force

force.py

Overview

force.py is a synthetic end-effector force sensor that publishes pseudo-random force readings so that grasp controllers, compliant planners, and safety monitors can be developed and tested without real hardware.

Interfaces (strongly-typed, stateless)

Direction	Topic	Semantics
Provided	/{robot}/force	std_msgs/Float32 – simulated contact force in Newtons

Contract

Pre-conditions

• Node launched with a valid robot_id CLI argument.

• Downstream nodes subscribe to /force at ~10 Hz.

Post-conditions

• Publishes one Float32 message per loop iteration.

• data field is a float uniformly drawn from [0, _MAX_FORCE].

Invariants

• Loop frequency = _RATE ± ROS scheduler jitter.

• Force range fixed by _MAX_FORCE.

Quality-of-Service KPIs

Metric	Target	Rationale
Message rate	10 Hz ± 0.5 Hz	Ensures smooth controller input.
Latency	< 100 ms	Prevents stale force readings.
CPU load	< 1 %	Safe on embedded CPUs.

Implementation notes

• Uses random.uniform(0, _MAX_FORCE) for force generation.

• All logic in force_sensor(); the loop maintains timing.

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

Functions

force_sensor()

Initialise ROS publisher and broadcast random force values until shutdown.