Assistive Exoskeleton
for Workers and Elders
HKUST President’s Cup Technical Report
Project Name: Assistive Exoskeleton for Workers and Elders
Supervisor:
Professor Ling Shi, Dept ECE, HKUST
Author:
ZHANG YU
Student ID:
TABLE OF CONTENTS
SECTION 1—INTRODUCTION... 1
1.1 Background ... 1 1.2 Objectives ... 1 1.3 Challenges Faced ... 1 1.4 Literature Review ... 2SECTION 2—METHODOLOGY ... 3
2.1 Design ... 3 2.2 Implementation ... 4SECTION 3—RESULTS ... 8
3.1 Testing ... 8 3.2 Evaluation... 9 3.3 Competitiveness Advantage ... 9 3.4 Looking Ahead ... 9 3.5 Total Budget(Estimate) ... 9REFERENCES ... 10
LIST OF ILLUSTRATIONS
Figure 1. System structure...3
Figure 2. Front view of the First Generation...4
Figure 3. SIde view of the First Generation...4
Figure 4. Testing first Gen with passive actuator...4
Figure 5. Design View of first Gen in Solidworks...4
Figure 6. Front view of Second Generation...5
Figure 7. Side View of Second Generation...5
Figure 8. Design view of the initial driver module...6
Figure 9. Finished Driver Module...6
Figure 10. Finished Exoskeketon and Key Features...7
Figure 11. Stair-climbing testing with the current exoskeleton...8
SECTION 1—INTRODUCTION
1.1 Background
Although autonomous robots are being more and more widely used in the logistics industry for heavy lifting tasks and are promising a great reduction in man labor, it is still generally not available to most small and even medium-sized businesses due to the high financial and technological entry barrier. For both developing and developed companies, there is a need for man labor at the their neighborhood-level branches where workload is too small for large scale automation but unavoidable. As a result of this issue, a small number of workers will have to be positioned to handle daily tasks like parcel delivery and classification. During all the above tasks, there will be a considerable amount of tension (load, stress) on the back muscles of the worker, if not treated and relived properly and especially after a prolonged time, the workers will likely suffer from back pain[1] and
fatigue induced muscle damage.
The current situation calls for a technological solution to reduce the stress on the workers back during heavy lifting tasks. This project is going to attempt to developing such a solution. We will design, build, test, and study an exoskeleton robot that attaches to workers' bodies like a backpack and assist when needed to reduce the workload for the user. There are similar products in the market from various companies, apart from having each of their own limitations, they are all relatively expensive and unavailable to the general workforce. It was not until recently, due to technological advancements[2], the parts needed for such an exoskeleton had a
significant drop in terms of price and accessibility, making it possible to develop a new low-cost yet efficient solution. If successful, such a solution will be of great benefit to both the workers and the employers as the cost to provide insurance and medical care can be drastically reduced.
Another possible application of this project is to satisfying the increasing needs of assistive devices that arise from global population aging. With a slight modification, the project can be used to provide support and assistance with daily tasks such as lifting and stair climbing.
1.2 Objectives
In this project we will design and fabricate a low-cost powered exoskeleton aiming to reduce the stress level for workers during heavy lifting tasks. With the successful completion of the initial goals, the exoskeleton will need to make a considerable difference in terms of back muscle activities and the cost of the exoskeleton will preferably need to be relatively low, for example below HKD 5,000
Further studies after project completion can include industrial cooperation to produce and promote the product developed.
1.3 Challenges Faced
In the development process of this project, there were several technical and non-technical challenges that will need to be solved by the team. Technical challenges mainly relate to the effective acquisition of control signals from the user. We have changed our plans for control signal acquisition from EMG signals to gait pattern recognition by IMU signals due to the difficulty in acquiring good EMG signal readings and the difficulty in using and maintaining the sensors in daily use. However filtering and pattern recognition still have to be implemented on the IMU input signal which, although better in quality, is also affected by noise and bias. This posed a great challenge for the team, one that requires detailed study and experimentation. Non-technical challenges such as budget, development timeline, and component logistics will also be present and require careful planning and management. After sorting out these mentioned challenges, the team will be able to focus more on project development.
1.4 Literature Review
There have already been various studies and products in similar areas such as lower back support exoskeletons
[3], passive exoskeletons that provide thigh support, and ankle exoskeletons to reduce metabolic cost on
normal working without external power. There are also other products that provide gait support to those suffering from a stroke. There are companies from the USA and Japan that have already produced upper back support exoskeleton products and had multiple tests performed on these products. However, many of those products still have their limitations, which makes them a worse fit for the current industrial needs.
The car manufacturing giant Hyundai developed the H-WEX[4], which was demonstrated at the CES 2017 in Las
Vegas. Being significantly smaller and more practical than previous industrial exoskeletons by the car manufacturing giant, the H-WEX also has the benefits from easy control and simplified structural design. However, great limitations are placed on the H-WEX in terms of driving power. With power for both legs provided by a single motor, it was not able to completely support the user in heavy-lifting tasks. The user will still have to make a considerable effort in order to finish the task at hand. The stress on the user will be reduced but not eliminated, and fatigue can still occur after prolonged usage on the exoskeleton in working scenarios. This makes the H-WEX a choice that needs to be reconsidered.
Another example of similar technology is Back-X[5] developed by Suit-X, which is a novel industrial exoskeleton
that augments the wearer's strength and can reduce the risk of back injuries among workers. With a smartly designed adaptive structure, Suit-X doesn’t impede with natural movements of the user, which allows for a wide range of activities to be carried out while wearing Back-X. Able to work together with a body harness and other working equipment, it can be applied to industry swiftly. Despite having such advantages, Back-X is purely passive, which means that there is no power supplied to the exoskeleton at all, and the reductions in muscle stress come solely from the smartly designed support and energy reuse system. This can be useful in low-intensity daily tasks such as maintenance but will not meet requirements for heavy-duty tasks that are typical in an industrial setting.
Cyberdyne, the Japanese company famous for its development for the HAL Exoskeleton, also made a lower-back support exoskeleton named HAL-LB03[6]. The exoskeleton reads the bio-electric signals and assists the
wearer's movement according to his/her intention and reduces the stress applied to the lumbar region. The device can be used by all groups, including women and elderlies, thanks to its lightweight and compact design. Again, as this device only supports the lower back area, it cannot provide enough assistive torque to the user in lifting tasks. The lack of support for the upper back region means that all the assistive torque will be acted on the support belt located in the stomach region, which can lead to excessive compression for the internal organs and cause nausea. Unable to fix the rotation axis as the stomach can easily compress and shift the entire exoskeleton, there can also be risks of hip injury due to unnatural loading on the hip joint.
With a firm structure and powerful motors, this project design will solve the above-mentioned power and operation limitations of other similar products and provide a better solution to the industrial needs.
SECTION 2—METHODOLOGY
This section describes the detailed considerations and design process in the development of this project.
2.1 Design
The current software structure is as below:
*Components in the dashed textbox are still under development
2.2 Implementation
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:
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
The finished exoskeleton, together with its key features, can be found as the picture below:
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)
Table 1: Budget
Item Cost
Motors and ESC $2500
Gearboxs for motors $700
Frame Components $3000
Force Sensors $1000
CNC custom parts $2000
Parts tested but not selected $5000
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?)
