Thin, flexible force sensors have appeared as an alternative for many force measurement applications where traditional sensors are not appropriate. These sensors fit easily over curved surfaces, are extremely light weight and are available in a wide variety of formats. For measurement of grip force, sensing elements can be placed on a glove, directly onto a hand, or onto a handle or grip surface. They, therefore, overcome limitations of sensors such as load cells which need to be incorporated into the handle design resulting in poor spatial resolution and affecting the properties of the object being gripped. Although there are clear benefits to using thin-film force sensors for certain applications, sensor performance and reliability have not been sufficiently evaluated.

Aim

The aim of this study was to examine three different thin-film force sensors under both controlled laboratory conditions and in a real gripping situation to give an indication of each sensor’s static accuracy, hysteresis, repeatability and drift errors, dynamic accuracy and drift errors, and the effects of shear loads and surface curvature.

Approach

  • Three types of thin, flexible force sensors were investigated: QTC, Tekscan 9811 and Flexiforce sensors.
  • All sensors were calibrated according to the manufacturer’s guidelines
  • The sensors were subjected to a rigorous and comprehensive set of static and dynamic tests to determine their characteristics under varied loading conditions.
  • Novel tests were developed to evaluate shear force sensitivity and dynamic sensor behaviour under sinusoidal loading up to 100 Hz.

Key Findings

  • Tekscan 9811 and Flexiforce sensors had static errors that were not negligible (3-10%) but were acceptable given the advantages they offered over alternatives for the grip force application.
  • Tekscan 9811 had a larger drift error than the Flexiforce sensor.
  • For dynamic loads, the sensitivities of both Tekscan 9811 and Flexiforce sensors were both measurably reduced compared with the sensitivity found using quasi-static loads.
  • QTC sensors displayed quite large drift and curved surface errors and in these tests did not perform as well as the Tekscan sensors.

Publications