A Collaborative Method Between CAD and CAR Software for Robotic ...

2nd International Conference on Information Technology and Electronic Commerce （ICITEC 2014）

A Collaborative Method Between CAD and CAR Software for Robotic Cells Design Xinyu Fang, Jiafan Zhang, Member, IEEE ABB Corporate Research Center Shanghai 201319, China [email protected], [email protected] 1) The robotic cell/line layout is designed in CAD environment while checking the robot reachability, collision and cycle time performance should be implemented in CAR;

Abstract—This paper presents a collaborative method to make full use of the advantages of CAD and CAR (Computer aided robot) software in industrial robotic application. CAR software is a necessary tool in robotic cell design with robot programming and robotic cell/line performance simulation with imported CAD model. However, due to the lack of efficient channel between CAD and CAR, the check-and-change design loop is always time consuming. This paper illustrates how to link these two types of software with an intermediate file, which records geometric data of CAD model and robot simulation information as well. With the implementation of this method, a high efficient design-simulation loop is set up and the productivity is highly improved on the engineering site. Finally this paper gives a concrete demonstration. Keywords—Collaborative application

I.

method,

CAD,

CAR,

2) The robotic cell/line is usually designed in parallel with the new proposed product and the design changing always happens during the robotic cell/line proposal phase. Fig.1 illustrates this check-and-change loop.

Robotic

INTRODUCTION

With the increasing demand for high productivity, high quality, and more flexibility, more and more robots are involved into current industrial fields. To help engineers to design and implement such robotic application, normally two types of software are employed, say CAD (Computer Aided Design) and CAR (Computer Aided Robot).

Fig. 1. Traditional procedure to combine CAD and CAR software

Although CAR, generally, provides an interface to import CAD model into itself, yet, the only information can be exchanged between CAD and CAR is the geometrical information, and furthermore it is one direction, namely from CAD to CAR. Obviously, it is far away from satisfaction. Some advanced CAR software supports to teach the robot target points by capturing the geometrical features, yet this capture function is not as powerful as that in the CAD software. For example, one auxiliary line is introduced to help generate a robot path based on a certain geometrical feature, as shown in Fig.2. However there is a gap between this auxiliary line and the geometry in any CAR software. Once the design is changed, the CAD model should be imported again, and the existing auxiliary could not be synchronized automatically. The engineer should re-add one and re-generate the robot path. In the robotic cell proposal phase, the frequent design changing always makes this repeated work no-value added.

A typical scenario to implement a robotic application can be summarized as the following steps: 1) Mechanical design of the application environment including fixture, cell layout or line layout, etc. in CAD; 2) Importing the pre-designed models from CAD to CAR and generating robot targets and paths in CAR for simulation; 3)

Robotic application simulation and verification;

4) Manufacturing and assembly according to the CAD models; 5) On-site tuning, pre-serial production and up to mass production. The first three steps in above mentioned design flow can be regarded as the design phase of a robotic cell/line. It is usually not straight forward attributed to two main reasons:

978-1-4799-5299-1/14/$31.00 ©2014 IEEE

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Dalian, China

In this paper, a collaborative method to interconnect the CAD and CAR software is formally outlined. The implementation of the proposed solution is introduced in Section 3, followed by conclusions. II. METHODOLOGY CAD and CAR are two popular used engineering software in mechanical design and robot simulation. Both of them have powerful features in specific areas. If a seamless interface could be set up to bridge them, it could efficiently reduce the number of check-and-change loop, and shorten the proposal leading time to customers.

Fig. 2. Auxiliary line to help generating robot path based on a certain geometrical feature in CAR software

On the other hand, if the robotic cell/line performance simulation is failed, for example, the working area is out of robot reachability, the mechanical design should be revised in the CAD environment, in accordance with the message from robot simulation engineers. However, communication misunderstanding or message transmission errors usually happen.

Fig. 1 gives a typical case in robot application design today. Actually, CAD software has powerful function to synchronize reference object change when the CAD model is modified. For example, the similar case is shown in Fig.3. If the original cuboid is stretched in CAD software, the auxiliary line attached with the cuboid will be extended automatically. And the robot path line attached with the auxiliary line will be updated as well. This function is the key point for the collaborative method to combine CAD and CAR software for robotic cell design.

In order to bridge the gap in this area, several progresses were achieved in the past years. One popular solution is to establish the CAD-based robot programming method. This method is to extract the information from the CAD and convert it into robot commands in CAD software directly. It is convenient for some medium or small enterprises, where the skilled robot programming work is lack, although this method fully takes advantages of CAD software when design changing occurs. The work in [1] presents a CAD-based system to program a robot from a 3D CAD environment and a human-robot interface is developed. A simulation system with a relative low cost and an available 3D CAD package to visualize preprogrammed robot paths is presented in [2]. Li introduces a preliminary research work about synchronized collaborative design based on heterogeneous CAD systems and a prototype of synchronized collaborative design is developed based on MDT and Solidworks with their APIs and VC++ [3]. A similar work with distributed collaborative design framework and a prototype system of collaboratively heterogeneous CAD system is introduced in [4]. Reference [5] presents a design of pick and place robotics system with Solidworks Softmotion software. Practically, a specific study on pickplace application is implemented based on Solidworks Softmotion software. However, above solutions miss the advantages from in CARs, most of which are published by robot manufacturers, with more accurate cycle time, motion control simulation.

Fig. 3. Auxiliary line to help generating robot path based on a certain geometrical feature in CAD software

As a result, some geometrical objects, including point, frame and axis, can be introduced in the CAD model as the references. The proposed method makes fully use of these reference geometrical information. During mechanical design phase, some important robot targets and paths can be defined by means of corresponding reference geometrical objects, as summarized in Table 1.

Another well-known concept proposed recently is AutomationML (Automation Markup Language), which is a XML (eXtensible Markup Language) based data format to store and exchange engineering information. Its basic architecture is developed by companies and the universities [8]. AutomationML gives the possibility to interconnect the various engineering tools in their different disciplines [67][11]. This concept defines an open standard to integrate the heterogeneous engineering tools, including tools used in robotic application, like the example given in [10]. Reference [9] gives encouraging results of a research and development activity of the AutomationML society to reduce the AutomationML programming effort.

TABLE I.

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INFORMATION MAPPING BETWEEN CAD AND CAR SOFTWARE

Geometrical information in CAD software

Robot simulation object in CAR software

Reference coordinate system

Robot target


Work object


Tool center point

Line

Robot Path

Arc

Robot Path

For example, a target point of robot TCP (tool center position) is defined with position and orientation. Therefore a reference point with a reference coordinate system can be used to represent a robot target point in the CAD model, as shown in Fig.4.

Fig. 5. Efficient methods to share geometric information between CAD and CAR software

III.

IMPLEMENTATION

According to the guideline of the above methodology, two add-ins are designed and developed respectively for CAD and CAR software. In this work, SolidWorks and RobotStudio are selected as CAD and CAR platform for verification. To implement the two add-ins, the programming language is based on C# with VisualStudio 2012. In the following sections, the implementation of two add-ins will be described in detail. A. Add-in in SolidWorks Solidworks provides a COM interface to access its CAD system. The add-in traverses the entire structure of the CAD model. It gets a hierarchical relationship according to the CAD model, which contains three types of components in general, including assembly, sub-assembly and the part. The assembly component consists of sub-assembly and part components. The sub-assembly should include a part component at least. And the part is the basic component. Among the three types of components, each has its original frame. Eq.1 formulates the hierarchical relationship of the point position in the base frame, as shown in Fig.6.

Fig. 4. One example for a coordinate system mapping to a robot target reference

With the CAD model importing into CAR software, the geometric objects will be extracted and converted into robot program objects for robot programming or simulation automatically. As a result, some advantages can be obtained as the following sections described. Once the CAD model is changed or redesigned, with the basic functionality of common CAD software, the geometric objects defined before will be updated automatically according to the linked geometric features. With these newborn or modified geometric objects, it is easy to import them into the robot simulation tool and update the robot program objects in a simple way, avoiding creating or modifying them repeatedly without value adding.

X BP

TBA T AS X SP

(1)

where,

X BP is the point position in base frame; TBA is the homogeneous transmission matrix from the assembly frame to the base frame;

In the opposite direction, during the programming or simulation phase, some robot program objects, which are coupled with CAD model, should be modified according to the engineering requirement. The robot simulation engineer can export the CAD model with the modified information. When the CAD model is imported into the CAD software, this method will extract such modified information and convert them into geometric objects. Based on these objects, the mechanical designer can do some modification for the CAD model.

T AS is the homogeneous transmission matrix from the subassembly frame to the assembly frame;

X SP is the point position in sub-assembly frame. Reference point frame

Sub assembly frame

After several rounds of modification, a satisfactory mechanical design and robot simulation will be achieved with a high efficiency. Fig.5 illustrates the diagram of this process. Base

Assembly frame

Fig. 6. Hierarchical relationship of the point position in the base frame

Fig.7 illustrates the user interface for add-in in Solidwoks. The left side of Fig.7 shows the structure diagram of the opened CAD model. And the original defined reference coordinate systems are extracted as well. After the reference coordinate systems are selected and transferred into the right side of Fig.7, the mechanical engineer can define which reference coordinate systems will be used as robot targets and

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which ones will be served as robot work objects. After all of the definition is fixed, an intermediate file can be exported from this add-in. This file will be imported into a CAR software in next phase.

Fig. 8. Add-in in RobotStudio

Furthermore, not only the geometric information is useful between CAD and CAR software, but also some other information can be shared between them. For example, assembly sequence is an inherent property for any assembly model and it defines how to assembly this CAD model in a specified order with other models. Once the CAR software gets this information from CAD software, the robot path sequence can be defined directly. If the sequence is not reasonable for robot motion, CAR software can propose a valid sequence and feedback to CAD software. Later a rational assembly sequence will be fixed in CAD and CAR software.

Fig. 7. Add-in in SolidWorks

B. Add-in in RobotStudio As a general platform for ABB robots, RobotStudio offers powerful API (Application Program Interface) to develop customized add-in.

IV.

CONCLUSIONS

With the COM and .NET technique, it is easy to set up an efficient bridge between CAD and CAR software. This collaborative method makes full use of the advantages of the CAD and CAR software and realizes the following improvements for implementation of robotic application:

Depending on the imported intermediate file, which comes from the add-in in Solidworks, the hierarchical and spatial relationship among robot targets and work objects will be fetched. With matrix calculation and RobotStudio API, the new robot targets and work objects can be created in RobotStudio. Later the robot paths will be generated from the robot targets and work objects. Finally the offline programming and simulation will be very easy. Usually the robot simulation engineer can verify the robotic application in a short time.

1) High efficiency for design and simulation: Saving effort and timing cost in today’s robot engineering process by avoiding iterative rounds of CAD model and robot programming modification in low efficiency, achieving solutions of robotic application in short leading time. 2) Seamless engineering workflow: With the intermediate file as a channel, the CAD and CAR software are integrated into a unified engineering platform. It is a huge improvement compared with the traditional engineering procedure.

If the generated robot targets or work objects are not matched with the requirements of robotic application, the robot simulation engineer can modify them until the simulation is qualified. The modification information will be recorded by the add-in in RobotStudio. It can be exported as an intermediate file as well. This file has the similar format with the previous one and some new data are appended into this file.

3) Easy and accurate communication between engineers: Intermediate file between CAD and CAR software makes mechanical engineer and robot simulation engineer communicate much more easily and accurately compared with the traditional method. Although the background of the engineers are different, the formatted intermediate file can fill the gap.

In the opposite direction, the mechanical engineer can import the appended intermediate file into add-in in Solidworks and the modified data are updated into the CAD model. With powerful functionality of Solidworks, the CAD model can be modified automatically according to the modified data.

The approach has proved to have more productivity in several real robotic cases of small part assembly fields. And it frees the engineers from time-consuming check-and-change design loop and improves the engineering efficiency.

Fig.8 presents the user interface for add-in in RobotStudio. The left side of Fig.8 displays the imported information from the previous intermediate file, which comes from the add-in in Solidworks. After clicking ‘Create WorkObject/Target’ button, the corresponding objects will be generated in the RobotStudio. The right side demonstrates the new created program objects for robot programing and simulation.

ACKNOWLEDGMENT The authors would like to thank Dr. Hui Zhang and Dr. Yonglin Chi from ABB Engineering (Shanghai) Ltd for their helpful comments and suggestions.

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[5]

R. Sam, K. Arrifin, N. Buniyamin, “Simulation of pick and place robotics system using Solidworks Softmotion”, System Engineering and Technology, pp.1-6, 2012 [6] http://en.wikipedia.org/wiki/AutomationML [7] https://www.automationml.org/o.red.c/home.html [8] R. Drath, A. Luder, J. Peschke, L. Hundt, “AutomationML- the glue for seamless automation engineering”, Emerging Technologies & Factory Automation, pp.616-623, 2008 [9] R. Drath, “Let’s talk AutomationML what is the effort of AutomationML programming?”, Emerging Technologies & Factory Automation, pp.1-8, 2012 [10] Bernd Kuhlenkoetter, Adrian Schyia, Alfred Hypki, Volker Miegel, “Robot workcell simulation with AutomationML support – An element of the CAx-Tool chain in industrial automation”, Robotics, pp.1-7, 2010 [11] A. Luder, N. Schmidt, S. Helgermann, “Lossless exchange of graph based structure information of production systems by AutomationML”, Emerging Technologies & Factory Automation, pp.1-4, 2013

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