Here’s a video of me testing the hip actuation while walking with the walker:

This is a video from the testing I mentioned in my previous post. The thoughts for improvement from that post still apply.

The main thing that I’m focusing on right now is improving the rigidity, positioning, and torque of the hip motor through a more structured attachment to the upper body. As I mentioned in the last post, I’m leaning toward a rigid frame that extends from the shoulders down to the lower back and attaches to the leg portion of the device. Sort of like an external frame backpack. Having that more stable structure will then allow for moving on to affixing the knee motor and a foot support/spring actuator w/o worrying as much about the weight of those features.

For the back frame, I’ve been exploring using PVC tubing or 80/20 stock for mocking up the structure in order to iterate quickly through different dimensions and configurations.

Exo controller circuit cleaned up in new project box with new FSR trigger on walker handle

I’ve finished cleaning up the exo controller circuit, moving it from the breadboard to an Arduino proto shield. It also lives in a new project box (as seen above, positioned on top of the walker). The gray mini-din cable coming out of the side of the box through a mini-din panel mount port connects to the hip joint servo motor for communication.

To the right in the picture above is a new force sensitive resistor (the tab leads on the previous one wore off).

Here’s a broader shot of the walker and exo brace together:

Walker with exo controller in new enclosure

The goal of transferring the exo circuit away from the breadboard was to be able to test more thoroughly which I did do last night. I have some more video of the testing that I’m hoping to get up on YouTube and here soon. In getting the chance to test the device while walking last night, a few  thoughts struck me that I plan to further explore:

  • It seems that the actuation of the hip joint could be smoother and more effective by altering the design a bit. When the actuation occurs, there seems to be resistance as the knee rises. This is natural of course because of gravity but it seems that the device and the leg buckle also causing increased resistance. As the hip joint angle changes so does the distance from the top of the upper leg segment of the brace to the location of the leg. In other words, adding some sort of flexibility to the piece of the brace that straps to the upper leg might make the actuation more effective. One thought is putting the connection on a slider (i.e. a desk drawer sliding mechanism) so as the angle changes the upper leg could still be pulled up but where exactly the brace segment is attached to the thigh could change
  • The current thigh portion of the brace is somewhat of a longer segment that spans upwards of a foot along the thigh with two straps and rigid plastic behind this segment. In thinking about the above problem, it may be that this segment could be designed better perhaps so there is a strap further down right above the knee and another strap further up the thigh and not the larger plastic segment connecting the two.
  • The idea of incorporating should straps to the device as well as maybe a rigid back section keeps popping into my mind. Doing so would definitely offload some of the weight of the brace more effectively. As the device is worn right now the weight of it definitely adds strain over time which would be even more of any issue for users that are already weak in the lower body. Adding the back support would also add rigidity to the hip joint actuation and may in turn increase efficiency.
  • Knee joint articulation is necessary at this point. I’d like to try a purely mechanical approach to this harnessing the power of the hip joint servo as a way to keep the cost and weight down. We’ll see how well that turns out

I’ve added a force sensitive resistor to use a force sensor to the heel of a shoe to detect when the user’s body weight is shifted forward off the heel. During human gait, the rear heel of the rear leg that is about to swing forward comes up first. In the case of my Mom, she has the ability to pull her heel up on her right leg (her weak leg) and so now we can sense this w/ the FSR and trigger the stepping pattern in the exoskeleton knee and hip flexor joints with the linear actuators. If steady pressure is sensed by the FSR connected to the microcontroller (using Arduino) then the sequence will not engage.

Here is a video of me testing the heel sensor.

I’m thinking too that it might be good to add an additional check sensor. Perhaps another FSR to read hand squeeze on the walker or an actual trigger button. This might be necessary because if the user doesn’t wish to initiate that walking step but shifts her body weight while engaged in the suit a certain way the FSR reading could improperly signal a walking step. Another thought I had is to determine the position of the left foot relative to the right foot. Because if we know that, we know that if the left foot is in front of the right then that’s another enforcing reading that a full step is desired with the right leg. Whereas if we know that the left foot is next to or behind the right, a full step most likely wouldn’t be desired. It’s reasonable to conclude that the right step wouldn’t be desired in the side-by-side scenario in my Mom’s case is again because the left side is the stronger side and so therefore would be the leading side.

© 2011 OpenExo Suffusion theme by Sayontan Sinha