Robot with force control

A robot comprising:

• a base;
• a support extending from the base;
• an arm assembly operatively coupled to the support and moveable relative to the support, the arm assembly comprising a first arm link arranged to rotate relative to the base about a first rotary axis and a second arm link coupled to the first arm link and arranged to rotate relative to the first arm link about a second rotary axis;
• an arm assembly drive arranged to move the arm assembly relative to the support, the arm assembly drive including an arm assembly motor and drive train arranged to move the arm assembly and having a drive ratio of 25:1 or less;
• a first arm link drive including a first motor and drive train arranged to rotate the first arm link relative to the base about the first rotary axis and having a drive ratio of 25:1 or less;
• a second arm link drive including a second motor and drive train arranged to rotate the second arm link relative to the first arm link about the second rotary axis and having a drive ratio of 25:1 or less;
• an end effector coupled to the arm assembly and configured to hold an elongated object;
• and
• a controller constructed and arranged to provide control signals to the arm assembly drive and the first and second arm link drives to move the end effector relative to the base, the controller constructed and arranged to determine external forces and torques in Cartesian coordinates acting on the end effector or on an elongated object held by the end effector based on a torque increase or other change for the first and second motors of the first and second arm link drives and without use of force sensor information;
• wherein the controller is configured to control the robot to move an elongated object held by the end effector with respect to a storage area in a placement direction to position the elongated object at the storage area such that the robot rotates or permits rotation of the elongated object about one or more Cartesian axes transverse to the placement direction and continues to move the elongated object in the placement direction in response to an external force on the elongated object having a component in the placement direction that is above a threshold, such rotation and movement along the placement direction allowing the elongated object to move in the placement direction while maintaining the component of the external force in the placement direction on the elongated object to be below the threshold.