Force sensors operate on the principle that the resistance of silicon-implanted piezoresistors will increase when the resistors flex under any applied force. In this, the force measurement is based on the determination of a displacement subject loading. The strain gauges have been used primilarly to analyze forces, but lately piezoelectric transducers are used for the measurement of forces. In tumbling mills, the forces on the lifter bars are quite sensitive to impact and collision. The instrumented lifters incorporating force sensors are used to monitor the performance of tumbling mills. The amount of resistance changes in proportion to the amount of force being applied. This change in circuit resistance results in a corresponding mV output level. These sensors are normally used to measure the robotic system's forces as it performs various operations.