# Glossary

**Action bit**
:   A bit of the move command: 1 carries out the move, 0 leaves the gripper idle 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 drivers use.

**Coupler connector**
:   The round part on the back of the body that mounts the gripper: one for PAROL6, one for PAR6, a UR5 adapter
    plate, and a template for your own flange.

**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. It limits grip force; the conversion to newtons depends on the motor and mechanism. See
    [Force and speed](https://docs.source-robotics.com/SSG48-gripper-docs/2/03-technical-data/force-and-speed/) for the ideal model and measurement limits.

**Driver**
:   The Spectral Micro board inside the body: 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 motor's current as a vector relative to the rotor, from the driver's encoder. It gives a
    brushless motor a known, limited torque at standstill, which is what makes a force-controlled gripper out of
    it.

**Fin-ray finger**
:   A finger whose two flexible sides are joined by ribs, so that it bends around an object pressed into it. The
    repository has printable ones for the jaw plates.

**Firmware release**
:   One build of the Spectral firmware, numbered 101, 104, 105, … and tagged `v101`, `V104`, `V105`, … in the
    driver's repository. `#Info` prints 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 motor (`#Cal`): the resistance and inductance measured, the pole pairs
    found, 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 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 40 to 80000 encoder ticks per second of the motor.

**Stroke**
:   How much the distance between the jaw plates changes from fully open to fully closed: 48 mm. 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.