A comparison of force sensing for applications in prosthetic haptic feedback

The current study presents a comparison of two load sensor designs that can be applied toward haptic feedback sensing in upper limb prosthetics. A lab-standard capacitive load cell sensor is discussed, which is succeeded by the proposal of an electrochemical sensor. Experiments were conducted primarily as a proof-of-principle study to evaluate sensor characteristics for prosthetic applications. The aim is to address the need for minimally invasive, cost-effective prosthetic sensor technologies, as the investigated sensor designs conceptualize applications of average grip forces. Thus, force requirements for the sensors were determined to be 250–500 N per the average maximum grip strength of healthy adults. Comparable to a commercial gold-standard capacitive load cell design, a lab-standard load cell sensor was inexpensively manufactured using conductive foam. The lab-standard design was improved upon by employing electrochemical techniques and CP-9000, a thermoplastic elastomer material, to form an electrochemical sensor for enhanced sensitivity. Sustained loads ranging from 0.49 to 2.45 N resulted in average maximum current readouts of − 1.25 × 10⁻¹ to − 4.25 × 10⁻¹ for the lab-standard sensor, and − 5.95 μA to − 7.85 μA for the electrochemical sensor. The electrochemical sensor was reproducible and demonstrated the potential to discriminate between various loads. Force requirements were not reached; however, future studies will seek to increase the mechanical strength of the electrochemical sensor. As the initial electrochemical sensor design provides a potential method for low-cost computer-based prosthetics, thermoplastic elastomer materials with increased elastic and mechanical strength properties will be investigated.