Industrial robots have experienced rapid technological development over the past few decades. Since the 1980s, they have evolved from pick-and-place robots, which were merely able to follow a predefined trajectory with limited accuracy, to systems that feature precisions high enough to find applications in operating theatres and that can flexibly adapt to their environments while often interacting with vision systems and other robots in the same production cell. This is why when a 20-year-old Mitsubishi Movemaster robot was found in the stores of a department at Imperial College of London, the first idea was to give it to a museum. One faculty member, however, decided to give Jonas Neubert, an undergraduate student at Imperial College at the time, an opportunity to revive it.
DESIGN OPTIONS: After students tried to reverse-engineer the robot, they needed to define an overall system layout through two main steps. First, they had to develop an I/O solution to drive the robot's five dc motors and concurrently read its encoder signals. Secondly, they needed to find a way to transmit information to a standard PC and display it in a GUI. The students selected National Instruments' CompactRIO programmable automation controller (PAC) for its ability to sample and process the required number of signals concurrently in real time. Even though the cost exceeded the budget of a typical undergraduate project, the CompactRIO versatility and ease of use made it feasible. Because the students could setup the CompactRIO controller (including wiring and deployment of all software) in less than five minutes, they could share one controller with another.
SIGNAL I/O: The field-programmable gate array (FPGA) backplane of the CompactRIO controller enabled the reading, writing and processing of I/O module channels in a truly parallel fashion. With the ample amount of programmable gates, they could output five independent PWM signals with a 1-kHz period and 10 further digital outputs to external motor driver chips, while sampling 10 encoder channels at 100 kHz. Also on the FPGA, they processed the signals from two encoders per robot joint into an integer reading representing the relative joint angle. Using pre-written VIs available on National Instruments' website helped them further shorten the FPGA VI development time.
GRAPHICAL USER INTERFACE: With the event-driven interface, the user can set the location and orientation of the robot end effecter in Cartesian coordinates both by entering a position vector and by moving the robot up/down, left/right and forward/back incrementally. A coordinate transformation is then made and the desired joint angles for each robot joint are computed. These are then fed into a controller subVI that computes the motor demand signals from desired and actual joint angles. As an undergraduate, Neubert developed the entire system, including the software and hardware, in less than nine months of part-time project work.