Byungchul Kim, Hayejin Kwon, Mira Shin
After people have spinal cord injury, they cannot control their body easily. Assistive devices are one of the alternatives for clients to do activities of daily living (ADL). However, many users have various complaints about assistive devices to use in ADL because of appearance, weight, portability, and usability.  Among these devices, we focused on the writing assistive device which is called “penholder” to help clients who want to write.
Previously commercialized penholder fix the pen by putting in to a hole of the device. It is easy to fall out because of a low fix ability. User have to raise their whole arm while using because the pen shake a lot when clients lean their arm on the desk. This unstable posture applies high stress on the shoulder because of the weight of user`s arm. It can cause scoliosis too when the writing time gets longer.
To resolve these issues, we designed a new concept of the penholder that changes hand posture to tripod grasp. This tripod grasp enables users to lean their arm on the desk while writing, like the non-disabled. To achieve the tripod grasp we attached a single wire sheath on thumb, index, and middle finger. When the wire is pulled, wire tension gathers the three fingers into a single point.
In addition we designed thimble typed penholder that has fingerless glove and thimble, which improve the device conveniently while wearing.
There are lots of people who have spinal cord injury (SCI). Clients gets paralyzed some parts of their body because of the central nerve injury. Incidence rates of each country in traumatic SCI per year varied from at least 12.1 per million in Netherlands to 57.8 per million at most in Portugal. Most traumatic SCI studies showed two peaks in age distribution. The first peak was found in young adults between 15 and 29 years and a second peak in older adults (mostly ≧65 years), and also there were some statistical data which shows 55% of SCI clients are tetraplegia.  For constantly increasing clients with SCI, many assistive devices are developed, but they still have lots of problems. Among these devices, we focused on the device that assists hand function. We decided pen holder which assist pen grasping for young adults who have SCI.
Three fingers (thumb, index, middle finger) make tripod grasp to fix the pen strongly. With tripod grasp, arm can be placed on the table while writing to support the arm weight because of high fixability of the grasp. However, former commercialized penholders do not make tripod grasp. As shown in figure 1, posture to fix the pen is different from tripod grasp. Since this device is not customized to the users’ hand, the pen tends to move a lot when users lean their arm on the table due to the low fixability. Because users cannot lean their arm on the table, high stresses are applied to their shoulder. In addition, the device is difficult to wear because of rigid structure.
Problems of existing devices can be organized as follows
- Harmful while using: Difficult writing posture applies high stress on shoulder and scoliosis can be occurred in worse case.
- Convenience: rigid components of device drop portability (size and weight) and make hard to wear.
- Weak performance: When disturbance is applied to pen, pen position changes a lot because of low fixabilityy.
We tried to make new concept of pen holder to improve convenience while using. Most of former pen holders do not change the hand position actively. They fix the pen only using a hole. However, we designed to move finger actively to make specific posture. We used wire and glove to make device compact and light.
To realize tripod grasp, sheath should be attached at 3 fingers. As shown in figure 2, posture can change by tension of wire when the user pulls the wire. We decided to fix the sheath on finger part of the glove because clients usually use glove to diffuse pressure on their palm while riding the wheelchair.
Locking mechanism is necessary to sustain the tension of wire. Locking mechanism holds the wire using the friction force. While wire passes from fingertip to back of hand, wire direction changes about 90 degree. Grasp posture can be sustained with small friction force with this reason. To make friction force, we fixed sheaths on dorsal side of hand. The structure was inspired by small intestine to fix long sheath in a small place.
2 clients gave their opinions after using prototype of gloved type penholder. Below video shows the difference between former penholder and new one. Interview from two clients are also attached in the video. After interview, we developed next version of the prototype to improve convenience.
Thimble and wearing device
Design of penholder was changed after prototype evaluation. Design was focused on ‘Easy to wear’, because users commented that even though appearance, weight and performance are better than former devices, but wearing process is complicated. Fingerless glove and thimble were proposed for easy wearing process. Most of SCI clients use the fingerless glove to protect their palm when they handle the wheel of wheelchair. Figure 3 shows the total overview and principles of the wearing device system.
Discussion and Conclusion
Final product was evaluated to other three SCI clients. They gave various opinions for improvements. According to three consultant`s opinions, they could feel as non-disabled person while writing. Because glove type penholder changes their hand posture, they could use various pens with high grasp force, while previously commercialized penholders can only use several pens with same diameter. They felt dividing glove into fingerless glove and thimble also fulfilled ‘Easy to wear’ criteria. We could achieve our goals (Safety, Convenience, and performance) of this project with thimble type penholder.
To increase convenience of our product, we would upgrade locking mechanism to be semi-automatic or automatic. If locking mechanism is designed based on the idea of tapeline, user can pull the wire only in one way and unwind the wire by pushing the button. We developed this mechanism using a 3D printer as shown in figure4. We cannot use this mechanism immediately in this project because of durability. Ratchet structure was easily broken because of the weak property of the 3D printer. We could substitute this mechanism later.
In this project, only qualitative sides of the device were evaluated. We are going to have quantitative evaluation later. Impedance of posture, angle of each finger joints and accuracy of writing could be measured. We are going to measure these properties by 6 axis load cell (mini 40) and Vicon motion capture system.
Because there are many kinds of grasp in human hand, we can extend our device to cover other functions of hand by changing the path of sheath. Because we developed wearing device in this project, we could modularize other grasp method.
1 R. Wessels,B. Dijcks, M. Soede, G. J. Gelderblom, and L. De Witte, “Non-use of providedassistive technology devices, a literature overview,” Technology and Disability, vol. 15, no. 4, pp. 231–238, 2003.
2 M. E. L. Van Den Berg, J. M. Castellote, I. Mahillo-fernandez, and J. De Pedro-cuesta, “Incidence of Spinal Cord Injury Worldwide: A Systematic Review,” Neuroepidemiology, vol. 34, no. 3, pp. 184–92; discussion 192, Apr. 2010.
We`d like to thank our client (chihyun song), consultants (gwanghoon Chung, Chulhee You, Sunmi Cheon, Suho Park), advisor (Kyu-Jin Cho) and co-workers(Daeyoung Lee, Jisuk Kim) for developing this device.
This research was supported by and the Technology Innovation Program (10036459, 10036492) funded by the MKE/KEIT, Korea.