Servo-control system

A system, comprising:

• an actuator comprising a movable member configured to provide a load to transfer a substrate between a support and a transfer plane;
• a proportional valve configured to control fluid flow between the actuator and a pressurized fluid supply or a vent;
• a pressure sensor configured to measure pressure in a supply line to the actuator;
• a position sensor configured to measure a position of the movable member;
• and
• a controller to:
• determine an output force based on a commanded force and an estimated force, wherein the commanded force is based at least in part on a position measurement of the position sensor, and wherein the estimated force is based at least in part on a pressure measurement of the pressure sensor and the position measurement;
• generate a control signal based on the output force;
• and
• apply the control signal to a proportional pneumatic valve to move the movable member to a target position.

A method, comprising:

• actuating a proportional valve to permit fluid to flow through a first fluid line into a first chamber of an actuator and through a second fluid line into a second chamber of the actuator;
• measuring pressure in the first fluid line with a first pressure sensor and measuring pressure in the second fluid line with a second pressure sensor;
• measuring position of a movable member of the actuator with a position sensor, wherein the movable member is configured to provide a load to transfer a substrate between a support and a transfer plane;
• determining an output force based on a commanded force and an estimated force, wherein the commanded force is based at least in part on the position of the movable member, and wherein the estimated force is based on the pressure in the first fluid line, the pressure in the second fluid line, and the position of the movable member;
• and
• controlling the proportional valve to apply a contact force of about 2 N to about 10 N by the movable member based on the output force.