Remote control of a pneumatic positioning robot.

Ciupe, Valentin ; Maniu, Inocentiu

1. INTRODUCTION

In today's universities and research institutes new learning techniques seem to grow in popularity. The hands-on or learn-by-doing is still the best approach for engineering students working on laboratory exercises--which are perhaps the most powerful learning tools--but this often suffer from lack of accessibility due to location, expenses or complexity. Computer simulations have been used instead of a truly hands-on experience but these are often lacking in the fullness of details that real systems provide. With the advent of high-speed Internet communications an alternative approach to providing hands-on experiences has become possible--remote operation of real equipment. Such remote operation experiences are fully learn-by-doing with nearly all the positive and negative aspects of true hands-on laboratory work. The paper approaches this method by combining pneumatic positioning knowledge with remote control and monitoring.

2. SYSTEM LAYOUT

The robotic cell that executes "pick and place" type operations is built around a three-axes Cartesian pneumatic positioning assembly (robot) custom built by FESTO and two storage spaces (vertical and horizontal) that can hold up to 9 round plastic pieces each. All axes are identical in design and functioning, although slightly different in construction assembly. Figure 1 represents the layout of one axis which comprises the linear drive (1) which essentially is a rodless pneumatic cylinder of DGP-X type.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

A positioning transducer (2) is fitted inside the cylinder and sends data to the SPC-AIF axis interface (4). This is daisy-chained to the others axis interfaces of the system and eventually connected to the SPC200 positioning controller. Two hydraulic shock absorbers (3) are fitted on the both ends of the cylinder in order to prevent damage to the drive in the event of end movement. The cylinder is driven by a proportioning valve of type MPYE-5-X (5) which in turn receives commands from the axis controller over the connecting bus. The compressed air is fed to the valve from a compressor (7) and through an air preparation unit (6) which filters it and regulates the pressure to 6 bars (Festo, 2005).

Besides the positioning axes, the robot also has en end-effector designed as a two-position gripper. A 90[degrees] semi-rotary actuator is used that can orient the gripper towards the vertical or horizontal storage space in order to grab a piece.

For a better understanding of the system, figure 2 represents a 3D model of the robot, with the storage spaces in place (Verzes & Visnyei, 2009).

3. THE SERVER-SIDE APPLICATION

In order for the positioning system to be remotely controlled, a server computer is required. This computer has two main roles: to accept the client's requests and pass those to the PLC in the form of string of positioning commands and to feed back to the client two live video streams about what happens and also some of the PLC's responses.

The server application by itself is constructed as a custom package using Visual Basic. This approach was chosen due to the fact that it can use in the same program Ethernet communication routines and serial communication routines.

The live video feed is insured by a separate application that can push two video streams simultaneously, as a (separate) web server (Webcamxp, 2009). Given the fact that control of the robot is limited only to selected users and by means of the client application, the video streams from the two cameras are unrestricted and a simple webpage was also designed to allow everyone to view the positioning in progress.

The server is also designed to allow only one user at a time to control the robot and with a time limit of 2 minutes (it builds a queue based on user logon time). Users log onto the server using the provided username and password.

From the point of view of the serial commands transmitted to the robots PLCs, the server application translates request strings received from the client into positioning commands accepted by the robot's PLC (Yang et al., 2005).

Another job of the server is to initialize the positioning parameters of the robot in such way that it moves smoothly and without hick-ups. This means setting a trapezoidal velocity profile for all axes and a travel speed of 0.3 m/s (30% of the maximum speed). The positioning precision of the robot's axes is set to +/- 0.5mm, this offering a fast positioning time with sufficient precision for this job.

Every location of the two storage spaces has well defined spatial coordinates relatively to the robot gripper's position. In order to reach such a position all three axes must be positioned using serial formatted strings. This contains the axis number (1<z>, 2<y> or 4<x>), the command itself (C7, C9 ...), the absolute value to be reached (50-449 mm) and the string terminator ([??]). An example of such string is given below:

Code: 1C7+250.00M[??]

Also the controller must receive commands for operating the end effector (opening, closing or rotating the gripper). For every command received, the controller responds, this allows interrogating the current position of the robot at any given time.

After each successful string of commands, the server automatically drives the robot into its "Home" position, selected in such a way that it allows for a full field view from the fixed camera of both storage spaces. This homing routine is represented in figure 3 (Verzes & Visnyei, 2009).

4. THE CLIENT-SIDE APPLICATION

The client software application is designed in such a way that it offers all the main functions in a single window space (figure 4). There are three main areas active at any given time: left frame shows the live feed from the fixed camera (top) and from the end efector camera (bottom); right frame contains the view of the piece vertical and horizontal storage spaces, and the list of commands to be executed; lower frame contains utility buttons and also informations about the ability to control the robot. A progressbar indicates the remaining time once the user has the right to issue positioning commands (Ciupe et al., 2005). Once the user has the right to control the robot, the list of commands can be sent for execution to the server.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

5. FUTURE RESEARCH

In order to ensure a flawless functioning of the system, an electrically operated valve must be placed between the compressor and the air preparation unit, to stop the air consumption when the robot is not in use (home position, waiting for user input etc), as the proportional valves leak air at a rate of 15-16 l/min each, draining the compressor in vain.

A future development of the client software application is considered, that can enhance the control level over the robot, allowing manual positioning anywhere in the workspace of the robot for better understanding of the positioning procedures.

6. CONCLUSION

The motivation for the work described in this paper relates to supporting the remote control of laboratory systems and conducting remote exercises through internet enabled applications that allow students to connect to the lab at almost any time from almost every place. The major requirement for the success of remote experiments has been identified in providing sufficient feedback to the user. Live video is the preferred method for action validation and provides the perceived responsiveness. After an initial familiarization with the system most students are able to accustom to the control method and the general perception is positive.

7. REFERENCES

Ciupe, V.; Maniu, I. & Grigorescu, S. (2005). Internet-based visualization and control of a flexible modular production system, Proceedings of RAAD'05, pp 102-105, ISBN: 973718-241-3, Bucharest, may 2005

Verzes, I. & Visnyei, R. (2009). Pneumatic robot for pick and place applications (undergraduate thesis), UPT, Timisoara

Yang, Y.; Wu, C. & Hu, X. (2005). Study of Web-based integration of pneumatic manipulator and its vision positioning, Journal of Zhejiang University Science, Vol.6A, No.6, pp 543-548, ISSN: 1009-3095

*** (2005). Smart positioning controller manual type SPC200, Festo AG & Co. KG, pp.397, Manual: 170246, Esslingen

*** (2009) http://webcamxp.com--Webcam monitoring, recording and streaming software, Accessed on: 2009-05-29