Measuring astronaut performance on the ISS ... - Semantic Scholar

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IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 50, NO. 5, OCTOBER 2001

Measuring Astronaut Performance on the ISS: Advanced Kinematic and Kinetic Instrumentation Amir R. Amir, Guido Baroni, Alessandra Pedrocchi, Dava J. Newman, Giancarlo Ferrigno, and Antonio Pedotti

Abstract—This paper presents the design of an advanced kinematic and kinetic measurement system for the International Space Station (ISS). Massachusetts Institute of Technology (MIT), NASA, Politecnico di Milano University, and the Italian Space Agency are currently developing jointly an integrated system capable of precisely measuring the forces and moments the astronauts induce and their postures and movements. Kinetic measurements will be performed with special crew restraint and mobility aids instrumented with strain gages. The compact electronics component of the sensors provides real-time feedback of the load level applied. The kinematic measurements of astronaut motion will be accomplished with ELITE-S2, a general purpose opto-electronic motion analysis system proposed for the ISS by the Italian Space Agency (Agenzia Spaziale Italiana, ASI) with the support of the French Space Agency (Centre National d’Etudes Spatiales, CNES). This versatile motion capture system provides three–dimensional (3-D) kinematics data in real-time using video-image processing for detecting multiple passive markers. Index Terms—Biomechanics, force measurement, motion analysis, motion measurement, space stations, space technology, torque measurement.

I. INTRODUCTION

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UANTITATIVE analysis of human performance in microgravity is important for both scientific investigations and spacecraft engineering design. By collecting and evaluating the kinematic and kinetic data of astronauts in space, it becomes possible to characterize human motor strategies, postural behavior in weightlessness [1], [2], improve the design of orbital modules, help maintain a quiescent microgravity environment for acceleration-sensitive science experiments [3], and optimize the human operative capabilities during long-duration space missions [4]. Consequently, there is a need for a precise measurement of the forces and moments exerted by the astronauts on the space station and quantification of their postures and movements. An integrated system of advanced kinematic and kinetic instruments to make these measurements on the International Space Station (ISS) is being developed jointly by the Massachusetts Institute of Technology (MIT), NASA, Politecnico di Milano University, and the Italian Space Agency (Agenzia Spaziale Italiana, ASI) in a project known as Microgravity Manuscript received May 26, 1999; revised April 25, 2001. The ELITE-S2 project was supported by ASI. The MICRO-G effort was supported by NASA through Research Grant NAG 9-1003. A. R. Amir and D. J. Newman are with the Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139 USA (e-mail: [email protected]). G. Baroni, A. Pedrocchi, G. Ferrigno, and A. Pedotti are with the Department of Bioengineering, Politecnico di Milano University, Milan, Italy. Publisher Item Identifier S 0018-9456(01)09720-0.

Investigation and Crew Reactions in 0-Gravity (MICR0-G). Astronaut-induced forces and moments will be measured by an advanced version of the dynamic load sensors that have flown on the space shuttle during Mission STS-62 in March of 1994 [5] and on the Russian orbital complex Mir from May 1996 to May 1997. Crew motions will be captured by the ELITE-S2 system, an enhanced version of the real-time opto-electronic motion analyzers ELITE-S and Kinelite, flown respectively on Mir as part of the EuroMir 1995 Mission [6] and on Neurolab [7]. ELITE-S2 is the human motion analysis system proposed to the European Space Agency (ESA) for the Experimental Physiology Module by ASI in collaboration with the Department of Bioengineering at Politecnico di Milano University with the contribution of the French Space Agency (Centre National d’Etudes Spatiales, CNES) [8]. II. ADVANCED KINETIC SENSORS The advanced kinetic sensors are an instrumented version [9] of the crew restraint and mobility devices to be provided on the International Space Station (ISS) [10]. In particular, the functionalities of a hand hold, a foot restraint, and a push-off pad are offered while measuring the forces and moments in three axes (six degrees of freedom) applied to the sensor. The kinetic sensors of the MICR0-G system are based on the dynamic load sensors that have flown aboard the Space Shuttle and Mir. New requirements for the re-design of the sensor system were stated as follows: • acquisition and processing of data in real-time and immediate feedback to the astronaut; • miniaturization of electronics to maximize mobility and flexibility of the load sensors; • simplification of the operation for astronauts; • possibility of on-orbit maintenance and repairs; • communication and synchronization with ELITE-S2; • compatibility with the ISS (power, restraint aids, common data bus, etc.); • Maximum use of commercial off-the-shelf (COTS) technologies to reduce development and production costs. Each advanced load sensor consists of two parts: the sensor restraint unit (SRU) and the sensor electronics unit (SEU) as shown in Fig. 1. The former contains, as the name implies, the astronaut restraint mechanism (either a handle or a foot loop), as well as the load cells to measure forces and moments. The latter contains all the necessary electronics for data processing, storage, data display, etc. The SRU is attached to standard ISS hand rails or so-called seat track anchor interfaces [10].

0018–9456/01$10.00 © 2001 IEEE

AMIR et al.: MEASURING ASTRONAUT PERFORMANCE ON THE ISS: ADVANCED KINEMATIC AND KINETIC INSTRUMENTATION

Fig. 1.

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Configuration of an advanced kinetic sensor.

A. Sensor Restraint Unit (SRU) Each sensor measures about 24 24 2 centimeters and is manufactured from AL 7075-T63 aluminum. The measurement of forces and moments is accomplished with three custom-designed load cells (so-called flexures) in a circular arrangement placed 120 apart as shown in Fig. 2. Each load cell is equipped with two full Wheatstone strain gage bridges consisting of four foil strain gages. Two strain gages are on top of a center beam and two are on the bottom. Similarly, two strain gages are on the outside of a side beam and two are on the inside. Full bridges are used to nearly double the measurement sensitivity and to compensate for temperature effects. Three signals are from bridges on the center beams and three signals are from bridges on the side beams of the load cells. The sensor feeds the data acquisition computer with six signals that measure the deflection of the load cells. The sensor enclosure and the flexures were designed for a full scale load of 400 N of force and 50 N m of torque. The experience of the Shuttle-Mir program has shown that it is important to calibrate sensors as often as possible since the effects of long-duration spaceflight on the equipment remain difficult to predict. To convert the signal measured by the SRU into an applied load, a so-called calibration matrix is required. Given a 6-element vector consisting of the applied -, -, and -force components and the three applied -, -, and -moment comof the corresponding measurements of ponents and a vector the deflections of the load cells, the relationship between the two quantities is

where is the calibration matrix reflecting various properties of a sensor’s specific enclosure, load cells, strain gages, etc. The matrix is determined not through a single measurement but

through a series of calibration measurements in which various known weights and moments are applied to the sensor. Then the matrix consists of three applied forces and three applied moments arranged in columns and the columns contain different applied weight and moment configurations. The elements of the matrix have units of either Newtons or Newton-meters. matrix consists of the corresponding measureThe ments—in units of Volts. The matrix is then computed by the as follows: method of least squares from and

Following the 24-month stay on Mir, the sensors were examined and recalibrated. Overall, the devices were in a very good condition—only the screws were slightly corroded. The postflight calibration of the spaceflight sensors showed that the accuracy was within 1.6% of the full scale load for all four sensors that were sent to the orbital complex [9]. Due to this excellent result, only one modification is being implemented. The restraint mechanism will be reconfigurable in orbit without any tools, so that the astronauts can change the foot restraint into a hand hold and vice versa or remove it to obtain an instrumented push-off pad. B. Sensor Electronics Unit (SEU) Each sensor is connected via a cable to a corresponding SEU, 24 10 centimeters. The electronics in the measuring 24 SEU is based on the PowerPAQ handheld reference design. Developed by Motorola’s Inc. Semiconductor Division, the PowerPAQ is a reference platform for embedded systems with applications such as image capture, wireless connectivity, speech recognition, and Global Positioning System receivers [11]. The design objective for the PowerPAQ was to demonstrate how much performance and functionality can be packed into a small

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Fig. 2. Arrangement of load cells in the SRU.

embedded system. For the kinetics sensors, much fewer components and I/O ports will be used than are contained in a standard PowerPAQ, whose interior is shown in Fig. 3. The SEU consists internally of three layers. At the bottom of the unit is a six-channel signal conditioning card, which is connected to the SRU. It supplies the excitation voltage to the three load cells and conditions the voltage signal returned from the load cells. The second layer of the SEU consists of the processing and data storage components. The signal is sampled with a commercial PC Card Type II 16-bit A/D converter housed in one of the two PC-Card readers. Typically, data will be recorded with a 250 Hz sampling frequency and sent through a third order low-pass filter. The central processor of the SEU is Motorola’s 32-bit MPC823, which belongs to the MPC8xx family of embedded PowerPC™ processors. Running at 50 MHz, it achieves 66 MIPS [12]. Raw data processed with the calibration matrix is stored on spaceflight-qualified Type III PC-Cards from Calluna Technology Ltd. These miniature hard disks provide a capacity of up to 1.04 gigabytes. Time synchronization with the space station is accomplished with a Datum Inc. (Bancomm Division) time card using the IRIG timer signal. A universal serial bus (USB) port is included for communication between load sensors and the ELITE-S2 system. The SEU’s third layer is made up of the color TFT display (16.3 cm diagonally) with a touch screen for input supplemented with an internal microphone to digitally record crew comments. The Windows CE™ operating system with a custom

Fig. 3. Inside view of a PowerPAQ reference design as provided by the manufacturer.

application, designed for ease-of-use, is employed for operating the sensors with the capability to provide a visual and auditory warning if the sensors measure a load exceeding a specified level. The touch screen is large enough to permit the use of a finger instead of a stylus for interfacing with the application. The specifications of the SEU are summarized in Table I. It incorporates most of the features of the previous device and overall greatly improves the performance. With a volume of only 5800 cm , the SEU will be about eight times smaller than


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TABLE I MAJOR SPECIFICATIONS OF THE SEU

Fig. 4.

Architecture of the ELITE-S2 motion analysis system.

the data acquisition computer flown on Mir. Since it has fewer data acquisition and supports only a single sensor, the relative reduction in size is about a factor of three. For extra flexibility, each SEU will accept any SRU. III. ELITE-S2 The kinematic measurement component of the MICR0-G system will consist of a versatile opto-electronic motion analyzer designed to fulfill a variety of different experimental requirements and protocols. The system allows varying the field of view, duration of the acquisition, number of markers, number of active video cameras, and the system sampling rate. In particular, the on-going feasibility study of ELITE-S2, performed by the Department of Bioengineering of Politecnico di Milano for ASI, aims to improve the currently available spacequalified technology for automatic motion analysis in order to • work at a frequency of 250 Hz • reduce by one-half the size of the markers • double the accuracy of the marker localization, even in comparison with the most recent space-qualified version of the ELITE system (Kinelite system) [7]. The system will be equipped with custom-made CCD TV cameras (TVCs) with a resolution of 512 512 pixels. A special feature will be the real-time 3-D reconstruction of the marker coordinates, thus opening the possibility of many new applications, such as virtual training [13]. The modular architecture of ELITE-S2 is shown in Fig. 4. The system is composed of four to 16 TVC units, each containing a video camera and dedicated electronics performing the first round of image processing. The TVC units are connected through a bus with an IBM Thinkpad 760/770 laptop. A very important innovation of ELITE-S2 over the previous ELITE systems is a much faster and swifter operation. Only one astronaut will be needed to perform the calibration procedure, the operational set-up of the acquisition, and serve as the subject of the acquisition, thus reducing by almost one-half the crew time necessary for each experimental session. A. TVC Units Each TVC unit includes the following components, as shown in Fig. 5 • power distribution; • video camera (optics); • illumination system;

Fig. 5. Block diagram of the components making up a TVC unit.

• microprocessor for the control of the experimental setup and image resolution enhancement; • image processor with the dedicated hardware for marker recognition. At the present stage, a possibility is to use the DALSA CA-D6 video camera, which still needs to be qualified for operation aboard the ISS. In this case, the sensors store the digital image data in four CCD readout shift registers and process 532 516 pixels at 262 Hz. Alternatively, a custom-made video camera will be built on the EGPG RETICON CCD sensor, providing a 512 512 image resolution. In both cases, the four camera registers are read by the image processor, which performs the computation to recognize the shape of the markers. The recognition algorithm is inherited from the ground motion analyzer ELITE [6], [14] and is based on a two-dimensional cross-correlation between the image and an appropriate kernel representing the shape of the marker. The image processor first formats the image by arranging the data as necessary for the subsequent correlation procedure. Two-dimensional coordinates and the computed value of the cross-correlation function of all those pixels recognized as belonging to a marker are sent to the microprocessor. Fed with software by the laptop computer, the microprocessor performs various operations; it • controls and regulates the optics; • defines the integration time and the vertical synchronization for the camera; • receives from the image processor the coordinates of all pixels recognized as part of a marker along with the correspondent value of the cross-correlation function; • performs the resolution enhancement procedure, consisting of the calculation of the centroid of each marker as

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the weighted average (where the cross-correlation value is the “weight” in the averaging procedure) of all the pixels belonging to a specific marker; • corrects marker coordinates for optical distortions; • communicates with the data logger (laptop computer), sending the enhanced marker two-dimensional coordinates; • generates the signal for frame synchronization among all the active video cameras as well as analog synchronization for the interfacing with systems for synergistic analog data collection. The optics will be equipped with three different illumination sources in the near infrared region (750–900 nm). The illumination sources will be selectable on each TVC unit separately, in order to differentiate the illumination characteristics between the active TVC units. In combination with interferometer filters, corresponding to the three different laser wavelengths, and applied to the TVC optics, it will be possible to eliminate the disturbing effects generated by the illumination devices of different active TVC units when one is in front of the other. Each TVC unit will be equipped with two fixed optics in order to define two different fields of view—one for whole body acquisition with a maximum dimension of 3 m and the other for upper body acquisition with a maximum dimension of 2 m. The presetting of optics characteristics will allow a preliminary calibration of the TVC internal parameters. This feature will greatly reduce the time necessary for the calibration procedure.

The introduction of a set of optics with relative pre-calibration parameters will allow using a very quick calibration procedure based on the use of a bar or a triangle (a plastic bar of known length with two markers on the extremities), which has to be moved in the working field of view by the operator at the beginning of the experimental session [15]. The calibration procedure will be completed by the simple acquisition of three nonaligned markers providing the absolute frame of reference. In addition, the possibility of a complete calibration of the system, including the unstated parameters, will be made available for redundancy [15]. Another important innovation is based on the availability of different illumination sources on each TVC unit, which allows the development of wavelength-selective passive markers. The traditional ELITE/ELITE-S markers (hemispheric plastic supports covered by retroreflective 3M Scotchlite material) will be encapsulated in hemispherical glass filters with different high-pass characteristics. Consequently in experimental protocols where a superposition of markers is possible, the two or three markers most critical will be covered with different filters. With the alternation of the illumination sources, the system will be able to distinguish which markers are visible at each frame, improving the tracking procedure and reducing reconstruction errors. This solution will be particularly important for experimental protocols where real-time 3-D reconstruction will be necessary.

IV. SUMMARY B. System Bus The system bus connects the laptop to the TVC units and is used for uploading the software from the laptop computer controlling the acquisition. Camera control commands, power supply and data transmission will run on the serial bus, with a peak data rate of 3.2 Mbit/s. The network connection among TVC units and the laptop computer will be implemented with an ARCNET token passing protocol. Each TVC unit will be equipped with a COM20022 ARCNET interface micro controller, while a PC Card PCM20-5 will be used for the laptop to interface with the network. C. Laptop Computer The laptop computer (IBM ThinkPad 760/770) will control the processors installed in each TVC unit and used by the operator to oversee the data acquisition. In addition, it will be responsible for the synchronization with any additional hardware. Accordingly, the laptop will be equipped with a DAQ 770 PCMCIA, providing a synchronization digital output. However, the most likely interface for synchronizing/communicating with the advanced load sensors will be a dedicated USB connection. D. Additional Equipment for Procedural Issues Two more improvements over previous versions are worthy to be mentioned: the innovation of the calibration procedure, which is a key point for a faster operation, and the development of wavelength selective markers, which will greatly simplify the reconstruction procedure.

The MICRO-G research effort is a successful international collaboration that leverages two previously proven spaceflight instruments and improves as well as integrates them into a comprehensive package for quantifying astronaut loads, posture and movement in weightlessness. This efficient working relationship offers the space agencies involved an order of magnitude reduction in flight hardware costs. Following a brief description of the importance of making human performance measurements on the International Space Station and the heritage of the advanced kinematic and kinetic instrumentation, the current design was presented. The measurement of crew-induced forces and moments will be accomplished with an advanced version of the dynamic load sensors previously flown on the Space Shuttle and on Mir. Using more sophisticated electronics, real-time feedback of the applied load as well as a reduction in size by a factor of eight in comparison to the previous device will become possible. Using a 16.3 cm color flat panel display with a touch screen, the operation of the system will be greatly simplified. A universal serial bus connection will be used to synchronize the internal time and share other pertinent data among several load sensors and the ELITE-S2 system. The latter is proposed for use on the ISS as a general purpose motion analysis system achieving a significant performance improvement over the previous spaceflight-qualified system. It will double the accuracy of marker localization and record data at a frequency of 250 Hz to work concurrently with the load sensors. Further, a real-time 3-D determination of marker coordinates will permit many new applications. The ELITE-S2 will also strongly improve the speed of operation


through a quicker calibration procedure and operational set-up, allowing one astronaut to be operator and subject at the same time. REFERENCES [1] J. Massion, “Movement, posture, and equilibrium: Interaction and co-ordination,” Progr. Neurobiol., vol. 38, pp. 35–36, 1992. [2] M. Tryfonidis, D. J. Newman, and C.-S. Poon, “Bayesian optimization of visuomotor performance revealed in microgravity,” Science, June 1999. [3] NASA Johnson Space Center, “Microgravity Control Plan,” SSP 50036, Revision A, Type 2, NASA, Feb. 29, 1996. [4] H. A. Wichman and S. I. Donaldson, “Remote ergonomics research in space: Spacelab findings and a proposal,” Aviation Space Environ. Med., vol. 67, no. 2, pp. 171–175, 1996. [5] D. J. Newman, M. Tryfonidis, and M. C. van Schoor, “Astronaut-induced disturbances in microgravity,” J. Spacecraft Rockets, vol. 34, no. 2, Mar.–Apr. 1997. [6] G. Ferrigno and A. Pedotti, “ELITE: A digital dedicated hardware system for movement analysis via real-time TV-signal processing,” IEEE Trans. Biomed. Eng., vol. BME–32, pp. 943–950, 1985. [7] M. Venet, H. Picard, J. McIntyre, A. Berthoz, and F. Lacquaniti, “The Kinelite project: A new powerful motion analizer for SpaceLab and Space Station,” Acta Astronautica, vol. 43, no. 6, pp. 277–289, 1998. [8] A. Pedrocchi, G. Baroni, A. Pedotti, and G. Ferrigno, “ELITE-S2, the human motion analysis facility for the ISS: Technological characterization and potential application for multifactorial movement analysis in microgravity,” in Proc. II ESA Symp. ISS Utilization. Noordweijk, The Netherlands, Nov. 1998. [9] A. R. Amir, “Design and development of advanced load sensors for the International Space Station,” Engineer in aeronautics and astronautics thesis, Mass. Inst. Technol., Cambridge, 1998. [10] M. P. Centanni and D. Pogue, Flight Crew Support and Integration (FCS&I): The Boeing Company, Seattle, WA, 1997. [11] Motorola Consumer Systems Group, “Product information: PowerPAQ handheld reference design,” 1998. [12] Motorola Semiconductor Division, “PowerPC 823 User’s Manual,” MPC823UM/D. [13] G. Baroni, G. Ferrigno, and A. Pedotti, “Implementation and application of real-time motion analysis based on passive markers,” Med. Biol. Eng. Comput., vol. 36, no. 6, pp. 693–703, 1998. [14] G. Ferrigno and A. Pedotti, “Modularly expansible system for real-time processing of a TV display, useful in particular for the acquisition of coordinates of known shapes objects,” U.S. Patent 4 706 296, Patent and Trademark Office, Washington, DC, 1990. [15] P. Cerveri, N. A. Borghese, and A. Pedotti, “Complete calibration of a stereo photogrammetric system through control points of unknown coordinates,” J. Biomech., vol. 31, no. 10, pp. 935–940.

Amir R. Amir received the S.B. (1993), S.M. (1995), and Engineers degrees (1998) from the Department of Aeronautics and Astronautics of the Massachusetts Institute of Technology (MIT), Cambridge. He is currently working as a Consultant for McKinsey and Company, Miami, FL. His interests include aerospace bioengineering, systems engineering, and space propulsion.

Guido Baroni received the Ph.D. degree in bioengineering in 1998 from the Politecnico di Milano University, Milan, Italy, where he is currently an Assistant Professor. His interests cover motion analysis technologies applied to the study of human motor control and postural regulation, related to the neurophysiology of movement and biomechanics.

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Alessandra Pedrocchi received the Laurea degree in electrical engineering in 1997 and the Ph.D. degree in bioengineering in 2001 from the Politecnico di Milano University, Milan, Italy. She is now Research Assistant at the Department of Bioengineering, Politecnico di Milano. Her main interests are in motor control with special attention to extreme environments, biomechanics, motion analyzers technology, and MEMS application in bioengineering.

Dava J. Newman was born in Helena, MT. She received the B.S. degree in aerospace engineering from the University of Notre Dame, Notre Dame, IN, in 1986, the S.M. degree in aeronautics and astronautics and the S.M. degree in technology and policy in 1989, and the Ph.D. degree in aerospace biomedical engineering in 1992 from the Massachusetts Institute of Technology (MIT), Cambridge, MA. She is currently an Associate Professor of aeronautics and astronautics at MIT. Her interests include aerospace bioengineering, control and dynamics, biomechanics, human factors engineering, and systems engineering. She has been the Principal Investigator on three space flight experiments to study astronaut performance on the Space Shuttle and Russian MIR Space Station. Dr. Newman is a member the American Association of University Women (AAUW), the American Institute of Aeronautics and Astronauts (AIAA), the Aerospace Human Factors Association (AsHFA), Aerospace Medical Association (AsMA), the American Society for Engineering Education (ASEE), the American Society of Biomechanics, the International Society of Biomechanics (ISB), the OmniSport 2001 (nonprofit org. supporting education for athletes), Sigma Xi—The Scientific Research Society, the Society of Women Engineers (SWE), the Space Studies Institute (SSI), and the Union of Concerned Scientists (UCS) for Peace. She currently serves on the National Academy’s Aeronautics and Space Engineering Board and is an AIAA Distinguished Lecturer.

Giancarlo Ferrigno was born in Pozzuoli, Italy. He received the Laurea degree in electronics engineering in 1983 and the Ph.D. degree in bioengineering in 1990 from the Politecnico di Milano, Milan, Italy, where he is currently an Associate Professor of electronic and information Bbioengineering. His interests include motor control bioengineering, instrumentation and signal processing for motion analysis, and biomedical instrumentation in general. He has been involved in the development of Elite-s system and its scientific utilization on the MIR space station. He was responsible for a program at the Politecnico di Milano in phase A and phase B studies of Elite-S2 and is currently involved in a program for phase C/D.

Antonio Pedotti received a degree in electronic engineering in 1968 from the Politecnico di Milano, Milan, Italy. He is Full Professor of bioengineering and biomedical technology at the Politecnico di Milano. He is Founder and Director of the Bioengineering Center, Milan, Italy, jointly sponsored by the Pro Juventute Foundation and the Politecnico di Milano. During his career, he has performed research in bioengineering with particular reference to the analysis of neuromotor control with application in motor disorders, prostheses, rehabilitation, ergonomics, and sport. In this field, he has given a great contribution to the development of new technologies and systems of movement analysis based on pattern recognition and computer vision procedures, 3-D imaging and multimedia technologies are also subject of his research work. Other fields of interest recover natural and artificial sensors, neural networks, biotechnology and simulation of biological system, image processing, and robotics.