Designing a Single-Leg Robotic Exoskeleton for Hemiparesis Patient Gait Assistance
Noah Garcia
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07/26/2021
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The purpose of this study was to design a single-leg robotic exoskeleton for hemiparesis stroke patients in order to assist disabled individuals in performing natural gait patterns. Although there are many existing exoskeleton designs for augmenting human strength and other useful functions, this study’s design uniquely focuses on correcting hemiparesis patients’ gait while providing additional torques that help the patient propel forward and extend their leg, achieving a full range of motion.
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- [00:00:02.130]Hello.
- [00:00:02.963]My name is Noah Garcia.
- [00:00:04.210]I'm a Junior Mechanical Engineering Major
- [00:00:06.320]at the University of Nebraska.
- [00:00:08.810]This summer, I did research with Dr. Carl Nelson
- [00:00:11.440]on designing a single-leg robotic exoskeleton
- [00:00:14.180]for hemiparesis patient gait assistance.
- [00:00:17.310]So let's go through some of the background.
- [00:00:20.020]Hemiparesis is a partial loss of muscular strength
- [00:00:23.070]on one side of the body.
- [00:00:24.960]It's most commonly brought upon by strokes.
- [00:00:27.960]Mild to moderate cases create asymmetrical gait
- [00:00:31.270]leading to further long-term injury and disability.
- [00:00:34.780]So currently, patients with hemiparesis
- [00:00:38.870]use a couple of manual assistive devices, walkers and canes.
- [00:00:42.990]However, these two devices carry serious drawbacks.
- [00:00:46.290]Walkers are considered a little bit too bulky and heavy
- [00:00:50.070]and canes increase the risk of falling.
- [00:00:52.730]Most notably, however,
- [00:00:54.420]leaning on these assistive devices during gait
- [00:00:57.520]exacerbates asymmetrical walking patterns.
- [00:01:02.290]So one alternative to these manual assistive devices
- [00:01:06.900]is rigid exoskeletons.
- [00:01:09.620]You could see one on the right on figure 1.
- [00:01:13.160]They're made of metals and plastics.
- [00:01:15.340]Of course, rigid materials.
- [00:01:17.540]They're bulky and high inertia.
- [00:01:19.820]They usually produce high torques
- [00:01:21.630]to replicate movements of the body.
- [00:01:24.570]They're used for patients with severe paralysis
- [00:01:27.530]who often can't walk or even stand on their own.
- [00:01:33.500]And they're very costly and usually only available
- [00:01:36.980]to rehabilitation centers, not private use.
- [00:01:41.020]So another alternative is the development of soft exosuits.
- [00:01:46.320]So these soft exosuits,
- [00:01:48.190]you could see one to the left on figure 1,
- [00:01:51.070]they're made of textiles,
- [00:01:54.190]flexible materials.
- [00:01:55.840]They are low inertia and they produce lower torques
- [00:01:58.560]than rigid exoskeletons.
- [00:02:00.370]However, they're used for augmenting strength
- [00:02:04.010]of healthy humans, not assisting disabled individuals
- [00:02:09.240]with
- [00:02:11.720]their gait patterns.
- [00:02:13.840]Which brings us to our purpose.
- [00:02:16.490]The purpose of the research is to design
- [00:02:18.640]a single-leg robotic exoskeleton
- [00:02:20.670]to assist hemiparesis patients
- [00:02:22.420]in the performance of gait cycles.
- [00:02:26.100]So let's go through some of our materials and methods.
- [00:02:29.670]First, of course, we had to gather information.
- [00:02:32.070]We compiled information regarding existing exoskeleton,
- [00:02:35.570]exosuit and actuation technologies and put them together
- [00:02:40.900]according to our specific design and specific population.
- [00:02:47.050]These sources included patents and research articles.
- [00:02:52.210]Next, we moved on to concept generation.
- [00:02:55.530]We used SolidWorks software to model the design in 3D.
- [00:03:01.360]And we completed calculations to select the optimal mode
- [00:03:05.710]of actuation according to our torque and power parameters.
- [00:03:11.470]So let's go through some of our results.
- [00:03:14.450]Here on the left, you could see our
- [00:03:17.750]3D models on SolidWorks.
- [00:03:20.440]Here on the left, upper left,
- [00:03:23.780]you could see the isometric view of the device.
- [00:03:27.050]This shows each component a little bit more clearly.
- [00:03:30.950]You could see each shade is a different material.
- [00:03:34.800]So,
- [00:03:36.540]and then on the upper right,
- [00:03:38.840]you could see a close-up of the motor
- [00:03:41.750]or actuation assemblies that apply,
- [00:03:44.690]and applying torques on the thigh and shank.
- [00:03:46.890]So let's go through some of the explanations here.
- [00:03:49.880]So our motive actuation is a
- [00:03:51.430]DC brushless planetary gear motor.
- [00:03:54.260]These types of motors produce really high torque.
- [00:03:57.110]They're a little bit smaller
- [00:03:58.450]and they're very easy to acquire.
- [00:04:00.380]You could just go to online and order them.
- [00:04:04.660]Next, we have the ways in which they work.
- [00:04:07.980]Force displacement.
- [00:04:09.010]How do we produce those forces
- [00:04:10.490]and displace them along the device?
- [00:04:12.840]So tensile forces are created by a cable
- [00:04:15.730]attached to a rotating motor,
- [00:04:17.490]as you could see in figure 3.
- [00:04:20.280]And it's, the action is similar to the retraction nature
- [00:04:23.780]of a line on a fishing reel.
- [00:04:26.120]You could see that a little bit more clearly in figure 4.
- [00:04:32.120]Force is displaced by cables in tension so that these,
- [00:04:36.322]these forces are transmitted through these cables.
- [00:04:41.380]Of course, these cables are going to provide a net force up
- [00:04:46.180]because they are pulling up on those pulleys.
- [00:04:48.990]So we need to find a way to counteract those net forces
- [00:04:52.750]in order to prevent the device riding up the leg.
- [00:04:56.740]We don't want the device riding up the leg.
- [00:04:59.020]Of course, we want the device to stay put
- [00:05:01.650]relative to each component
- [00:05:03.300]and relative to where we want them to be on the leg.
- [00:05:07.000]We don't want any pieces moving around.
- [00:05:09.190]We want them to stay put.
- [00:05:10.300]So this is why we connected the entire device together
- [00:05:15.620]in one piece, so that none of the,
- [00:05:18.710]none of the individual components move
- [00:05:20.890]relative to each other.
- [00:05:22.900]Next, we have the torque distribution.
- [00:05:24.740]How do we apply and distribute torques to turn that leg?
- [00:05:28.920]Well, a torque is created using tension
- [00:05:31.340]along a non-slip pulley.
- [00:05:33.740]Two pulleys are located at the thigh
- [00:05:35.760]and shank centers of mass.
- [00:05:37.040]You could see them, of course, pretty clearly
- [00:05:39.730]connected to those white components right there.
- [00:05:44.490]These pulleys will turn
- [00:05:48.740]from the cables pulling on them and the rigid components,
- [00:05:52.420]that white component that you see on the thigh and shank,
- [00:05:56.310]they will turn with them.
- [00:05:58.420]Their torque is more evenly distributed
- [00:06:01.330]using these rigid components.
- [00:06:04.480]We don't want the pressures to be too high to,
- [00:06:09.140]this ends up causing
- [00:06:11.510]really
- [00:06:14.150]bad discomfort in our, in our patients.
- [00:06:17.770]Using a rigid component
- [00:06:20.970]that distributes these,
- [00:06:23.070]these torques better then you could have
- [00:06:24.960]a little bit more comfort with the patient.
- [00:06:28.920]Next, we have energy absorption and release.
- [00:06:31.980]Compression and tension forces are absorbed and released
- [00:06:34.840]using elastic material.
- [00:06:36.540]You could see the elastic material, it's denoted in black.
- [00:06:40.510]These are the black components right on the knee
- [00:06:42.700]and the ankle.
- [00:06:44.070]These two elastic bands are attached,
- [00:06:45.790]of course at the knee and the ankle,
- [00:06:47.310]to assist in knee extension and dorsiflexion respectively.
- [00:06:54.000]We use these elastic components
- [00:06:55.680]to reduce the amount of force that we need to exert
- [00:06:59.750]from the actuation units.
- [00:07:02.620]As long as we could absorb that material
- [00:07:04.660]and naturally release it using that extension,
- [00:07:07.290]that these elastic bands,
- [00:07:10.700]then we reduce the amount of force that we need to input.
- [00:07:15.100]Next, we have some future research.
- [00:07:17.990]So future research is optimizing the design mechanics,
- [00:07:22.770]introducing design components for user comfort,
- [00:07:25.780]such as cushions or maybe
- [00:07:29.420]some extra elastic components that help you
- [00:07:32.960]be more comfortable walking.
- [00:07:34.880]We have to select materials for each component
- [00:07:38.180]and prototype the separate components.
- [00:07:40.870]And I'd like to acknowledge Dr. Carl Nelson,
- [00:07:43.990]who is my research mentor and the McNair Scholars Program.
- [00:07:48.210]Thank you very much for listening.
- [00:07:50.340]This is the poster
- [00:07:53.290]as a whole, as you saw in the beginning of the presentation.
- [00:07:56.510]Thank you.
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