hybrid position/force control
Hybrid position/force control is a way of telling a robot arm to be picky about position in some directions and picky about pushing force in others — at the very same moment. Think about wiping a table with a sponge. Side to side and forward, you care exactly where the sponge goes, so you control its position. But straight down into the table, you do not want a precise height — you want a gentle, steady press, so there you control the force instead. A robot doing this same job needs both rules running together, each pointing in a different direction.
The trick is to split the directions of the task into two groups. Some directions are 'position-controlled': the robot is told a target spot and works hard to land the tool exactly there, ignoring how much force that takes. The other directions are 'force-controlled': the robot is told a target push and adjusts its motion to keep that push steady, ignoring exactly where the tool ends up. A piece of math called a selection mask marks which directions belong to which group, so the two controllers never fight over the same axis.
This matters whenever a robot must touch a surface it cannot perfectly measure, like grinding a weld, turning a crank, or sliding a peg into a hole. Pure position control would crack the part or snap the tool the instant reality differs from the plan by a hair; pure force control would let the tool wander off the path. Splitting the task lets the robot stay exactly on track where it must and stay gentle where it must, all at once.
A robot deburring a metal plate moves the grinding tool along the edge with position control, while pressing into the plate with a constant force, so it follows the shape exactly yet never gouges too deep.
Position along the edge, force into the surface — two rules, two directions, one motion.
The two groups must be 'complementary': a direction is either position-controlled or force-controlled, never both, so the robot is never given two conflicting orders along the same axis.