RoboteQ AX500 manual Position Sensor Selection, Sensor Mounting, Closed Loop Position Mode

Closed Loop Position Mode

Position Sensor Selection

The AX500 may be used with the following kind of sensors:

•Potentiometers

•Hall effect angular sensors

The first two are used to generate an analog voltage ranging from 0V to 5V depending on their position. They will report an absolute position information at all times.

Sensor Mounting

Proper mounting of the sensor is critical for an effective and accurate position mode opera- tion. Figure 35 shows a typical motor, gear box, and sensor assembly.

Position Feedback

Position Sensor

Gear box

FIGURE 35. Typical motor/potentiometer assembly in Position Mode

The sensor is composed of two parts:

•a body which must be physically attached to a non-moving part of the motor assem- bly or the robot chassis, and

•an axle which must be physically connected to the rotating part of the motor you wish to position.

A gear box is necessary to greatly increase the torque of the assembly. It is also necessary to slow down the motion so that the controller has the time to perform the position control algorithm. If the gearing ratio is too high, however, the positioning mode will be very slug- gish.

A good ratio should be such that the output shaft rotates at 1 to 10 rotations per second (60 to 600 RPM) when the motor is at full speed.

The mechanical coupling between the motor and the sensor must be as tight as possible. If the gear box is loose, the positioning will not be accurate and will be unstable, potentially causing the motor to oscillate.

Some sensor, such as potentiometers, have a limited rotation range of typically 270 degrees (3/4 of a turn), which will in turn limit the mechanical motion of the motor/potenti- ometer assembly. Consider using a multi-turn potentiometer as long as it is mounted in a

64 AX500 Motor Controller User’s Manual Version 1.9b. June 1, 2007