Nodes to control and test the inter-pupillary rail stepper

Nodes :

• stepper_controller : Control the stepper motor by issuing commands to this node. The commands are listed below.

Stepper Controller node

Start node:

rosrun stepper_controller stepper_controller_node.py

This node listens to publishers on:

• /motor/inter_eye/command : issue commands to the stepper motor. The motor will also publish useful state information such as when it hits a limit switch.

The launch file will simply start the node:

roslaunch stepper_controller stepper_controller.launch

Messages format

The messages are encoded in JSON. Each message represents a command to run on the stepper motor.

run command

{
    "command" : "run",
    "parameters" : {
        "direction" : "clockwise",
        "speed" : 800.0
    }
}

direction (string)

Used to indicate the direction of the rotation:

• clockwise: the stepper will run in a clockwise direction
• counter-clockwise: the stepper will run in a counter-clockwise direction

Using a different direction name will result in the command being ignored.

speed (float)

Used to indicate at which speed the stepper will run. This value should be between the configured MIN_SPEED (default 0 step/s) and MAX_SPEED (default 991.8 step/s). Otherwise, the stepper's speed is clamped to one of these values.

move command

{
    "command" : "move",
    "parameters" : {
        "direction" : "clockwise",
        "steps" : 450
    }
}

direction (string)

Used to indicate the direction of the rotation:

• clockwise: the stepper will run in a clockwise direction
• counter-clockwise: the stepper will run in a counter-clockwise direction

Using a different direction name will result in the command being ignored.

steps (int)

Used to indicate the number of microsteps by which the stepper will move. The steps value is in agreement with the selected step mode; the parameter value unit is equal to the selected step mode (full, half, quarter, etc.).

goTo command

{
    "command" : "goTo",
    "parameters" : {
        "position" : 680
    }
}

position (int)

Used to indicate at which position the stepper will go to. Note that the position value is always in agreement with the selected step mode; the parameter value unit is equal to the selected step mode (full, half, quarter, etc.).

stop command

{
    "command" : "stop",
    "parameters" : {
            "type" : "soft"
    }
}

type (string)

Used to indicate the type of stop to apply to the stepper:

• hard: the stepper will stop immediately
• soft: the stepper will stop after a deceleration as configured by the DEC register

Using a different stop type name will result in the command being ignored.

SPI Notes :

The SPI device consisting of the stepper can be either /dev/spidev0.0 or /dev/spidev0.1. This has to be modified accordingly in:

stepper_controller/src/stepper_controller_node.py