Linear Resonant Actuator tests

A project log for Digital White Cane

The Digital White Cane can prevent frequent head injuries and provide intuitive navigation assistance for the blind and visually impaired.

George AlbercookGeorge Albercook 10/21/2017 at 01:250 Comments

They definitely start and stop quickly and it seems that you can get a more varied output but there is still a problem. It took awhile to figure out how to even explain it.  They the actuators we're on the table it was clear that the amplitude was changing with the distance to objects and when you touched the actuators you could feel the difference but when you put the device on your head they felt less lively for lack of a better term. It looks like there are two things going on here. Apparently, the driver chip has a calibration mode which we have not used yet. The documentation says they will not work comparably and properly until they are calibrated. 

But we expect that there is another issue.  We noticed that when you reach out to touch an actuator if you press too hard you stop it from moving very much and if you touch too lightly you can't feel it move.  People appear to automatically adjust their touch pressure to maximize the movement of the actuator. Everyone seems to do it and they do it almost instantly. 

Unfortunately, when the devices are strapped to your head there is no self-adjusting. We tried mounting them on foam, in foam Wells so they could move freely, stuck to the headband or stick to your head. Many of these methods worked well enough but compared to the auto-calibration that people do with their fingers they are not performing as well as they could.

So our next idea is to mount each LRA on a plastic strip and adjust the length and width be of the strip until it resonates at the same frequency as the LRA. That is about 240Hz. This will give us a reproducibly secure mounting method that interferes with the actuator as little as possible. Then we can adjust how hard the actuator rests against the forehead and try different touching surfaces and shapes. Maybe a cone-shaped piece of foam that only touches at the point at low amplitude and touches a larger area at high amplitude. We will have to test and see.

Either way ERM or LRA the system works we are just optimizing now.