Robotics
Incipient slip
Definition
Incipient slip is the onset of local sliding within a contact patch while another part of the patch still sticks. Detecting it can warn a robot before gross slip causes an object to move, but the signal depends on contact mechanics, sensor resolution, and detection latency.
Also known as: Partial slip onset
Updated
Slip begins locally before an object slides away
Tangential load is not always distributed uniformly across a finger-object contact. Regions near the edge can start sliding while an inner region remains stuck. This partial transition is incipient slip. Gross slip follows when the remaining sticking region can no longer maintain the contact.
The distinction matters because object motion or a large change at a force-torque sensor may arrive after useful warning time has been lost. High-resolution tactile sensing can instead look for local deformation or motion patterns inside the contact patch.
Regulate grip before gross slip
Dong and colleagues estimated a dense slip field from GelSlim tactile images by comparing observed imprint motion with a two-dimensional rigid transformation. They reported detecting translational and rotational incipient slip at 24 Hz, with 86.25 per cent accuracy over 240 trials on ten objects, and used the feedback in bottle-cap experiments. These are results for their sensor, assumptions, objects, and procedure.
A gripper can respond by increasing normal force, changing wrist motion, or slowing a manipulation. Tactile servoing can use the warning as feedback while avoiding unnecessarily high grip force that could damage a fragile object.
The warning is contact and sensor dependent
The cited method assumes a mostly rigid object and interpretable motion of a soft tactile imprint. Deformable, textured, wet, or rolling contacts may produce different fields. A detector trained or tuned for one sensor skin, sampling rate, and contact geometry may not transfer to another.
Incipient-slip detection does not establish force closure, identify the cause of motion, or guarantee recovery. Computation and actuator delay can turn an early signal into a late response. Robots should combine it with force limits, object-motion estimation, and a fallback for contacts that have already entered gross slip.
Sources
Related terms
Tactile sensing
Tactile sensing measures information arising from physical contact, such as contact geometry, deformation, or force. Robots use it to observe interactions at their fingers, grippers, feet, or other contact surfaces.
Tactile servoing
Tactile servoing is closed-loop robot control that uses tactile measurements to reduce error relative to a desired contact state. The feedback may represent contact pose, pressure, shear, a raw tactile image, or a learned tactile feature.
Force closure
Force closure is a contact condition in which the admissible contact wrenches can collectively oppose any external wrench direction on an object. The condition depends on contact locations, normals, and the assumed friction model.
Force-torque sensor
A force-torque sensor is a transducer that measures forces and moments applied through a robot interface. A common six-axis sensor reports three force components and three torque components as a wrench in the sensor's coordinate frame.