Saturday, April 2, 2016

Controlling DC motor by means of direction of rotation and torque/power insertion

For running a DC motor in both direction (in our case CRS Robotics gripper) you need to have a bridge to be able to switch the polarity of the source. For this purpose I have used  EVAL6206PD board which not only provides a protected bridge but also it has PWM current control for both of its output independently.

The two bridges are designated A and B and their output pins designated as OUT1A, OUT2A, OUT1B, and OUT2B. These outputs are controlled independently by logic inputs IN1A, IN2A, IN1B, and IN2B respectively.

A logic high or low on any of these inputs will drive its corresponding output to the positive supply rail or to ground. Both of the A outputs will be forced to an off (high impedance) state if the ENA pin is taken logic low, as will the B outputs if ENB is taken low. Each bridge also has an analog control signal, VREFA and VREFB, which control the current.

The truth table is as follows:

INPUTS                        OUTPUTS
EN IN1 IN2                  OUT1      OUT2
L    X     X                     High Z     High Z
H    L     L                     GND        GND
H    H     L                     Vs            GND
H    L     H                     GND        Vs
H    H     H                     Vs            Vs

X = Don't care
High Z = High Impedance Output

Schematic for this driver can be downloaded from here:

The CRS gripper has a potentiometer (for position) and a DC motor: