Force/Torque Sensing

Force/torque sensors enable compliant control strategies like impedance control and admittance control. These allow a robot to behave like a spring-damper system, yielding to contact forces rather than fighting them. This is critical for delicate assembly tasks (e.g., inserting a peg into a hole, screwing components) where geometric uncertainty exists. The sensor provides real-time feedback, allowing the controller to adjust the robot's pose to accommodate misalignments and prevent jamming or part damage.

Precise control of grip strength is essential for handling a wide variety of objects. A force/torque sensor at the wrist or within a dexterous gripper measures the contact forces during a grasp. This feedback allows the robot to:

• Apply the minimum necessary force to securely lift fragile items (eggs, electronic components).
• Detect slip by monitoring shear forces and increase grip to prevent dropping.
• Achieve form closure or force closure by actively adjusting finger positions based on tactile feedback, ensuring stable manipulation.

In shared workspaces with collaborative robots (cobots), force/torque sensing is a primary safety and interaction modality. It enables:

• Physical guidance programming: An operator can directly move the robot arm by applying force, and the sensor records the motion for playback.
• Reactive collision detection: Unexpected contact with a human or obstacle generates a force/torque signature that triggers an immediate protective stop.
• Hand-over tasks: The robot can sense when a human takes an object from its gripper and release its grasp accordingly.

Beyond simple force measurement, these sensors allow a robot to infer the contact state with its environment. By analyzing the wrench (combined force and torque vector), the system can determine:

• If contact is point, line, or surface contact.
• The center of pressure on an end-effector.
• When a part has been seated correctly in a fixture. This information is vital for haptic exploration, where a robot actively probes an object or surface to identify its properties (e.g., stiffness, texture, edges) or locate features by touch.

A force/torque sensor can automatically identify the inertial properties of an unknown payload attached to the end-effector. By executing specific excitation motions and measuring the dynamic forces, the robot can calculate the payload's mass, center of mass, and inertia matrix. This is crucial for dynamic model-based controllers like Model Predictive Control (MPC). Similarly, the sensor is used to precisely calibrate the Tool Center Point (TCP) by touching a fixed point in space from different orientations and calculating the offset.

These material removal tasks require maintaining a constant normal force against a contoured surface. A force/torque sensor provides closed-loop feedback to adjust the robot's trajectory in real time, compensating for part geometric variations and tool wear. This ensures a uniform finish quality. Applications include:

• Robotic deburring of machined metal parts.
• Polishing complex molds or automotive body panels.
• Sanding wooden components. The alternative—rigidly programming the path—often leads to inconsistent results or tool damage.

A robotic control strategy that regulates the dynamic relationship between a manipulator's position and the contact forces it exerts. Instead of tracking a rigid position trajectory, it creates a desired mechanical impedance—modeled as a virtual spring-damper system—at the end-effector. This allows the robot to behave compliantly upon contact, making it essential for tasks like assembly, polishing, or physical human-robot interaction. Force/torque sensors provide the critical feedback to close this control loop.

A control paradigm where measured external forces (from a force/torque sensor) are used to generate a commanded motion. The controller specifies how the robot should move in response to contact, effectively controlling its compliance. It typically uses an outer force-feedback loop to modify the reference trajectory for an inner position controller. This architecture is often used with stiff, high-gear-ratio robots where direct torque control is not feasible, allowing them to perform delicate tasks like insertion.

The measurement of detailed contact properties at the gripper or robot skin, complementing wrist-based force/torque sensing. Tactile sensors measure:

• Pressure distribution across a contact patch
• Shear forces and slip detection
• Vibration and texture
• Temperature This high-resolution, localized data is crucial for assessing grasp stability, manipulating fragile objects, and understanding object properties. It operates at a different spatial scale than a wrist-mounted F/T sensor, which measures the net resultant force.

A robotic strategy for part mating (e.g., peg-in-hole, screw insertion) that leverages force sensing to accommodate uncertainties in part position and robot calibration. Instead of relying on perfectly precise positional accuracy, the controller uses force/torque feedback to detect contact states (chamfer contact, one-point contact, two-point contact) and execute corrective motions like spiral searches. This enables reliable automation without expensive, ultra-precise fixturing and is a classic industrial application of force control.

A unified control framework for complex robots (e.g., humanoids, mobile manipulators) that coordinates all degrees of freedom to execute multiple tasks simultaneously under physical constraints. Force/torque sensing at the wrists or feet is often a critical input. WBC formulates control as a quadratic programming problem that solves for joint torques or accelerations to achieve prioritized tasks (e.g., maintain balance, apply a specific end-effector force, avoid joint limits) while respecting contact force constraints.

The direct, real-time remote control of a robotic manipulator by a human operator. Force-reflective teleoperation uses bilateral control, where the operator's commands move the robot, and forces measured by the robot's force/torque sensor are reflected back as haptic feedback to the operator's control device. This creates a sense of telepresence, allowing the operator to perform delicate tasks like surgery, bomb disposal, or underwater manipulation with enhanced perception of contact forces.