Robots with adaptive grip enabled by optical force sensors

OptoForce, a Hungary-based start-up, has developed an innovative touch sensor that brings adaptive grip to robots. The optical force sensors have yet to appear to market, but the company has already brought the technology to academic institutions to enable a number of applications.

Spun out from Budapest's Pazmany Peter University in 2013, the company was initially founded while doing research on walking robots, explained Akos Domotor, the company's CEO.

Two of my colleagues were doing a PhD with a special focus on sensing robot gait, trying to measure leg inertia and detect foot slip with largely varying forces. We came up with a first prototype in 2012, and after thousands of iterations, we were able to optimise our sensors into their actual dome shape with a very linear output, Domotor said.

The optical force sensors have a very simple construction, consisting of a silicone dome covering a central LED and four light sensing elements measuring the light reflected by the dome. By construction, any deformation of the dome along its X, Y or Z axis (through external pressure) will yield a different set of values across the photodiodes.

After a thorough calibration of the sensor, these values can be translated into precise forces values, giving not only force magnitude but its direction, so a simple joystick could be designed out of a single sensor. The company also designed a 6-axis force/torque sensing unit based on an array of such sensors. Correlating the force direction across all sensors gives the overall torque.

The sensors can be designed with various dome sizes of different thickness or made up of different silicone materials (of varying hardness) depending on the final application requirements, say for harsh environments, but the algorithm running to interpret the data is the same as long as calibration has been performed. So in essence, because the electronics is protected by the deformable dome, they are very rugged.

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