Six-axis force and torque sensors measure the full six components of force and torque: vertical, lateral, and longitudinal forces as well as camber, steer, and torque movements. Six-axis force and torque sensors provide electrical outputs as analog current loops, analog voltage levels, frequencies, pulses, switches and relays. Typically, analog current loops are 0 – 20 mA or 4 – 20 mA. Most analog voltage outputs are 0 – 10 V or ± 5 V. Frequency and pulse signals include amplitude modulation (AM), frequency modulation (FM), and pulse width modulation (PWM). With switch or relay outputs, contacts are open or closed depending on the state of the variable being monitored. Typically, six-axis force and torque sensors are used in strain gauges, piezoelectric devices and optical instruments. They are also used to monitor robotic hand movements and the performance of car and truck tires.
General specifications for six-axis force and torque sensors include sensor height, sensor weight, and sensing technology. Typically, sensor height is measured in inches and sensor weight is measured in pounds. With six-axis force and torque sensors, there are three basic types of sensing technologies: strain gauge, piezoelectric, and optic. With strain gauge devices, strain-sensitive variable resistors are bonded to part of the structure, which deforms when measurements are taken. Typically, strain gauges are used as measurement elements in Wheatstone bridge circuits. With piezoelectric devices, compressing a piezoelectric material generates a charge that is measured by a charge amplifier. Optical devices use photodiodes or other fiber optic technologies to detect optical power and convert it to electrical power.
Selecting Six-Axis Force and Torque Sensors
Selecting six-axis force and torque sensors requires an analysis of force and torque requirements. There are three measurement ranges for force. X-axis force is a longitudinal measurement range, Y-axis force is a vertical measurement range, and Z-axis force is a lateral measurement range. There are also three measurement ranges for torque. X-axis torque is measured around the longitudinal axis, Y-axis force is measured around the vertical axis, and Z-axis force is measured around the lateral axis. Additional considerations include force measurement accuracy, torque measurement accuracy, operating temperature, shock rating, and vibration rating. Typically, force and torque accuracy measurements are expressed as a percentage with six-axis force and torque sensors. Shock and vibration ratings are usually maximum amounts.