Force Required
In order to facilitate rehabilitation, an important function of our device is to open the hands of patients who experience spasticity. To do this, our device must be able to overcome the muscle tone in a spastic patient’s hand.
At the moment, we are not able to find the exact data for the average force required to open patient’s hands. Furthermore, the force required varies from patient to patient. We have consulted the literature available, and have found the data in the graphs below. In the graph, we can see the range of grasping force that patients with spinal cord injury is able to produce with their hands (without Exoglove Poly [EGP]). Although this does not directly represent the force required to open spastic hands, this is the best estimate we can find so far and it is likely to be more than the natural force of the spastic fingers as the patient is attempting to grasp objects in this case. As can be seen, the grasping force ranges from 0.5N to 3N.
Figure 1: Results for the grasping performance of two spinal cord injury (SJI) subjects. The red bars represent the force required to pull an object from a subject’s hand without wearing Exo Glove Poly II (EGP), which we see as an estimate of the force required to open a patient’s spastic hand. [1]
While our main goal is to focus on rehabilitation, our glove could be used in future to assist patients in carrying out activities of daily living (ADL). In order to handle the heaviest objects involved in daily life, the assistive force that each finger should exert must be more than 9.8 N [2].
As a preliminary test, we decided to find out how much force the motors we purchased could handle. We started off with a 1kg weight attached to the motor. Although the motor was able to move the object, the motor seemed to have been spoiled after the test and started to move even though the program told it stop.
As such, we subjected the motor to less force instead, attempting to use 6N of force instead. While this amount of force may not be sufficient to carry the heaviest objects in daily life, it is sufficient to open patients with spastic hands. The set-up of our test can be seen in the video below:
As seen from the video, the weights dropped to the floor after a while. This was not due to the weakness of the motor, but due to the weakness of the spool we attached to the motor. It was 3D printed and had an hollow centre which led to weakness. As such, we can conclude that the motor is able to handle at least 6N of force.
Moving forward, we will improve on our spool design to manage the force that the device would be subjected to. For instance, we will print the spool with a solid centre instead.
References
[1] Kang, B.B., et al., Exo-Glove Poly II: A Polymer-Based Soft Wearable Robot for the Hand with a Tendon-Driven Actuation System. Soft Robot, 2019. 6(2): p. 214-227.
[2] R. Takashima, H. Kawamoto and Y. Sankai, “An ultra-multijointed assistive robot finger,” 2017 IEEE International Conference on Robotics and Biomimetics (ROBIO), Macau, 2017, pp. 538-543. doi: 10.1109/ROBIO.2017.8324472