The implementation of the project consists of two main sections, the hardware and the software.
As for hardware, two generations of the exoskeleton have been developed and tested for structural functionality.
Inspired by designs availbe in academia and markets, the team firstly designed the mechanical structure in Solidoworks, a CAD software commonly used for mechanical design.
The first generation looks similar as below:
Figure 2. Front view of the First Generation
Figure 3. SIde view of the First Generation
Figure 5. Design View of first Gen in Solidworks Figure 4. Testing first Gen with passive actuator
The first generation was designed in CAD software Solidworks before actual assembly. With skills obtained in our past experiences in the HKUST Robotics Team and Robomaster Team, we carefully designed the first generation exoskeleton. The design focused on structural strength and low cost. So the components were chosen to be industrial grade standards and sizes.
After designing the basic structures and finished checking for potential errors, the main components design files were sent to the manufacturers. several components were made in house and key conponents such as the motors were purchased.
The first generation structure was assembled early in October and several tests to check the structural functionality were conducted on the frame. A temporary passive actuator made with high tension rubber bands were installed and served as a source of assistance. A screenshot from one of the test videos can be found on the previous page:
Several issues were identified with the first generation design, apart from being too rigid and limited in degrees of freedom, the biggest issue was the weight of the system. Initially aiming for support forces of up to 80kgf, the frame was designed to hold at least a 100kg of loading, this resulted in a very heavy system within which the frame itself weighs over 20kg and the total estimated weight will be around 30kg. This weight is slightly above applicable, we decided to design a lighter second generation exoskeleton with a little compensation for maximum support force.
Later, a second version was designed with similar methods, apart from changing to a lighter and more portable design, the team also modified the harness system from a medical retainer to realize more comfort in wearing the exoskeleton. Slight structural changes, such as modifying the structure near the shoulder area to resolve conflicts with the user, were also made to the second generation based on trial and error method to further improve comfort.
Pictures of the second generation can be found below:
Figure 6. Front view of Second Generation frame Figure 7. Side View of Second Generation frame
After finishing the frame of the second generation and tuning the harness to an optimal setting. The team started developing the driver module of the exoskeleton. The driver module was initially designed to be using two motors and drive one single tendon to provide support for the user, however it was later decided that the two motors will be used seperatly to provide support for each leg. This is because the original design might be having efficiency issues at certain poses and the physical connection between the two legs also limits the user’s movement.
For software, development and testing have been conducted on multiple subsystems of the project, the team have tested functionality of every separate sensor and written driver programmes to acquire data and control the motor outputs.
Later, after the mechanical and hardware systems were finished, the team combined the separate software components and added a simple assistance strategy to assist when the user swings his/her leg backward while moving forward or upward.
Figure 8. Design view of the initial driver module
Figure 9. Finished Updated Driver Module
The finished exoskeleton, together with its key features, can be found as the picture below:
Figure 10. Finished Exoskeketon and Key Features
SECTION 3—RESULTS 3.1 Testing
The project originally planned to conduct field testings with students and workers to acquire data, however due to the virus outbreak the testing procedure will have to be changed. The team is currently actively looking for alternative test methods that require less interactions. The currentl plans includes reducing number of test pilots and reducing test sets.
As the quantitive measure for back stress is harder to acquire, the team have changed the goal of the project to reducing metabolic cost for users during climbing activities, this way the tests will be easier to quantify and results will be more convincing. However as HKUST currently does not have the measuring device, those tests might have to be outsourced. Possibly to SUST in Shenzhen after the virus outbreak is under control.
If such tests cannot be carried out before the projects ends, an alternative method is just to send questionaires for participants and record their responses, this evidence will be weaker in credibility but it still proves the effect of the exoskeleton.
The team have already performed several functional (such as stair climbing and weight lifting) tests with the finished exoskeleton, a picture of which can be found below:
3.2 Evaluation
Currently the project have reached a really important milestone, which is building and testing the first functional prototype.
The tasks for the team include further improving the control algorithm and assistance strategy in the future to achieve better performance in terms of more natural transition between operation modes and more accurate gait pattern detection.
Further testing involving quantitative measure of muscle activity (EMG) and metabolic cost (CO2 consumption) have not yet been conducted due to equipment limitations, but those are planned to be carried out in the future. Either in HKUST or in SUST.
3.3 Competitiveness Advantage
The project exhibits several rather distinct features versus other projects in the market, which includes:
1) Light-Weight: the prototype has less than 14 kg with battery, which makes the product less tiring to wear.
2) Cost Efficient: prototype costs below HKD 6,000, which is lower than some of the existing exoskeleton devices with similar functions.
3) Powerful: the estimated assistive torque is over 64Nm for each leg.
4) Safe: the project has included multiple levels of safety considerations, due the fact that target audience might include workers or elderlies. Safety would be among their top priorities in selecting such products.
5) User Friendly: the protype is comfortable to wear and operate.
3.4 Looking Ahead
This project plans to go beyond simple prototypes. The team holds the vision that this project continues to improve and ultimately reach industry grade to be manufactured and made commercially available for those in need.
The cost-efficient nature of the design means that the final product cost will have a significant drop on top of the already low prototype cost, resulting in much better accessibility for the general public.
The platform is also designed as an opensource project with mostly standard components, which will enable other research groups to build and use it as a benchmark platform on which to conduct research and development.
The team also intends to seek collaborations to further conduct research and look for monetization opportunities. Potential collaborators include relevant projects and labs from universities such as HKUST, Southern University of Science and Technology, ETH Zurich, as well as companies such as Xeno Dynamics etc.
Overall, the project is expected to impact greatly both on the general public and the industry.
3.5 Total Budget(Estimate)
Parts tested but not selected $5000
Total ~$14200
REFERENCES
[1] Matthias B, et al. (2018). Passive Back Support Exoskeleton Improves Range of Motion Using Flexible Beams. Frontiers in Robotics and AI, Vol. 5, No.72. DOI: 10.3389/frobt.2018.00072
[2] Stefano, Toxiri. (2019). Back-Support Exoskeletons for Occupational Use: An Overview of Technological Advances and Trends. IISE Transactions on Occupational Ergonomics and Human Factors, 0, 1-13. DOI:
10.1080/24725838.2019.1626303
[3] Ting, He. (2018.) A Lower-Back Robotic Exoskeleton. IEEE Robotics and Automation Magazine, 0, 95-107.
DOI: 10.1109/MRA.2018.2815083
[4] H-Wex by Hyundai: (https://exoskeletonreport.com/product/h-wex/) [5] Back-X by Suit-X: (https://www.suitx.com/backx?)
[6] HAL by Cyberdyne: (https://www.cyberdyne.jp/english/products/Lumbar_LaborSupport.html)