Glossary¶
- Action bit
- A bit of the move command: 1 carries out the move, 0 stops the move and holds the jaws still, with the command stored. The action status of the answer repeats this bit.
- Activated
- A flag the gripper keeps, set by the activate bit of the move command or by
#Gripact. A move is carried out only while the gripper is activated and calibrated. - CAN ID (node ID)
- The address of the gripper on the CAN bus, 0 to 13; every gripper ships as 0. It occupies bits 10 to 7 of the 11-bit CAN frame identifier; the command ID occupies bits 6 to 1 and the error bit is bit 0.
- CANvas
- Source Robotics' USB-to-CAN adapter. It appears as a serial port and speaks slcan, which
python-can, Motor GUI and the ROS 2 driver use. - Current limit (grip force)
- The current, in mA, the driver may put into the motor during a move. Torque is current times the motor's torque constant, so the current limit sets the force with which the jaws press on an object.
- Driver
- The STEPFOC board on the back of the gripper's stepper: field-oriented control of the motor, the gripper state machine and the CAN and UART interfaces. The gripper's firmware is the driver's firmware.
- E-stop bit
- A bit of the move command. 1 stops the gripper and raises the gripper E-stop error, which comes back at every cycle while the last command's bit is 1: send a command with the bit at 0, then clear the error.
- Error bit
- Bit 0 of every CAN frame identifier the driver sends: 1 while any error is active.
- Field-oriented control (FOC)
- Controlling the stepper's current as a vector relative to the rotor, from the driver's encoder. It turns the stepper into a motor whose torque is known and limited, which is what makes a force-controlled gripper out of it.
- Firmware release
- One build of the STEPFOC firmware, numbered 103, 104, 105, … and tagged
V103,V104, … in the driver's repository.#Infoprints the release a gripper runs. This documentation describes one release; the version selector switches between them. - Gripper calibration
- The routine (
Send_gripper_calibrate,#Gripcal) that opens the jaws fully, then closes them fully, at low force, and records both end stops as positions 0 and 255. Needed after every power-up. - Gripper mode
- The driver's mode in which it runs a gripper (
#Gripper 1, saved): move commands with a jaw position, a speed and a current limit, and object detection. - Motor calibration
- The driver's own calibration of the stepper (
#Cal): the pole pairs, resistance and inductance entered, the encoder aligned, the motor constants measured. Done once, at the factory or when you build the gripper; not to be confused with the gripper calibration. - Object detection
- The gripper's report of why the jaws stopped: 0 still moving, 1 an object stopped them while closing, 2 an object stopped them while opening, 3 they reached the commanded position.
- Position
- The jaw position as the gripper commands and reports it: 0 fully open, 255 fully closed, linear in between.
- Rack and pinion
- The gripper's mechanism: a pinion on the motor shaft meshes with two racks that run on the linear rail in opposite directions, so one motor moves both jaws symmetrically.
- Speed
- The speed of a move, 0 to 255, mapped by the firmware to 500 to 60000 encoder ticks per second of the motor.
- Stroke
- How much the distance between the jaw carriers changes from fully open to fully closed: 55, 105 or 155 mm, set by the rail length. Each jaw travels half of it.
- Timeout error (watchdog)
- The driver's CAN watchdog, as the gripper reports it: when the watchdog is set (
Send_Watchdog) and no gripper command or status request arrives in time, the gripper stops and raises it. - Watchdog
- A timer the driver resets with every gripper command (full or empty) and every status request it receives. When it is set and runs out, the gripper reports a timeout error and stops.
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