User Manual

Table Of Contents
Closed Loop Relative and Tracking Position Modes
146 Advanced Digital Motor Controller User Manual V2.0 July 8, 2019
Selecting the Position Modes
The two position modes are selected by changing the Motor Control parameter to Closed
Loop Position. This can be done using the corresponding menu in the Power Output tree
in the Roborun utility. It can also be done using the associated serial (RS232/RS485/TCP/
USB) command. See “MMOD” on page 310. The position mode can be set independently
for each channel.
Position Feedback Sensor Selection
The controller may be used with the following kinds of sensors:
Potentiometers
Hall effect angular sensors
Optical Encoders
Hall sensor in brushless motor
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.
Modern position Hall sensors output a digital pulse of the variable duty cycle. These sen-
sors provide an absolute position value with high precision (up to 12-bit) and excellent
noise immunity. PWM output sensors are directly readable by the controller and therefore
are a recommended choice.
Optical encoders report incremental changes from a reference which is their initial posi-
tion when the controller is powered up or reset. Before they can be used for reporting po-
sition, the motors must be moved in open loop mode until a home switch is detected and
resets the counter. Encoders offer the greatest positional accuracy possible.
Sensor Mounting
Proper mounting of the sensor is critical for an effective and accurate position mode oper-
ation. Figure 11-1 shows a typical motor, gear box, and sensor assembly.
Position Sensor
Gear box
Position Feedback
FIGURE 11-1. 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 as-
sembly or the robot chassis, and
an axle which must be physically connected to the rotating part of the motor you
wish to position.