Control of the servo motor was obtained by manipulation of a 3-phase motor controller which could be programmed to specify the motor's modes of operation, and output and input parameters. I set up the motor controller to read an analog voltage as a velocity command, and scaled the input accordingly to translate into the proper linear velocity. The downsides of this control mode were quickly evident, as the data acquisition device sending the voltage only had the range of 0-5v. I set the controller to offset incoming voltage by 2.5v so signals with less than 2.5v resulted in reverse motion, and signals larger than 2.5v resulting in forward motion. This offset caused a variable “noise” element to the signal, which allowed the system a slight amount of drift. Since wave functions predominantly represent displacement, it is advantageous to avoid velocity mode, and control the system in absolute position mode. As of the time of this report, I am currently working on integrating a new data acquisition device which supports the motor controller's position mode, and has the capability to read the motor's encoder signal (so actual position and intended positions can be monitored and calibrated in the user control program.)

The travel of the paddle is governed by two open loop limit switches which stop servo motion when the loop is closed (i.e. the paddle contacts the switch). The limit switches are set up in conjunction with the direction of travel, and the forward motion switch will only limit the motor when the switch is closed and the motor is receiving a forward command. These switches are a secondary safety measure to prevent mechanical over-travel.

y utilizing the motor controller's interface, I programmed the motor to fault upon reaching a torque of 0.8 times the motor's torque rating. The motor is also set to fault if a velocity command of greater than 2000rpms is met. These precautions are to mitigate the damage of a user programming error given to the controller in analog voltage.

Jordan Read (2006)