Haptic knob leverages magnetorheological fluids for crisp force-feedback

Haptic knob leverages magnetorheological fluids for crisp force-feedback
Technology News |
Developed by List, a research institute of CEA Tech focused on smart digital systems, the MATISS (Magneto-Textural Inertial Spinning System) is a novel type of rotary knob that integrates a highly programmable passive brake together with a small electric motor to allow for many types of haptic effects including force-feedback, elastic force and coil rebound.
By eeNews Europe


In particular, the passive brake consists of a magnetorheological fluid flowing between intertwined bell-shaped walls, whose viscosity can be tuned arbitrarily by controlling its phase transition from liquid to solid (and vice versa) by a magnetic field (from a built-in coil). While the liquid phase offers no resistance to the knob’s rotation, the solid phase ensures a solid stop.

The prototype originated as follow up work from prof. Carlos Rossa’s thesis “A hybrid actuation system for haptic interfaces”, which already hinted at the device’s construction with fluid gaps arranged between dome-shaped enclosures.

Interviewed by eeNews Europe, Moustapha Hafez, head of the Sensory and Ambient Interfaces Laboratory at CEA List gave us more technical details about the device.

“Because we can control the passive brake electronically, we can create virtual hard stops, to simulate a collision or provide progressive resistance, and anything in between. Due to the very nature of the magnetorheological fluid we use, there is hardly any friction in the off-state, something in the range of 2mN/m. But if we apply 1.5A to the coil, the magnetic field turns the fluid solid and this locks the knob with a force of 2N/m. That’s three orders of magnitude between the “on” and “off” force couples” Hafez explained.

But how fast is the knob’s response time? We asked.

“The phase transition occurs in milliseconds, and in this implementation, the coil’s inductance and the time it takes to create the magnetic field is the limiting factor, between 5 and 10ms. That still means we can create very fast and closely-spaced clicking sensations, at frequencies in the 100Hz range. The frequency spectrum we can perceive as humans ranges from a few Hertz to hundreds of Hertz, with a peak of sensitivity at 250Hz. Hence we have plenty of room to emulate vibrations and even textures just by controlling the passive brake” the researcher told eeNews Europe.

“In our CES demo, opening a safe, we coupled the haptic effects with audio rendering of the clicks. By fusing the two and stimulating two sensory modalities, we really augmented the overall haptic rendering”.

“What’s more, the knob also integrates a motor, which, combined with the passive brake, can be used as a reverse force input to create an elastic torque, or a spring effect imparting a notched sensation to the clicks. The motor can also be driven to create static vibrations, or to reset the knob to its initial position or on the contrary you could create inertial effects with the knob still turning as you release it” Hafez continued.

Next, the idea is to develop a library of haptic effects through that proprietary haptic interface, whose parameters customer could modify to customize these effects or program different stop and click patterns, even perceivable textures. 

How about joysticks then?

“The real novelty was that we were able to tightly encapsulate the magnetorheological fluid between multiple imbricated bell-shaped walls, an innovative passive brake architecture that yields very strong braking forces. The rotating knob is a one-axis implementation, but we are also developing 2-axis joysticks constructed with one module per degree of freedom, mechanically enclosed one in another”, Hafez said. “Control sensitivity can be tuned through the signal amplification chain. So with the same basic modules, we can make a high accuracy joystick that a surgeon would control with three fingers to operate a surgical system, or we could create heavy machinery and gaming joysticks with real hard stops and a more reactive force”.

“We are currently developing such joysticks for a partner we cannot disclose at the moment, but this may be another demonstration at CES 2019”, the scientist concluded.

In addition to gaming and the applications demonstrated at CES, applications for MATTIS technology range from transportation to construction to manufacturing. Some potential applications include driving or operating assistance for cars, buses, trucks, agricultural vehicles, construction machinery, planes, helicopters and submarines. Such haptic joysticks could be used to better control drones, allowing the operator to feel the effects of wind and proximity to obstacles, but also for a variety of remotely controlled robots.

List – www-list.cea.fr

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