Telekinesis Agentic Skill Library

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Move in Force Mode ​

SUMMARY

Move in Force Mode executes compliant robot motion by regulating force and/or torque behaviour during movement.

This skill is designed for force-interaction tasks such as polishing, insertion, constrained guidance, and adaptive contact control.

SUPPORTED ROBOTS

This skill is currently supported on Universal Robots only.

The Skill ​

python
# Called in a 2 ms control loop
robot.move_in_force_mode(
    task_frame=task_frame,
    selection_vector=selection_vector,
    force=force,
    force_mode_type=2,
    limits_speed=limits,
)

The Code ​

Example 1: Apply alternating Z-axis force in a control loop ​

Run a 2000-cycle loop at 2 ms per cycle. The first 1000 cycles push upward along Z; the remaining 1000 push downward.

python
import time
from loguru import logger
from telekinesis.synapse.robots.manipulators import universal_robots

robot_ip = "192.168.1.2"  # replace with your robot's IP

robot = universal_robots.UniversalRobotsUR10E()
robot.connect(ip=robot_ip)

task_frame = [0, 0, 0, 0, 0, 0]
selection_vector = [0, 0, 1, 0, 0, 0]
wrench_up = [0, 0, 20, 0, 0, 0]
wrench_down = [0, 0, -1, 0, 0, 0]
force_mode_type = 2
limits = [2, 2, 1.5, 1, 1, 1]

period = 0.002
start_time = time.perf_counter()

for i in range(2000):
    cycle_start = time.perf_counter()

    wrench = wrench_up if i <= 1000 else wrench_down
    robot.move_in_force_mode(
        task_frame=task_frame,
        selection_vector=selection_vector,
        force=wrench,
        force_mode_type=force_mode_type,
        limits_speed=limits,
    )

    elapsed = time.perf_counter() - cycle_start
    sleep_time = period - elapsed
    if sleep_time > 0:
        time.sleep(sleep_time)

logger.info(f"Force mode completed in {time.perf_counter() - start_time:.3f} s.")
robot.disconnect()

The Explanation of the Code ​

move_in_force_mode applies one cycle of force-controlled motion and must be called repeatedly inside a control loop — typically at 500 Hz (2 ms period). Each call commands the robot controller to apply the specified wrench on compliant axes while holding pose on non-compliant axes.

Task frame. task_frame is a pose vector [x, y, z, rx, ry, rz] defining the frame in which forces and compliance are expressed, relative to the robot base frame. Position in metres; orientation in degrees. Pass [0, 0, 0, 0, 0, 0] to use the base frame directly.

Selection vector. selection_vector is a 6D binary vector where 1 marks a compliant axis and 0 marks a rigid axis. The example [0, 0, 1, 0, 0, 0] makes only the Z axis compliant — the robot moves freely along Z to track the force target while holding its X, Y, and orientation rigidly.

Force. force is a wrench [Fx, Fy, Fz, Tx, Ty, Tz] in Newtons and Newton-metres. The robot adjusts its position on compliant axes to converge toward these values. Values on non-compliant axes are ignored.

Force mode type. force_mode_type controls how the task frame is oriented during motion:

  • 1 — task-frame Y-axis aligns from TCP to force-frame origin
  • 2 — task frame is fixed as defined by task_frame
  • 3 — task-frame X-axis aligns with the projection of TCP velocity onto the task-frame X-Y plane

Limits. limits_speed is a 6D vector of speed limits. On compliant axes it caps TCP speed (m/s for position, deg/s for rotation); on non-compliant axes it caps the allowed deviation from the commanded pose.

How to Tune the Parameters ​

ParameterTypeDefaultDescription
task_framelist[float] or np.ndarray—Force frame pose [x, y, z, rx, ry, rz] relative to base frame. Position in metres; orientation in degrees.
selection_vectorlist[int] or np.ndarray—6D binary vector. 1 = compliant axis, 0 = rigid axis.
forcelist[float] or np.ndarray—Target wrench [Fx, Fy, Fz, Tx, Ty, Tz]. Forces in N; torques in N·m.
force_mode_typeint—Task-frame interpretation: 1 Y-aligned, 2 fixed, 3 velocity-aligned. Integer in [1, 3].
limits_speedlist[float] or np.ndarray—6D speed limits. Compliant axes: max TCP speed (m/s or deg/s). Non-compliant axes: max pose deviation (m or deg).

Choosing limits

Start with conservative speed limits (e.g. 1.5 m/s on the compliant axis) and tighten them for delicate tasks. Loose limits allow larger motion excursions, which can cause unexpected collisions.

WARNING

move_in_force_mode must be called at a consistent rate (typically 500 Hz / 2 ms period). Irregular call timing can cause jerky motion or controller faults. Ensure your control loop maintains the required period.

Where to Use the Skill ​

  • Surface following — Maintain constant contact force while tracking a curved surface (e.g. polishing, deburring)
  • Compliant insertion — Guide a part into a socket with controlled insertion force to handle positional errors
  • Constrained guidance — Allow the environment to deflect the robot on compliant axes while holding pose on rigid axes
  • Force ramp-up — Gradually increase applied force to seat a component without impact

When Not to Use the Skill ​

Do not use Move in Force Mode when:

  • Only a single contact event is needed — use Move Until Contact to approach and stop on contact without running a continuous loop
  • Precise positioning is the goal — force mode trades position accuracy for force compliance; use Set Cartesian Pose for position-controlled moves
  • The task does not require force regulation — force mode adds complexity and safety risk; only enable it when force control is genuinely needed