Method and apparatus for measuring physical displacement

A displacement sensor assembly comprising:

• a first cantilever beam;
• a second cantilever beam;
• a first strain sensor;
• a second strain sensor;
• a third strain sensor;
• and
• a temperature sensor;
• wherein the first cantilever beam is physically oriented such that the longitudinal axis of the first cantilever beam is perpendicular to the direction of displacement about a first detection axis and parallel to the direction of displacement about a second detection axis;
• wherein the second cantilever beam is physically oriented such that the longitudinal axis of the second cantilever beam is perpendicular to the direction of displacement about a third detection axis;
• wherein a first end of the first cantilever beam is fixably mounted to a fixed reference and a first end of the second cantilever is fixably mounted to a moving reference;
• wherein a second end of the first cantilever beam is joined to a second end of the second cantilever beam;
• wherein the first strain sensor is mounted and calibrated to detect displacement between the fixed and moving reference by measuring strain on the second end of the first cantilever beam about the first axis of detection and the second strain sensor is mounted and calibrated to detect displacement between the fixed and moving reference by measuring strain on the second end of the first cantilever beam about the second axis of detection;
• and the third strain sensor is mounted and calibrated to detect displacement between the fixed and moving reference by measuring strain on the second end of the second cantilever beam about the third axis of detection;
• and,
• wherein the temperature sensor is mounted and calibrated to counteract the effect of thermal strain on the sensor assembly.

A method of measuring displacement between two surfaces comprising the steps of:

• a. Providing a displacement sensor assembly comprising;
• i. a cantilever beam;
• ii. a reaction block;
• iii. a strain sensor;
• and
• iv. a temperature sensor;
• wherein the cantilever beam is physically oriented such that the longitudinal axis of the cantilever beam is perpendicular to the direction of displacement;
• wherein a first end of the cantilever beam is fixably mounted to a fixed reference and a first end of the reaction block is fixably mounted to a moving reference;
• wherein a second end of the cantilever beam is joined to a second end of the reaction block;
• wherein the strain sensor is mounted and calibrated to detect displacement between the fixed and moving reference by measuring strain on the second end of the cantilever beam;
• and
• wherein the temperature sensor is mounted and calibrated to counteract the effect of thermal strain on the sensor assembly;
• b. calibrating the strain sensor to detect displacement of the second end of the cantilever beam;
• c. calibrating the temperature sensor to detect the temperature of the sensor assembly;
• d. calculating the amount and direction of displacement according to the output of the strain sensor;
• e. adjusting the calculated amount and direction of displacement to account for temperature coefficient of expansion effects in the cantilever beam.