2363 tote stacker prototype

[ToddF]

Originally Posted by thatprogrammer

What is the disk break doing in this mechanism?

Brakes in a mechanism such as this are used to conserve energy and reduce the power consumption to the motor. If you use position feedback on the elevator, such as an encoder, you can use a PID control loop to hold position. Some of the approved motor controllers have microprocessors that can do the PID control right in the motor controller. Or, if you want, you can have the PID control loop happen onboard the robot RIO. Running the control loop on the motor controller offloads that computing power from the RIO.

The control loop applies current to the motor to drive the position of the elevator to the commanded position. If the elevator is very lightly loaded, it takes very little current to hold the elevator in position. The new interface tools to the robotRIO allow you to monitor the current the motor is drawing. As the load on the elevator increases, it takes more and more current to hold the elevator in position. With a full stack of totes, this could drain your battery more quickly, and can also cause your motor to heat up. If you have a mechanical brake on your system, you use the PID controller to quickly drive the elevator to the desired position. Then, you engage the brake and disable the PID loop. Now there is no current being sent to the motor. When you want to make a new move, you disengage the brake, make the move with the motor, and then re-engage the brake.

An alternative to using a brake is to choose a drivetrain which has lots of friction when backdriven. This could be a wormdrive gearbox, or just a very high reduction planetary gearbox/chain drive/belt drive combination. The high reduction maintains position even under high external loading. The tradeoff is that the higher the reduction, the slower the motion will be with a given motor. Also, the higher the reduction, the lower the mechanical efficiency of the system. In an industrial application, you might compare the energy lost by a less efficient drivetrain to the energy necessary to actuate the brake.