A software controller was implemented for the three-link robot. This controller uses a simple local PID control algorithm, and simulates three PID controllers; one for each link. Several experiments and tests have been conducted using this software to examine the effects of changing some of the control parameters on the performance of the robot.
The control parameters that can be changed in this program are:
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)In these experiments, the program was executed on a Sun SPARCStation-10, and the A/D chip was connected to the serial port of the workstation. One problem we encountered with this workstation is the slow protocol for reading the sensor data, since it waits for an I/O buffer to be filled before it returns control to the program. We tried to change the buffer size or the time-out value that is used, but we had no success in that. This problem causes the update rate to be very low (about 30 times per second), and this affects the positional accuracy of the robot. We were able to solve this problem on an HP-700 machine, and we reached an update rate of 120 times per second which was good enough for our robot.
Figures 49, 50, 51, and 52 show the desired and actual position for different test cases using different feedback gains.
Figure 49: Desired and actual position for test case (1).
Figure 50: Desired and actual position for test case (2).
Figure 51: Desired and actual position for test case (3).
Figure 52: Desired and actual position for test case (4).