Workpiece rotating appartus and robot system

A workpiece rotating apparatus comprising:

• a first rotary positioner and a second rotary positioner which are arranged to face each other in a direction along an approximately horizontal rotation axis, and which hold, respectively, one end portion and the other end portion of a workpiece extending parallel to the rotation axis, and which can rotate the workpiece around the rotation axis;
• a linear motor which linearly moves the second rotary positioner in the direction along the rotation axis;
• and
• a motor controller which controls the linear motor to adjust a position of the second rotary positioner in the direction along the rotation axis,
• wherein the motor controller controls the linear motor so that magnitude of force acting on the linear motor from the other end portion of the workpiece via the second rotary positioner becomes smaller than a predetermined threshold,
• wherein the workpiece rotating apparatus further comprises an external force detection unit which detects the force acting on the linear motor from the other end portion of the workpiece via the second rotary positioner, and
• wherein, the motor controller changes a position where the second rotary positioner is held by the linear motor toward a direction with which the force detected by the external force detection unit becomes smaller, and the changing position is performed in a case where the magnitude of the force detected by the external force detection unit is larger than the predetermined threshold.