Robot control
Hybrid position-force control
Definition
Hybrid position-force control regulates motion in some task directions and contact force in complementary constrained directions. It separates the commands according to the motion and force freedoms permitted by the environment.
Also known as: Hybrid motion-force control, Hybrid force-position control
Updated
Assigning motion and force directions
When a robot wipes a rigid tabletop, it can follow a path along the surface while regulating the force pressing into it. The tangential directions allow motion; the normal direction provides a contact constraint. Modern Robotics develops controllers that project motion and force commands into the appropriate task subspaces.
The separation is defined by the contact geometry, rather than by a permanent choice of world axes. Opening a hinged door, for example, has a permitted rotational motion that changes the relevant hand motion as the door swings.
Avoiding conflicting commands
Trying to impose both an exact rigid position and an independent force in the same constrained direction can create incompatible objectives. Hybrid control instead assigns complementary directions to the two controllers. The resulting desired wrench is mapped into joint commands through the Jacobian.
Contact assumptions matter
The textbook formulation assumes known rigid constraints and particular motion freedoms. If the surface position or normal is wrong, or the hand loses contact, the selected subspaces may no longer describe the interaction. Impedance control offers a different way to manage contact by prescribing a compliant force-motion relationship. A practical task may combine these ideas, but they describe different control objectives.
Sources
Related terms
Force control
Force control regulates the force or wrench a robot applies to its environment. It may use a robot model, measured interaction forces, or both to produce joint commands that achieve a desired contact load.
Impedance control
Impedance control shapes the dynamic relationship between a robot’s motion and the forces it exchanges with its environment. A common goal is for the robot to respond like a chosen mass, spring, and damper at a joint or end effector.
Robot Jacobian
A robot Jacobian is a configuration-dependent matrix that maps joint velocities to a chosen task velocity, often an end-effector twist. It describes the local relationship between joint motion and task motion.
End effector
An end effector is the part of a robot positioned to perform a task at the end of a manipulator, such as a gripper, hand, suction tool, or welding tool. Its pose and interaction forces are often the quantities a task controller regulates.