Magnetoresistive force sensors for use in an instrumented pen

Abstract

Abstract The project involves the design of a magnetoresistive force sensor to provide a feedback element in an instrumented pen. The pen, together with a functional electrical stimulation system, would allow writing to be achieved by tetraplegic patients. Experiments have been carried out to define the force range and force sensor design required for successful writing. Considering that tangential and normal forces are to be measured, magnetoresistive sensors are selected as the transduction technique. Experiments with current-carrying conductors and permanent magnets have been carried out to define the magnetic source for the sensors, in an attempt to optimize the system for low power consumption. Cast and sintered alloy magnets are finally chosen. If this type of permanent magnet is put in an orthogonal position with respect to the sense element plane, a lateral displacement sensitivity of −40 mV/mm in a range of 1.5 mm can be achieved, with low sensitivity to the separation between the magnet and the sensor (−5 mV/mm).