motor vehicle speed of approximately 20 km/h. The maximum requiredside. current 25 A.controller RoboteQ FBL2360 was selected as it is a dual channel controller that supports BLDC machines and sinusoidal The vehicle is designed to have one electric motor on each side. The motor controller RoboteQ control of the motors [27]. Sinusoidal excitation is smoother and results in a quieter operation and a FBL2360 was selected as it is a dual channel controller that supports BLDC machines and sinusoidal more precise control as well as a higher efficiency due to less dissipation of heat. A serial connection control of the motors [27]. Sinusoidal excitation is smoother and results in a quieter operation and a allows sending commands data from inverter. The motor controller a more precise control as welland as a receiving higher efficiency duethe to less dissipation of heat. A serial supports connection continuous maximum current of 40 A, a voltage of 60 V per channel, and the recuperation of brake allows sending commands and receiving data from the inverter. The motor controller supports a energy. It canmaximum estimate the state of of charge of of the60battery uses the of the motor to continuous current 40 A, a(SOC) voltage V per and channel, andhall thesensors recuperation of brake provide odometry data.the state of charge (SOC) of the battery and uses the hall sensors of the motor energy. It can estimate A 36 V, 12s3p-battery to provide odometry data.pack with a capacity of 297 Wh was selected for the prototype. The cells were of theAtype ANR26650M1B LiFePO and support C-ratesfor upthe to 28 [28]. The The capacity 4 chemistry 36 V, 12s3p-battery with pack awith a capacity of 297 Wh was selected prototype. cells was sufficient for test drives of about 3 km with an average speed of 11.5 km/h. were of the type ANR26650M1B with a LiFePO4 chemistry and support C-rates up to 28 [28]. The capacity was sufficient for test drives of about 3 km with an average speed of 11.5 km/h. The control algorithm of the powertrain and self-balancing was executed on the Arduino Due and requires the lateral velocity of the vehicle and the balancing angle as inputs. Vehicle speed was obtained by the wheel odometry via the motor controller. The balancing angle was measured with
World Electric Vehicle Journal 2018, 9, 48
7 of 15
The control algorithm of the powertrain and self-balancing was executed on the Arduino Due and requires the lateral velocity of the vehicle and the balancing angle as inputs. Vehicle speed was obtained by the wheel odometry via the motor controller. The balancing angle was measured with an inertial measurement unit (IMU) of an Arduino 101 [29] which includes a gyroscope and an accelerometer. 2.2. Localisation Scube is equipped with various sensors to determine its location. While local positioning is used to measure the relative movement of the vehicle, global positioning determines the absolute position on a 2D-plane. The local positioning is conducted by in-vehicle odometry for dead reckoning and ultrasound-sensors and does not rely on external sources of information. The two wheels of Scube are arranged on a single axis with a differential steering system. The odometry relies on the revolution speed, the difference of the revolution speed of the two wheels, the wheel radius, and the distance between the two wheels, the so-called track-width. In the case of Scube, wheel revolutions are measured by the motor controller which evaluates the information of the hall sensors that are built into the motors. For the detection of objects in the near proximity of the vehicle, two rear- and two front-facing ultrasound-sensors of the type HC-SR04 are built into the Scube [30]. The sensors have a range of maximum 4 m and have a measuring angle of 15◦ . For the global positioning, a landmark-based approach with an Intel Realsense R200 3D-camera [22] was implemented. The Intel Realsense R200 camera is equipped with two infrared (IR) cameras to capture a 3D-image with a resolution of 640 × 480 pixels at a rate of 60 Hz. An additional RGB-camera provides a colour-image with a resolution of 1920 × 1080 pixels. The integrated IR-projector is designed for a range of up to 2.8 m, however longer ranges are possible with increased noise and inaccuracies. The camera is mounted on the front side of the vehicle below the footrest. The imaging algorithms are able to function despite the shift of the camera tilt during vehicle movement. Landmarks are any objects in the environment of which the global position is known [31]. For this experimental setup, QR-codes were used as landmarks. By recognising and measuring the distance to the landmarks, the position was calculated by trilateration. Trilateration requires three known points in space, however for the presented use case, the recognition of two points is sufficient for the positioning on a 2D-plane which results in two possible locations. Figure 6a illustrates how the correct location is determined by a logical check if the calculated location is within the perimeter of the map and by comparing the relative position of the two landmarks from the video stream of the camera. If more than two landmarks are visible to the camera at the same time, an algorithm decides which two landmarks are most suitable for positioning. The decision is based on the distance between the landmark and the vehicle as well as the distance between the landmarks to avoid unfavourable angles for 2D-trilateration. Besides the position, the heading of the vehicle is required. The orientation is calculated by using the pinhole-camera model [32] which is shown in Figure 6b. The heading is described by the angle α between the x-axis of the local coordinate system to the x-axis xG of the global coordinate system. The camera only returns the orthogonal distance to the plane of the focal point. With the → → specifications of the focal length and the camera image size, the distances PS1 and PS2 are determined. The landmarks S1 and S2 are projected to the plane of the camera image (S10 and S20 ) and →
→
are set in relation to the mid-point H’ of the camera image to determine S1 H, S2 H and the point H. →
The obtained vector PH represents the local x-axis of the vehicle and is used to calculate the vehicle heading α.
World Electric Vehicle Journal 2018, 9, 48 World World Electric Electric Vehicle Vehicle Journal Journal 2018, 2018, 9, 9, x x FOR FOR PEER PEER REVIEW REVIEW
8 of 15 88 of of 15 15
Figure Figure 6. 6. (a) (a) Localization Localization by by recognition recognition of of landmarks; landmarks; (b) (b) Calculation Calculation of of heading heading by by the the pinholepinholeFigure 6. (a) Localization by recognition of landmarks; (b) Calculation of heading by the camera model. camera model. pinhole-camera model.
3. Results Results 3. 3.1. Structure/Body 3.1. Structure/Body The load-bearing load-bearing structure of the device mainly made square aluminium profiles (Figure The square aluminium profiles (Figure 7). load-bearing structure structureof ofthe thedevice deviceisis ismainly mainlymade madeofof of square aluminium profiles (Figure 7). The profiles are joined in various positions and angles by connectors which can endure tensile The profiles are joined in various positions and angles by connectors which can endure tensile forces 7). The profiles are joined in various positions and angles by connectors which can endure tensile forces of up to kN [33]. The frame is of 40 ×× 40 mm and 30 mm aluminium profiles. of up to [33]. frame is made of 40 mm and 3030 profiles. forces of 10 upkN to 10 10 kN The [33].main The main main frame is made made of× 4040 40 mm and 30×××30 30 mm mm aluminium profiles. The strut bearings take the load of the actuator forces and are milled out of aluminium. The backrest The ofof aluminium. The backrest is The strut strut bearings bearingstake takethe theload loadofofthe theactuator actuatorforces forcesand andare aremilled milledout out aluminium. The backrest is made from a 12 mm aluminium rod to provide both strength and a curvature to increase the made from a 12 mm aluminium rod to provide both strength and a curvature to increase the comfort is made from a 12 mm aluminium rod to provide both strength and a curvature to increase the comfort of of the backrest. comfort of the the backrest. backrest. The outer vehicle is from 3D-printed parts with aa maximum thickness of The outer shellof the vehicle is made from 3D-printed a maximum thickness of outer shell shell ofofthe the vehicle is made made from 3D-printed partsparts withwith maximum thickness of 22 mm. mm. A hexagon reinforcement structure was incorporated into the 3D-printed parts to increase their 2Amm. A hexagon reinforcement structure was incorporated into the 3D-printed to increase hexagon reinforcement structure was incorporated into the 3D-printed parts parts to increase their stiffness. their stiffness. stiffness.
Figure Figure 7. 7. (a) (a) Mainframe Mainframe of of Scube; Scube; (b) (b) Scube Scube with with attached attached shell. shell.
Figure Figure 88 displays displays the the final final dimensions dimensions of of Scube. Scube. The The rigidity rigidity of of the the aluminium aluminium frame frame is is sufficient sufficient to carry a person, while the lowering mechanism allows for improved accessibility. When the to carry a person, while the lowering mechanism allows for improved accessibility. When the vehicle vehicle
World Electric Vehicle Journal 2018, 9, 48
World Electric Vehicle Journal 2018, 9, x FOR PEER REVIEW
9 of 15
9 of 15
Figure 8 displays the final dimensions of Scube. The rigidity of the aluminium frame is sufficient 9 of 15 to carry a person, while the lowering mechanism allows for improved accessibility. When the vehicle is in the lowered position, the whole bottom of the vehicle rests on the ground to provide a stable is in in the the lowered lowered position, position, the the whole whole bottom bottom of of the the vehicle vehicle rests rests on on the the ground ground to to provide provide aa stable stable is platform for ingress and egress that is comparable to a wheelchair. The reduction of the thickness of platform for ingress and egress that is comparable to a wheelchair. The reduction of the thickness of platform and egress that isfor comparable to aand wheelchair. The reduction of the thickness of the shell for to 2ingress mm reduced the costs 3D-printing, the hexagon structure provides sufficient the shell shell to 22 mm reduced the costs for 3D-printing, and the the hexagon structure provides provides sufficient the reduced costs forfenders. 3D-printing, and hexagon structure strength, to evenmm for the largerthe parts, e.g. The total weight of the prototype is 74 kg. sufficient strength, even even for for the the larger larger parts, fenders. The The total total weight weight of of the the prototype prototype is strength, parts, e.g. e.g. fenders. is 74 74 kg. kg. World Electric Vehicle Journal 2018, 9, x FOR PEER REVIEW
Figure 8. Exterior dimensions of the vehicle. Figure 8. Exterior Exterior dimensions dimensions of the vehicle.
3.2. Simulation of the Tilt Mechanism 3.2. Simulation Simulation of of the the Tilt Tilt Mechanism Mechanism 3.2. A multi-body simulation of the vehicle concept was conducted to evaluate the influence of the A multi-body multi-body of concept was to to evaluate influence of the tilt A simulation ofthe thevehicle vehicle concept wasconducted conducted evaluate of the tilt mechanism onsimulation driving behaviour. The multi-body simulation was set the upthe toinfluence determine the mechanism on driving behaviour. The multi-body simulation was set up to determine the maximum tilt mechanism on driving multi-body setwas up generated to determine maximum achievable lateralbehaviour. accelerationThe during a turn. Asimulation predefinedwas route withthe an achievable lateral acceleration during a turn. A predefined route was generated with an increasingly maximum achievable lateral (Figure acceleration during a turn. predefined route was generated with an increasingly reduced radius 9a). The vehicle wasAsimulated with a constant speed of 2 m/s. reduced radius (Figure 9a). The vehicle was simulated withsimulated a constant speed of 2 m/s. The simulation increasingly reduced radius (Figure 9a). The vehicle was with a constant speed ofor2 after m/s. The simulation was run until the vehicle started to deviate from the route due to slipping was run until the vehicle started to deviate from the route due to slipping or after tumbling. Figure 9b The simulation was run until the vehicle started to deviate from the route due to slipping or after tumbling. Figure 9b shows that the vehicle without the tilt mechanism enabled can reach a maximum shows that the vehicle without the tilt mechanism enabled can reach a maximum lateral acceleration 2 tumbling. Figure 9bof shows thatbefore the vehicle without tilt mechanism canof reach a maximum lateral acceleration 2.5 m/s toppling over.the Figure 9c displaysenabled the result the vehicle with 2 before toppling over. Figure 9c displays the result of the vehicle with the tilting enabled. of m/s 2 was lateral acceleration m/s2 before topplingofover. Figure 9cachieved displays without the result ofvehicle the vehicle with the2.5 tilting enabled. of A 2.5 maximum acceleration 6.8 m/s the tumbling 2 was achieved without the vehicle tumbling over. A maximum acceleration of 6.8 m/s the tilting enabled. A maximum acceleration of 6.8 m/s2 was achieved without the vehicle tumbling over. over.
Figure 9. 9. Simulation of occurred acceleration during a defined turn (a) without tilting (b) and with with tilting (c). Figure 9. Simulation of occurred acceleration during a defined turn (a) without tilting (b) and with tilting (c).
3.3. Vehicle Performance 3.3. Vehicle Performance 3.3. Vehicle Performance After acquiring map and location data, the vehicle waits for user input about the next destination. After acquiring map and location data, the vehicle waits for user input about the next OnceAfter the destination is entered a website-based user interface, from the current position andvia location data, vehicle waitsthe forpath user input destination.acquiring Once themap destination is entered viathe a website-based user interface, theabout path the fromnext the is calculatedOnce and the vehicle turnsis on the spot the directionuser of the first waypoint. After the destination. destination entered via into aon website-based interface, pathwaypoint. from the current position is the calculated and the vehicle turns the spot into the direction of the the first correct initial heading is reached, vehicle smoothly accelerates tothe a configurable driving speed and current position calculated andisthe the vehiclethe turns on the spot into direction the first waypoint. After the correctisinitial heading reached, vehicle smoothly accelerates to a of configurable driving After initial heading is reached, vehicle smoothly accelerates to a configurable driving speedthe andcorrect follows the pre-calculated path. the At the destination point, the vehicle is stopped and waits speed the pre-calculated path. At the destination point, the vehicle is stopped and waits for theand nextfollows destination input. for the next destination input.
World Electric Vehicle Journal 2018, 9, 48
10 of 15
follows the pre-calculated path. At the destination point, the vehicle is stopped and waits for the next destination input. If any obstacle is detected within approximately 0.5 m, the vehicle stops. After a waiting period, the vehicle starts to turn on the spot until it can pass the obstacle. If turning is not sufficient, the vehicle aborts the current route. During travel, the expected current position provided by the local odometry is constantly compared with the actual measurement by the global localisation system. If the difference increases to over 0.4 m, a recalibration is executed where the vehicle comes to a stop. In order to prevent an oscillating driving course, a heading deviation of +/− 0.2 rad (approximately +/− 11.5◦ ) is allowed. Autonomous navigation and driving were conducted in a test area of 12 m × 5 m with three different destinations. The vehicle speed in the autonomous mode is limited to 0.3 m/s due to safety measures. The maximum rotational speed is set to 0.5π rad/s. The minimum rotation speed is 0.6 rad/s in order to overcome initial rolling resistance. Within the test area, the vehicle was able to acquire its position by landmark recognition and responded to passenger transport requests. Obstacle detection (e.g. people standing in the pathway) proved to be successful. 3.4. Localisation Results The results of the localisation system are presented to demonstrate the achieved accuracy with the RealSense R200 camera system and the local odometry. The effect of the size of the QR-code is studied, then the accuracy of the global localisation is measured. Further, the accuracy of the vehicle odometry is tested with a pre-defined path. Finally, the results of an autonomously followed path are shown. The QR-codes that were utilised for landmark localisation were printed full-page on different paper sizes ranging from DIN A1 (594 mm × 841 mm) to DIN A4 (210 mm × 297 mm). Due to the limited resolution of the camera system of 640 × 480 pixels, identification and recognition of the landmarks are only possible within a certain range to the landmark depending on the size of the QR-code, as shown in Table 1. Landmarks printed in DIN A1 size are recognisable up to 7–8 m, while landmarks printed on DIN A4 can only be recognised up to 2 m. Table 1. Influence of QR-code landmark size on recognition distance. Size of QR-Code
Maximum Distance for Recognition
DIN A1 DIN A2 DIN A3 DIN A4
7–8 m 5–7 m 3–4 m 2m
Besides the recognition of the landmarks, the resulting accuracy of the localisation was measured and is shown in Figure 10. The setup that is displayed in Figure 10 contains five QR-code-landmarks which are aligned on the same plane and facing the same direction. The two outermost QR-code-landmarks (code 14 & code 15) have the size DIN A1, while the QR-code-landmarks in the middle (code 1, code 8, code 11) are printed in DIN A3 size. The distance between the landmarks and the vehicle was increased from 1 m to 4 m in 0.5 m increments. Two further measurement runs were conducted at a distance of 5 m and 6 m. The red crosses indicate the true position of the vehicle. At each position, 100 localisation runs were conducted (blue and green marks) by the vehicle. The black cross indicates the averaged measured position. The results in Figure 10 show that up to a distance of 2 m, the accuracy in both the x- and the y-axis is high, and the standard deviation in x- and y-direction is less than 2 cm and 1 cm, respectively. With increasing distance, the accuracy decreases. At a distance of 6 m, the standard deviation in the x-direction is 9 cm while it is 2 cm in the y-direction. Overall, the accuracy of the distance measurement (y-axis) is distinctively higher than the measurement in the x-direction because the distance is natively
World Electric Vehicle Journal 2018, 9, 48
11 of 15
World Electric Vehicle Journal 2018, 9, x FOR PEER REVIEW
11 of 15
measured by the 3D-camera, while the lateral position is calculated by triangulation and is more World Electric Vehicle Journal 2018, 9, x FOR PEER REVIEW 11 of 15 strongly influenced by measuring errors. Distance [m] Distance [m]
1.0
1.01.5 1.52.0 2.02.5 2.53.0 3.0 3.5 3.5 4.0 4.0 5.0 5.0 6.06.0
Average Standard deviation [m] deviation [m] Average Standard (x-axis / y-axis) (x-axis / y-axis) deviation [m] deviation [m] / 0.00 (x-axis 0.010 / 0.001 (x-axis0.01 / y-axis) / y-axis) / 0.04 0.010.02 / 0.00 0.010 0.020 / 0.001/ 0.004 0.020.02 / 0.04 0.020 0.020 / 0.004/ 0.004 / 0.02 0.020.10 / 0.02 0.020 / 0.004/ 0.010 / 0.01 0.040 0.100.11 / 0.01 0.040 / 0.010/ 0.010 / 0.02 0.030 0.11 / 0.02 0.030 / 0.010 0.21 / 0.02 0.070 / 0.010 0.21 / 0.02 0.070 / 0.010 0.19 / 0.06 0.080 / 0.010 0.19 / 0.06 0.080 / 0.010 0.10 / 0.18 0.090 / 0.010 0.10 / 0.18 0.090 / 0.010 0.22 / 0.22 0.22 / 0.22 0.090 0.090 / 0.020/ 0.020
Figure Distributionof oflocalisation localisation measurements using multiple landmarks. Figure 10.10. measurements using multiple landmarks. Figure 10. Distribution measurements using multiple landmarks.
The overall accuracy ofthe the localodometry odometry system was examined by by tracking the predefined The The overall overall accuracy accuracy of of the local local odometry system system was was examined examined by tracking tracking the the predefined predefined route shown in Figure 11a. The vehicle was manually moved on a 4 m × 4 m box-shaped route (black) route shown in Figure 11a. The vehicle was manually moved on a 4 m × 4 m box-shaped route (black) route shown in Figure 11a. The vehicle was manually moved on a 4 m × 4 m box-shaped and the data of the internal odometry is plotted (blue). Figure 11b shows the course of the measured and of the internal odometry is (blue). Figure 11b the course and the the data data In of the thefinal internal odometry is plotted plotted (blue). Figure 11bmshows shows course of of the the measured measured heading. position, a deviation of 0.1 m (x-axis) and 0.2 (y-axis)the is measured. The final heading. In the final position, a deviation of 0.1 m (x-axis) and 0.2 m (y-axis) is measured. The heading. position, deviation 0.1 m (x-axis) and 0.2 m (y-axis) is measured. The final final heading error is 0.037 rad, respectively 2.1°. ◦. heading heading error error is is 0.037 0.037 rad, rad, respectively respectively 2.1 2.1°.
Figure 11. (a) Comparison of the predefined driving route (black) with data recorded by onboard odometry (blue); (b) Recorded heading during travel over the predefined route.
Figure 11. (a) (a) Comparison of the the predefined predefined drivingdriving route (black) (black) with data dataFigure recorded by onboard Finally, the overall functionality of autonomous was evaluated. 12aby shows the Figure 11. Comparison of driving route with recorded onboard odometry (blue); (b) Recorded heading during travel over the predefined route. outline of the testing area withheading the dimensions of approximately 5 m × 12.5 m. For this evaluation, odometry (blue); (b) Recorded during travel over the predefined route. the initial position of Scube is measured (green cross) and a destination is transmitted to the vehicle Finally,cross). the overall overall functionality of autonomous driving was evaluated. 12acourse shows the the Finally, the functionality autonomous driving was evaluated. Figure 12a shows (orange The calculated track isof a straight line (black dotted line), which helps to detect deviations for this evaluation. Figure 12b displays enlarged view of the track the outline of the the testing testing area with with the thedimensions dimensions ofan approximately m××test outline of area of approximately 55m 12.5 m.and Forincludes this evaluation, waypoints (black calculated by(green the vehicle. theaavehicle follows calculatedto track, it the initial initial position ofcrosses) Scube is is measured (green cross)As and destination isthe transmitted to the vehicle vehicle the position of Scube measured cross) and destination is transmitted the continuously tracks its position (blue line). In the beginning, a course deviation can be seen, which is (orange cross). cross). The The calculated calculated track track is is aa straight straight line line (black (black dotted dotted line), line), which which helps helps to to detect detect course course (orange because of the intentionally allowed course tolerance to avoid an oscillating driving course. The track deviations for this enlarged view of of thethe testtest track andand includes the deviations this evaluation. evaluation.Figure Figure12b 12bdisplays displaysanan enlarged view track includes correction occurring at the position (2 m|3.5 m) is explained by a recalibration of the localisation waypoints (black crosses) calculated byby thethe vehicle. the waypoints (black crosses) calculated vehicle.AsAsthe thevehicle vehiclefollows followsthe the calculated calculated track, itit system after it detected a deviation between the positions provided by local odometry and the global continuously tracks its its position position (blue (blue line). line). In In the the beginning, beginning, aa course course deviation deviation can can be be seen, seen, which which is is continuously tracks localisation. Afterwards, the vehicle follows the calculated track until the destination. It stops short because of the intentionally allowed course tolerance to avoid an oscillating driving course. The track because of the intentionally allowed course tolerance to avoid an oscillating driving course. The track of the destination point to avoid excessive turning on the spot, which would cause discomfort for the correction occurring the position position (2 m|3.5 m|3.5 explained by recalibration of the the localisation correction occurring atposition the (2 m) is explained recalibration of localisation passenger. The final of the device is measured manually by (redaacross). The deviation between
system after after it it detected detected aa deviation deviation between between the the positions positions provided provided by by local local odometry odometry and and the the global global system localisation. Afterwards, the vehicle follows the calculated track until the destination. It stops short of the destination point to avoid excessive turning on the spot, which would cause discomfort for the passenger. The final position of the device is measured manually (red cross). The deviation between
World Electric Vehicle Journal 2018, 9, 48
12 of 15
localisation. Afterwards, the vehicle follows the calculated track until the destination. It stops short of the destination point to avoid excessive turning on the spot, which would cause discomfort for the World Electric Vehicle Journal 2018, 9, x FOR PEER REVIEW 12 of 15 passenger. The final position of the device is measured manually (red cross). The deviation between the 0.04 m m in in the the x-direction the calculated calculated and and the the manually manually measured measured final final position position is is − −0.04 x-direction and and 0.46 0.46 m m in in the y-direction. the y-direction.
Figure 12. 12. (a) Overview of the testing area and the test track; (b) Enlarged detail of the planned track Figure (black dotted line), planned planned waypoints waypoints (black (black crosses), crosses), start position (green cross), destination destination (orange (orange (black dotted line), cross), internally internally computed computed track (blue (blue line), line), computed computed destination destination position (blue cross), cross), manually manually measured final final position position (red (red cross). cross). measured
4. andOutlook Outlook 4. Conclusions Conclusion and In mobility device concept is In this this paper, paper,the thedevelopment developmentand andimplementation implementationofofananautonomous autonomous mobility device concept presented. The electric vehicle is designed to be part of a fleet which can be ordered on-demand by is presented. The electric vehicle is designed to be part of a fleet which can be ordered on-demand by customers distance transport transport to customers via via aa mobile mobile application application for forlast-mile/short last-mile/short distance to improve improve connectivity connectivity to to public transport systems. The system reduces the reliance on private vehicles and privately public transport systems. The system reduces the reliance on private vehicles and privately owned owned PMDs PMDs and and increases increases the the convenience convenience of of the the commuting commuting population. population. The vehicle is designed as a self-balancing, two-wheel The vehicle is designed as a self-balancing, two-wheel device device which which can can carry carry one one person person comfortably in a seated position. The size of the vehicle is determined based on anthropometric comfortably in a seated position. The size of the vehicle is determined based on anthropometric measures measures of of the the European European and and Singaporean Singaporean population. population. The The two-wheel two-wheel design design reduces reduces the the footprint footprint of the vehicle to enable travel on narrow roads and in congested areas. Driving safety and comfort are of the vehicle to enable travel on narrow roads and in congested areas. Driving safety and comfort increased by a tilt mechanism which leans the vehicle into the turn and reduces lateral forces. The tilt are increased by a tilt mechanism which leans the vehicle into the turn and reduces lateral forces. The mechanism consists of two independent linear actuators forfor a aswift tilt mechanism consists of two independent linear actuators swiftchange changeofofthe thetilt tiltof ofthe the vehicle vehicle and additionally acts as a means to lower the vehicle to the ground for easy mounting/alighting. and additionally acts as a means to lower the vehicle to the ground for easy mounting/alighting. The The effectiveness oftilt themechanism tilt mechanism ondynamic the dynamic driving behaviour is demonstrated by a effectiveness of the on the driving behaviour is demonstrated by a multimulti-body simulation and substantially increases the vehicle stability during turns. Driving comfort body simulation and substantially increases the vehicle stability during turns. Driving comfort is is increased theself-balancing self-balancingsystem systemofofthe thedevice devicebecause becauseititkeeps keeps the the passenger passenger in in an increased byby the an upright upright position, even during during travel travelover overinclined inclinedsurfaces. surfaces. Additionally, calculation of the required position, even Additionally, thethe calculation of the required tilttilt-angle based on the routing of the vehicle can potentially counter lateral forces on the passenger angle based on the routing of the vehicle can potentially counter lateral forces on the passenger more more effectively and reduced with reduced latency compared the existing tilting-devices effectively and with latency compared to thetoexisting tilting-devices whichwhich only only react react after after the occurring acceleration has been measured. In successive studies, a user study with the the occurring acceleration has been measured. In successive studies, a user study with the vehicle
should be conducted to evaluate the driving comfort, the driving speed, and the safety from a passenger’s perspective. To enable autonomous navigation, a landmark-based localisation system based on a 3D-camera system was implemented which works in conjunction with the local odometry system. The 3Dcamera system proved to be a feasible and affordable solution for navigation and localisation in situations where no localisation by GPS is possible, e.g. indoors. The accuracy is sufficient for the
World Electric Vehicle Journal 2018, 9, 48
13 of 15
vehicle should be conducted to evaluate the driving comfort, the driving speed, and the safety from a passenger’s perspective. To enable autonomous navigation, a landmark-based localisation system based on a 3D-camera system was implemented which works in conjunction with the local odometry system. The 3D-camera system proved to be a feasible and affordable solution for navigation and localisation in situations where no localisation by GPS is possible, e.g. indoors. The accuracy is sufficient for the demonstrated purposes, however the occurrence of occlusion of the landmarks can impact the localisation accuracy. For the application of higher vehicle speeds, the resolution of the camera system should be increased to enable a greater viewing range. QR-codes were used as landmarks for the presented indoor-evaluation which could be replaced by natural landmarks with an improved camera system and also to reduce the occurrence of occlusion of landmarks. The algorithms are able to detect obstacles in front of the vehicle by analysis of the camera image and the information from the ultrasound sensors to prevent collisions with any objects. This contributes to increased safety in comparison to existing PMDs without any object detection systems. The vehicle was realized as a functional prototype for demonstration and testing purposes. The selected construction with aluminium profiles and a 3D-printed shell fulfils the requirements regarding stability, the time required for the built-up, and outer appearance. The size of the vehicle footprint is similar to other PMDs with a one-axle, two-wheels setup, however it offers increased comfort because of the seated position for the passenger. The weight of the prototype is between the weight of the presented Segway and the Scewo PMD. For the realization of the prototype in mass production, a more integrated structure should be considered to reduce the overall weight of the vehicle. The selected components for the control of the system allowed for flexible integration of the conceived functionalities. The principal functionality of the autonomous operation was demonstrated, however the real-life usage is still limited by technical constraints of the self-balancing, the electrical actuators, and the accuracy of the localization system. Further development of the vehicle functions needs to be carried out to increase the operating speed and the overall stability of the autonomous navigation functions. Going forward, the presented concept shows a possible solution for the first/last mile problem and can contribute to improving the ridership of public transport to reduce the reliance on private vehicles for transport in megacities. Besides closing the gap for the first/last mile, the small footprint of the vehicle enables the vehicle to operate in other public areas, including airports and shopping malls, where longer walking distances could be reduced. Author Contributions: Conceptualization, M.K., F.R., M.W., B.H., T.H., L.L.S., J.S.D.L., Y.L., V.M., M.L., W.X.R.T., and M.L.; Investigation, B.H., T.H., V.M., and M.L.; Methodology, B.H., T.H., L.L.S., J.S.D.L., Y.L., V.M., M.L., and W.X.R.T.; Project administration, M.K., F.R., and M.W.; Resources, M.K., F.R., Michael Wittmann, Y.J.J.H., and H.W.N.; Supervision, M.K., F.R., M.W., Y.J.J.H., and H.W.N.; Visualization, L.L.S. and J.S.D.L.; Writing—original draft, M.K., B.H., T.H., V.M., and M.L.; Writing—review and editing, F.R., M.W., A.O., and M.L. Funding: This work was financially supported by the Singapore National Research Foundation under its Campus for Research Excellence and Technological Enterprise (CREATE) programme and by the German Research Foundation (DFG) and the Technical University of Munich (TUM) in the framework of the Open Access Publishing Program. Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of the data; in the writing of the manuscript, or in the decision to publish the results.
References 1. 2. 3.
United Nations. World Urbanization Prospects. The 2014 Revision: Highlights; UN: New York, NY, USA, 2014; ISBN 978-92-1-151517-6. Polzin, S. Setting Expectations for Mobility as a Service. Available online: https://www.planetizen.com/ node/90839 (accessed on 20 March 2018). Brooks, R.A. Seat for Self-Propelled Narrow-Track Vehicle. U.S. Patent No 5,857,535, 12 January 1999.
World Electric Vehicle Journal 2018, 9, 48
4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
14.
15. 16. 17. 18.
19.
20. 21. 22.
23. 24. 25. 26. 27.
14 of 15
Saeger, M.; Simon, M.; Valluri, A. Method for Operating a Tilting Running Gear and an Active Tilting Running Gear for a Non-Rail-Bourne Vehicle. U.S. Patent No 9,821,620, 21 November 2017. Ishii, S.; Yamano, I. Travel Device. U.S. Patent Application No 11/984,154, 19 June 2008. Yuji Hosoda, S.; Egawa, J.; Tamamoto; Nakmura, R.; Horiuchi, T. Mobile Robot. U.S. Patent 7,649,331 B2, 19 January 2010. Segway Inc. Our Story. Available online: http://www.segway.com/about/our-story (accessed on 23 October 2017). Segway Inc. Reference Manual. Segway Personal Transporter (PT) i2, x2. Available online: http://www. segway.com/media/1688/referencemanual.pdf (accessed on 23 October 2017). Scewo. Scewo Bro Brochure. Available online: https://scewo.ch/wp-content/uploads/2018/10/ScewoBro_A5_EN.pdf (accessed on 20 November 2018). Airwheel Unicycles. Airwheel X8. Available online: http://airwheelunicycle.com/Airwheel-X8 (accessed on 23 May 2018). Zoom Urban Transport. Zoom Stryder Electric Scooter. Available online: https://www.ridezoom.co/ (accessed on 23 September 2018). Scewo. Scewo Press Kit. Available online: https://scewo.ch/ (accessed on 20 November 2018). Andersen, H.; Eng, Y.H.; Leong, W.K.; Zhang, C.; Kong, H.X.; Pendleton, S.; Ang, M.H.; Rus, D. Autonomous personal mobility scooter for multi-class mobility-on-demand service. In Proceedings of the 2016 IEEE 19th International Conference on Intelligent Transportation Systems (ITSC), Rio de Janeiro, Brazil, 1–4 November 2016; pp. 1753–1760. Kleine ergonomische Datensammlung; Lange, W.; Windel, A.; Kirchner, J.-H.; Bundesanstalt für Arbeitsschutz und Arbeitsmedizin (Eds.) Praxiswissen Arbeitssicherheit; 13., aktualisierte Aufl.; TÜV-Media: Köln, Germany, 2009; ISBN 978-3-8249-1244-5. Chuan, T.K.; Hartono, M.; Kumar, N. Anthropometry of the Singaporean and Indonesian populations. Int. J. Ind. Ergonom. 2010, 40, 757–766. [CrossRef] Hatam, B.; Herrmann, T.; Medovy, V.; Merkle, L.; Lim, J.S.D.; Sim, L.L.; Lu, Y.; Ten, W.X.R. Team “Micromobility” Final Report globalDrive 16/17. 2017; Unpublished Results. DIN 18040-1:2010-10: Barrierefreies Bauen—Planungsgrundlagen—Teil 1: Öffentlich zugängliche Gebäude. 2010. Available online: https://nullbarriere.de/din18040-1.htm (accessed on 24 October 2017). Building and Construction Authority Singapore. Code on Accessibility in the Built Environment 2013. Available online: https://www.bca.gov.sg/BarrierFree/others/ACCESSIBILITY_CODE_2013.pdf (accessed on 24 October 2017). Thomson Industries. Pro-Series/Electromechanical Linear Actuator—Installation and Operation Manual. Available online: https://www.thomsonlinear.com/downloads/actuators/Electrak_Pro_Series_mnen.pdf (accessed on 24 October 2017). AAEON Technology (Europe), B.V. Up Board—Specification. Available online: http://www.up-board.org/ wp-content/uploads/2016/05/UPDatasheetV8.5.pdf (accessed on 6 October 2017). Libmraa—Low Level Skeleton Library for Communication on GNU/Linux platforms. Available online: https://github.com/intel-iot-devkit/mraa (accessed on 2 June 2018). Intel Corporation. Intel RealSense Camera R200: Embedded Infrared Assisted Stereovision 3D Imaging System with Color Camera: Product Datasheet. Available online: https://www.mouser.com/pdfdocs/intel_ realsense_camera_r200.pdf (accessed on 15 January 2018). Arduino, s.r.l. Arduino Due—Tech Specs. Available online: https://store.arduino.cc/usa/arduino-due (accessed on 15 January 2018). Arduino, s.r.l. Arduino Leonardo—Tech Specs. Available online: https://store.arduino.cc/usa/arduinoleonardo-with-headers (accessed on 15 January 2018). ROS ROS History. Available online: http://www.ros.org/history/ (accessed on 25 October 2017). dmg-movement. Motoren Übersicht. Available online: http://www.dmg-movement.de/Motoren.htm (accessed on 15 January 2018). Roboteq. Brushless DC Motor Controllers: FBL2360. Available online: https://www.roboteq.com/index. php/roboteq-products-and-services/brushless-dc-motor-controllers/324/fbl2360-detail (accessed on 15 January 2018).
World Electric Vehicle Journal 2018, 9, 48
28.
29. 30. 31. 32. 33.
15 of 15
Linergy Engineering GmbH. Fahrradakku LiFePO4 6V/2,5Ah-25Ah aus A123 ANR26650 Zellen—A Version. Available online: https://www.linergy-shop.de/de/Fahrradakku-LiFePO4-36V-2-3Ah-aus-A123ANR26650-Zellen---A-Version---315-425-1065.html (accessed on 15 January 2018). Arduino, s.r.l. Arduino 101—Tech Specs. Available online: https://store.arduino.cc/usa/arduino-101 (accessed on 15 January 2018). Ultrasonic Ranging Module HC—SR04. Available online: https://cdn.sparkfun.com/datasheets/Sensors/ Proximity/HCSR04.pdf (accessed on 15 January 2018). Borenstein, J.; Everett, H.R.; Feng, L. Where am I? Sensors and Methods for Mobile Robot Positioning; University of Michigan: Ann Arbor, MI, USA, 2016. Computer Vision; Ikeuchi, K. (Ed.) Springer US: Boston, MA, USA, 2014; ISBN 978-0-387-30771-8. MayTec Aluminium Systemtechnik GmbH the MayTec Connection System. Available online: http://www. maytec.de (accessed on 15 January 2018). © 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
