Human operation in space over long time periods causes bone and muscle deterioration, so there is a need for countermeasures in the form of physical exercises consisting of working against controlled resistivity. Generally, there are three types of exercise machines that are used by space crews to maintain their fitness: the Crew Exercise Vibration Isolation System (CEVIS), the Treadmill Vibration Isolation System/Second ISS Treadmill (TVIS/T2), and the Advanced Resistive Exercise Device (ARED). These machines have the limitations of very large mass (some weigh about a ton), large operational volumes, cumbersome design, and the need to compensate the generated vibrations and large shifting of the center of mass. They also require interrupting the astronauts’ duties to perform the exercises, as well as requiring periodic costly maintenance. The disclosed de vice provides key elements to enabling the design and operation of compact exercise machines that overcome many of the disadvantages of the current exercise machines found on space vehicles/stations.
Various machines have been developed to address the need for countermeasures of bone and muscle deterioration when humans operate over extended time in space. Even though these machines are in use, each of them has many limitations that need to be addressed in an effort to prepare for human missions to distant bodies in the solar system.
The need for an exercise exoskeleton that performs on-demand resistivity by impeding applied forces and torques involves the development of a novel Electro-Rheological Fluid (ERF)-based device. The resistive elements consist of pistons that are moving inside ERF-filled cylinders. The piston consists of electrodes set with very small gaps between them, and allows the flow of ERF through the piston. The fluid flows through the piston when the piston is displaced and the electrodes are not energized.
Once the electrodes are activated, the electric field between them changes the viscosity of the ERF fluid and the piston resists motion. Moreover, if the electrodes are activated and the system provides high pressure on one side of the piston and low pressure on the other, the piston turns into a linear or rotary actuator depending on the specific implementation. Tests of the operation of ERF against load that were done in cooperation with Northeastern University showed the feasibility of this approach. To enhance the operation of this mechanism, it is essential to create a pressure difference between the two sides of the piston. The disclosed hydraulic system provides a pressure stepping method that addresses this need.
To increase the stiffness/resistance bandwidth, ranging from free flow to maximum viscosity, multiple electrodes are used to create the piston. In order to enhance the resistive force that can be obtained by this mechanism, input and output pumping nipples are added to the cylinder to allow entry of fluid to the side that needs to have increased pressure, while removing fluids from the other side of the piston. In this way, the actuator turns from a resistive element into an active element, creating linear or rotary motion, depending on the implementation. This use of pumping allows enhancing the impending force, and enabling, with the aid of an actuator, to augment the user lifting capability with a force that can be as high as 700 N. The pumping action needs to be controlled while synchronizing it with the movement on the exoskeleton. This system was inspired by the human body’s heart and blood circulation system, where separate high- and low-pressure tubing lines are used. The flow necessary to actuate the ERF-based elements is provided by mini-pumps and is assisted by a hydraulic pressure distribution system. The resultant force and the velocity of the piston are dependent on the electrical field strength and the flow rate of the pump. The flow rate is regulated by a servo amplifier that controls the velocity of the pump. The system controller is designed to synchronize the operation of the ERF device with the user performance. Also, sensors are used to provide feedback to the controller.