encoder_gripper

encoder_gripper.py

Overview

encoder_gripper.py is a dummy gripper-position sensor that publishes pseudo-random gripper opening widths at a fixed rate. It enables PID loops, dashboards and loggers to run when the physical gripper is offline or during CI.

Interfaces (strongly-typed, stateless)

Direction	Topic	Semantics
Provided	/{robot}/encoder_gripper	std_msgs/Int32 – simulated gripper opening width in mm (0–100)

Contract

Pre-conditions

• Node launched with a valid robot_id CLI argument.

• Subscribers expect gripper widths at ~10 Hz.

Post-conditions

• Publishes exactly one Int32 per loop iteration.

• data field is an integer uniformly drawn from [0, _MAX_WIDTH].

• No internal state retained beyond the RNG.

Invariants

• Loop frequency = _RATE ± ROS scheduler jitter.

• Width range fixed by _MAX_WIDTH.

Quality-of-Service KPIs

Metric	Target	Rationale
Message rate	10 Hz ± 0.5 Hz	Keeps gripper controllers in sync.
Latency	< 100 ms	Prevents stale position readings.
CPU load	< 1 %	Safe on embedded CPU.

Implementation notes

• Uses random.randint(0, _MAX_WIDTH) for uniform width generation.

• All logic is in gripper_encoder(); the main loop maintains timing.

• Seed the RNG (random.seed(…)) before calling for reproducible tests.

Functions

gripper_encoder()

Initialise ROS publisher and broadcast random gripper widths until shutdown.