Controlling a one-link robot in a real-time manner is not too difficult, but on the other hand it is not a trivial task. This is the basis of controlling multi-link manipulators, and it gives an indication of the type of problems and difficulties that might arise in a larger environment. The idea here is to establish a complete model for controlling and simulating a one-link robot, starting from the analysis and design, through the simulation and error analysis.
A motor controlled by PID controller was used with an analog I/O card, named PC-30D, connected to a Hewlett Packard PC. This card has sixteen 12-bit A/D input channels, two 12-bit D/A output channels. There are also the card interface drivers with a Quick BASIC program that uses the card drivers to control the DC motor.
One of the problems we faced in this process is to establish the transfer function between the torque and the voltage. We used the motor parameters to form this function by making some simplifications, since some of the motor parameters have non-linear components which makes it too difficult to make an exact model. The transfer function is in the form:
where,
is the voltage at time
.
is the torque at time
.
is the torque from the motor.
.
.
.
several input sequences have been used for the desired trajectories and the actual positions and velocities are measured using a potentiometer and a tachometer. The results were fed to a graphical simulation program which displays the movement of the link, the desired and actual positions, the desired and actual velocity, and the error in position and velocity. The interface window is shown in Figure 4.
In general, This experiment gave us an indication of the feasibility of our project, and good practical insight. It also helped us determine some of the technical problems that we might face in building and controlling the three-link robot. More details about this experiment can be found in [8].
