Scara robot

Session 2526

Remote Control of a Robot Using LabVIEW and the World Wide Web
Elaine Cooney, Anna Shiver Electrical Engineering Technology, Indiana University Purdue University Indianapolis

Introduction This paper describes a prototype system to control a robot via the World Wide Web. The user is able to move the robot and view the results through a video camera. National Instruments’LabVIEW software is used to program the system. There are two major goals of this project. The first is to replace DOS based robot controllers with modern motion control hardware and software. Not only does this eliminate the difficulty of finding computers that are capable of communicating with the controllers, but the system is flexible enough to give students experience with many levels of motioncontrol. Students may only use the top level of the application and program the robot in a “teach pendant” mode, or they may read encoders and energize the motors step by step. The second goal is to allow monitoring and control of the robot over the Internet. This may be used for students in a distance education environment, but is also attractive for K-12 demonstrations. LabVIEW 6i makes Webinterface easy, using the DataSocket software (included in LabVIEW) to pass controls and information between the Web application and server. Hardware Description The motion control card is a National Instruments 7344 Motion Controller. It has encoder inputs and control outputs for four axis using stepper or servo motors and four ports of digital I/O. In this project configuration the digital outputs areused to control the motor. Pulse width modulation is used to change the speed of motion. The motion control and digital I/O are on separate connectors, so two cables and connector blocks are needed. (See Figure 1.) Driver circuits for the motors have been designed and built in-house so the robot can be controlled from a variety of sources, including micro controllers and programable logiccontrollers. The driver circuits (one for each axis) converts TTL level signals to +/- 12V, high current signals necessary for the servo motors. The driver circuits also provide connectivity to the encoder and hard home signals. Circuitry on the robot prevents motion past the end of travel switches, and these signals are not available on the cables coming from the robot.

“Proceedings of the 2001American Society for Engineering Education Annual Conference & Exposition Copyright © 2001, American Society for Engineering Education”

Figure 1: Hardware Block Diagram The robot used in this system is a four axis plus gripper Selective Compliance Assembly Robot Arm (SCARA). (See Figure 2.) The shoulder and elbow operate in the x-y plane. The wrist has z movement, as well as theta. The gripper canopen or close. Each of these five motors are servo motors with quadrature encoders and hard home indicators. Software Description The motion controller hardware comes with software to monitor quadrature encoders, home axis, pulse width modulation for speed control, and other high-level controls. This system uses LabVIEW graphical programming language. In most applications, the motion control boarduses a polarized analog output to drive the motor Figure 2: SCARA Robot forward or reverse. But the driver circuit used for this project requires two different digital inputs: one TTL input indicates forward and a separate input is used for reverse. Because this system cannot fully utilize the motion control capabilities of our control board, the motion VI’s have been written from scratch.Development has been kept extremely modular to accommodate possible future changes in system hardware. For instance, a counter-timer board could be used to read the encoders and generate PWM signals, or another motor driver circuit (that can accept analog inputs) may replace the current version. Figure 3 shows the front panel for a simple one axis control. The axis is selected (A, B, etc.) and the...