Pneumatic Glove for Rehab

Stroke is ranked as the 2nd leading cause of death worldwide with an annual mortality rate of 5.5 million. Half 50% of the stroke survivors are left with a type of paralysis that affects their abilities to perform activities of daily living (ADL). Medically this paralysis is treated by rehabilitation therapies under supervision of health experts. But a patient’s adherence to these therapies is usually low due to the high financial costs and slow results. Therefore, rehabilitation procedures have integrated devices such as exoskeletons, pneumatically or hydraulically actuated gloves, etc. for home rehabilitation purposes.

Recently, there are a lot of researches on developing robotic rehabilitation systems for the hand that include multi-degree-of-freedom exoskeletons, The assisted robot for rehabilitation with rigid links provides robust applications capable of high forces and executing challenging rehabilitation scenarios. The hard exoskeleton is one of the assistive and rehabilitation devices used widely by stroke patients or people having problems with their hands. This tool uses almost rigid links for the robot. However, these rigid devices are a little heavy, expensive, and require care and time for proper alignment with the joints.

Another existing design of soft Pneumatic glove which is used for finger rehabilitation is GBBA (Guided Bending Bellow Actuator) Pneumatic glove which is actuated by elliptical cross-sectional guided bending bellows to augment finger-knuckle rehabilitation. These actuators are made using Thermoplastic elastomer (TPE) materials, providing controlled bending. It is found that they enhance finger movement range and strength more than exoskeletons. But their drawback is that there is a misalignment of the actuator on the finger joints and knuckles due to different hand sizes of patients and it is not that customizable, making it less effective in the rehabilitation.

Researchers have evaluated several different actuation techniques for soft robots over time and some of the most common ones include: pneumatics, hydraulics, electric motors, actuators based on shape memory alloys, and electro-magnetic soft actuators. Pneumatic and hydraulic based actuators share a common physical working principle: the application of an input force, provided by compressed air or other fluids, results in a deformation of their structures exerting forces on the external environment. Shape memory alloys (or SMAs) are materials that deform when exposed to heat: SMAs systems can be used in order to realize wide varieties of configurations due to their flexibility, but actuation is generally slow in time and complex to control. Electric motors driven systems are often based on flexible tendon connected to a linear or rotary motor, this choice allows precise and controllable movements. Electromagnetic soft actuators embed in their structure magnetizable elements that can either attract or repulse themselves resulting in a deformation of the device.

Another research on soft robotic gloves was based on a hydraulically actuated soft robotic glove that uses a fiber-reinforced elastomer actuator that can be mechanically programmed to create complex motions similar to a human finger. The main challenge involved in developing a hand rehabilitation device is that traditional robotic devices use actuators that are less compliant than the joints themselves. These devices tend to be heavy-weight and difficult to operate, minimizing patient use of these devices; especially in personal settings.

Over the years, numerous varieties of pneumatic soft actuators have been created, since these devices are low cost, relatively easy to realize, and they are particularly suitable for applications where there is an interaction with man due to their intrinsic compliance. Diverse constructive solutions given so far fall within the broad description of pneumatic soft actuators, and they can be divided into the following four major categories: Pneumatic artificial muscles (PAMs, also known as McKibben muscles), fluidic elastic actuators (FEAs), also known as soft elastic actuators (SEAs), such as Pneu-Nets actuators or soft bending actuators (SBAs), fabric-based actuators, and finally 3D printed actuators are examples of artificial muscles. This report is focused on the design and production of a pneumatic soft actuator; more specifically, a silicon PneuNets design based actuator.

PneuNets (pneumatic networks) are a class of soft actuator that are made up of a series of channels and chambers inside an elastomer. These channels inflate when pressurized, creating motion. The nature of this motion is controlled by modifying the geometry of the embedded chambers and the material properties of their walls. When a PneuNets actuator is pressurized, expansion occurs in the most compliant (least stiff) regions.

Components used in the control system for controlling the Pneumatic Soft Robotic Hand are listed as follows:

1. Arduino Mega controller

2. Air valves

3. 100KPa Air pumps

4. 12V 3s Lipo Battery

5. 2-motor driver (LM298N board)

FINAL ASSEMBLY

The setup of an air pump requires an external power supply to manage the flow of current to the pump. The pumps we used are not bidirectional, that means we needed 2 pumps linked by splitter to control both inflating and deflating of the actuators. But we controlled this using air valve itself as we left 1 port of valve open, which allowed the air to come out. One end of the actuators is sealed with silicon tubing and these actuators are mounted on the fabric glove and connected with this control system, making it a portable, light-weight and easy to use rehabilitation device.

o Added/ Inserted the whole control system in a 3-D printed case made using 3D printing with PLA White filament, thus making it portable.

o Soldered the connections -Pins are on the base of the air pumps. So we wrapped the wire through the small hole, added a blob of solder and trimmed the excess wire to prevent shorts. Gave the wires a gentle tug to make sure they are properly secured.

o Added a switch - for automatically controlling the inflation and deflation of the actuators.

o Actuator assembly with glove- To interface with the patients, the five pneumatic actuators were strategically placed on the cotton glove to align with the finger positions, ensuring each actuator can replicate the bending and extension of the corresponding finger. The actuators were securely fixed onto the glove using the Silpoxy glue. Once the actuators were attached, the glove was tested by holding different objects of varying sizes, ensuring the glove could provide the desired rehabilitative motions.

Final Prototype and Test Results

To interface with the patient, the actuators were attached with Silpoxy glue to the cotton fabric light-weight glue (or also can be attached using thin Velcro straps to an open-palm glove, made of an elastic material) that would conform well to the hand at all bending angles.

GRASPING TEST - The grasping force of elastic pneumatic finger can easily be controlled by adjusting the flow control valve to change the supplied air pressure.

We performed the experiment to check the ability of the soft pneumatic robotic glove to hold objects. We tested the pneumatic glove by holding and grasping the objects of different sizes and shapes, weighing from 30 grams to 200 grams. Experimental results showed that the soft pneumatic robotic glove lifts small and medium-sized objects from 30 grams to 180 grams. However, for a heavy target weighing >280 grams, we can still maintain lifting the object for a short time (about 5 seconds) since its weight is larger than the soft fingers pressure force.

Conclusion

Advances in soft materials and rapid prototyping is playing the key role in rapid development and improvement of soft robotic rehabilitation devices. This report presented the pneumatically actuated soft robotic glove fabricated with combination of low cost silicon and an inextensible material. Pneumatic pressure is responsible for flexing and extending of actuator. This soft pneumatic robotic glove thus can be used for hand rehabilitation purpose for the patients having some injury or stroke. We did the experiments with soft fingers to figure out the force and the largest bending angle. The soft fabric glove was connected with the soft finger by Silpoxy. Each soft pneumatic finger can achieve high force with high pressure for hand contractility.

A soft robotic glove is highly safe for people than a robotic hand with rigid links and lighter weight with the same function. This paper presents a cost-effective, portable and customizable pneumatic hand glove design which can be further refined for its application in the medical field. The cost effectiveness of the solution can be explained in terms of the fabrication of PneuNets actuators, which was done using silicon rubber that is widely available in the market at low-cost.

In the future, soft gloves could be developed that can grasp anything for the people that lost the handling ability. The results highlighted the potential of soft robotics for applications like rehabilitation devices, offering safe, accessible and adaptable solutions for human-machine interaction. In conclusion, hand rehabilitation will bring many benefits to patients with high recovery ability.