Full analysis of prosthetic activity level and its related elements

Prosthetics play a vital role in helping amputees regain their mobility. Their activity levels are clearly classified and are affected by a variety of factors. In the future, there are also exciting technological breakthroughs in the field of high-activity level prostheses.

1. Classification of activity levels of prostheses

Low activity level prostheses:

Mainly suitable for groups with low activity needs, such as some elderly people and amputees with poor physical condition. This type of prosthetic limb has limited mobility and can only support basic daily activities. For example, it can achieve slow walking movements and complete simple transitions between standing and sitting postures. In daily life scenarios, it is mainly used for short-distance movement indoors, such as short-distance walking from the bedroom to the living room, and some simple self-care behaviors, such as dressing and dining by yourself. However, for activities that require a high range of motion and strength, such as stair climbing and running, low-activity level prostheses are difficult to cope with.

Medium activity level prostheses:

Compared with low activity level prostheses, their functions and applicability have been significantly improved. Have moderate ability to walk and go up and down stairs, with enhanced stability and flexibility, able to meet a certain degree of daily activities and light exercise needs. Users can use it for walking, shopping and other activities outdoors, as well as short-distance jogging on relatively flat ground. At the same time, they can also complete some simple housework, such as sweeping the floor and wiping the table.

High activity level prostheses:

Specially designed for amputees who have high requirements for mobility. It has excellent stability, flexibility and strong strength, and can adapt to high-intensity sports and complex activities. Whether it's running, jumping, climbing or other challenging activities, it can handle it. These types of prostheses are mostly made of advanced technology and materials to ensure reliability and safety during high-intensity activities. It is suitable for athletes, outdoor enthusiasts and other people. They can freely participate in various sports activities, such as basketball, football, tennis, etc. Even in some complex work scenarios, such as carrying heavy objects and engaging in manual labor, high-activity level prostheses can also play an efficient role.

2. Factors affecting the activity level of prosthetic limbs

Design and performance of prosthetic limb components

Knee joint design:

The design of the knee joint has a significant impact on the activity level of prosthetic limbs. Compared with the single-axis knee joint, the four-link prosthetic knee joint has better bionic characteristics and movement safety. For example, in studies based on specific models (such as the Kelvin-Voigt model and Coulomb model to describe the foot-ground contact force and friction force, the Kelvin-Voigt model to describe the unilateral contact force of the knee joint, and the prosthetic limb dynamics model established based on the first kind of Lagrangian equation), it was found that factors such as the stiffness of the knee joint hydraulic damper will have an impact on the gait of the prosthetic limb. When the stiffness is small, strong nonlinear factors such as foot-ground interaction force will cause the prosthetic limb to produce a subharmonic response, resulting in detuning of the gait cycle. The hip-raising behavior can avoid this situation. In addition, prosthetic knee joints based on the magnetorheological effect have become a research hotspot due to their advantages such as fast response, continuously controllable damping, and low energy consumption. For example, the design of a new prosthetic knee joint that innovatively combines a four-bar linkage mechanism with a magnetorheological damper provides a new direction for improving the performance of prosthetics.

Hand joint design:

For prosthetic hand joints, the design of the composite drive fusion prosthetic hand joint is designed to meet the special needs of arm movement. It uses a composite drive method of memory alloy and motor to simulate the muscle movement of the elbow joint, so that the joint has compatibility characteristics while improving the drive performance. For example, in the design of multi-finger dexterous hands, an under-actuated method is used to drive finger movement with the help of memory alloy springs, and a special two-degree-of-freedom wrist joint is designed (such as using a magnetically controlled shape memory alloy clutch) to simplify the structure while ensuring flexibility.

Control methods and sensors

Prosthetic arm control based on inertial sensors:

Measure the wearer’s shoulder joint motion posture through inertial sensors, conduct online recognition of human movement intentions, and control the real-time trajectory of the prosthetic arm based on the shoulder-elbow-wrist mapping model to assist in completing upper limb movements. Experiments show that the average online recognition rate for multiple typical daily actions can reach a high level, and the real-time motion trajectory of the prosthetic arm has a small deviation from the normal human body motion trajectory, which verifies the rationality and feasibility of this control method.

Prosthetic knee joint control method:

In terms of prosthetic knee joint control, there is a trajectory tracking control method based on the motion reference curve. For example, in order to control the four-link prosthetic knee joint based on the magnetorheological effect, the MRFLPK trajectory tracking control principle based on the motion reference curve is used. At the same time, the motion reference curve generator principle based on the Rayleigh oscillator is used to provide the motion reference curve, and the calculated torque plus PD feedback control algorithm is used to achieve trajectory tracking control. In addition, in order to test related prosthetic knee joints, a rapid control prototype system was established that included lower limb prostheses, a control system, an angle sensor and a controllable current source. The control system was constructed by a real-time simulation system, which sensed the swing angle of the knee joint through the angle sensor. The real-time simulation system controlled the output current of the current source to change the damping force of the magnetorheological damper, thereby controlling the swing angle of the knee joint.

External environment and user factors

Foot-ground interaction force:

Taking a specific four-link knee joint passive prosthesis as the research object and using relevant models to describe the foot-ground contact force and friction force, research shows that foot-ground interaction force:

Strong nonlinear factors such as ground interaction forces have an important impact on the gait of lower limb prostheses. As mentioned above, when the stiffness of the knee joint hydraulic damper is small, it may cause problems such as gait cycle detuning.

The user’s adaptability and training level:

The early wearing of prostheses for walking by lower limb amputees is restricted by many factors, among which the user’s adaptability and training level play a key role in improving the activity level of the prostheses. After systematic and appropriate training, users can better master the skills of using prostheses, thereby improving the activity level of prostheses in actual use.

3. Prospects for technological breakthroughs in future high-activity-level prostheses

More precise nerve signal control:

Current research has made some progress in exploring the interaction between prostheses and nervous system signals. In the future, high-activity-level prostheses are expected to achieve more precise nerve signal control. With the help of advanced sensor technology, the electrical signals of spinal motor neurons are directly detected, making prosthetic limb control more flexible and precise. This will allow users to complete complex actions with their thoughts, such as accurately grasping objects of different shapes. At the same time, the development of advanced neural interface technology will closely connect the prosthetic limb with the user's muscles and nerves, not only achieving control, but also allowing the user to perceive feedback from the prosthetic limb, improving the naturalness and comfort of use.

Application of intelligent materials:

The application of new intelligent materials will bring changes to high-activity level prostheses. Materials with adaptive and self-healing capabilities can enhance the durability and reliability of prosthetics, automatically optimize performance based on the use environment and stress conditions, and improve stability and adaptability. In addition, this type of material helps achieve lightweight design of prosthetics, reducing the user's burden and improving mobility. At the same time, biocompatible materials can better integrate with human tissues and reduce discomfort and complications.

Advanced power system:

High-activity level prostheses rely on powerful power systems to support high-intensity activities. In the future, power systems will develop in the direction of miniaturization, efficiency, and intelligence. The application of new battery technology and energy recovery systems can extend the use time and improve energy utilization. The advanced motor and transmission system will provide more powerful power output and adapt to various terrains and activity needs. The intelligent power control system can automatically adjust power according to the user's movement intention and physical condition to ensure safety and stability.

Combination with artificial intelligence:

Artificial intelligence technology opens up new paths for high-activity-level prostheses. When combined with artificial intelligence, prosthetics can achieve autonomous learning and adaptive control. For example, by analyzing the user's movement patterns and habits, the control parameters can be automatically adjusted to better suit the user's needs. At the same time, artificial intelligence helps in fault diagnosis and predictive maintenance of prosthetic limbs, improving reliability and service life. Moreover, integrated with virtual reality and augmented reality technology, it can provide users with richer rehabilitation training and life experiences.

Personalization and 3D printing technology:

With the continuous advancement of 3D printing technology, high-activity level prostheses can be highly customized in the future. By scanning and modeling the user's body, doctors and engineers can design and manufacture the most suitable prosthesis based on individual needs and body characteristics. 3D printing technology can realize complex structure design and rapid manufacturing, improving production efficiency and quality. Personalized customized prostheses can better integrate with the body and improve comfort and stability.

In summary, prosthetic limbs have rich and diverse activity levels, and their development is affected by the interaction of multiple factors. In the future, technological breakthroughs in many aspects of high-activity-level prostheses are expected to bring unprecedented freedom of movement and improved quality of life to amputees.