Biomechanics of Human Body Motion: Engineering a …

[Pages:23]1

Biomechanics of Human Body Motion: Engineering a Glove for Hand Motor Disabilities

Ezra Brooks, Justin Perez, Ilse Sweldens, Annie Wang, Lucy Zhang

Mentor: Catherine Connolly RTA: Eamon Collins

Abstract

Using SolidWorks, a threedimensional engineering design program, a glove was created to help people with fine motor skill impairments maintain a desired hand position. The glove, in order to hold the hand in the specified position, is rigid, but it features locking mechanisms on the finger joints that enable users to adjust it into whichever hand position is needed. Poor fine motor abilities are highly prevalent due to a range of neurological and physical disorders. The glove was designed to assist patients in basic hand functions such as writing; the prototype model is dimensioned to fit the hand of a child at the age where writing skills are developing. The glove's locking mechanism allows for patients to achieve easily adjustable hand positions. SolidWorks was used not only to design the glove, but also to create an animation of the assembly of the device, to produce engineering drawings, and to simulate the effects of forces on the pieces.

1. Introduction

Hand motility is a crucial aspect of human function and occupies a significant portion of the brain's processes Hands are

capable of touching, grasping, feeling, manipulating, and more. However, many people are unable to fully utilize their hands due to disabilities; 22% of children in second grade have dysgraphia, the inability to write properly.1

The following chart depicts the normal progression of motor skill development for young children. Conversely, children with impaired physical abilities have delayed development.

\

Figure 1: Development of children including fine motor2

Dysgraphia results from flawed motor and information processing skills such as visual-spatial and language processing. Symptoms include illegible

handwriting and awkward pencil grip and position. Issues with writing and other fine motor skills can affect people of all ages, and can result from various conditions. Dyspraxia is a neurological disorder throughout the brain that inhibits motor skill development.3 Autism spectrum disorders and attention deficit hyperactive disorder can also lead to motor skill defects. Parkinson's disease creates tremors that can greatly inhibit hand motion.2 Cerebral palsy, a physical disability that affects movement and posture, can weaken muscle control, muscle coordination, and balance.4

From a purely physical perspective, the primary cause of fine motor control problems is a lack or overabundance of muscle mass.5 Children in particular may have low muscle mass and thus struggle to maintain control over something as simple as a pencil or scissors. Genetic and environmental factors are also causes of these motor skill impairments. Further, premature children of substance abusers are at high risk for this condition. Likewise, people who have undergone certain types of surgery frequently have trouble regaining physical coordination, resulting in difficulty controlling the fine motor skills of their hands.

A glove that stabilizes the hands would mitigate the effects of these disorders, improving the hand function for people with impaired fine motor skills. By supporting the hand with a specially designed glove, patients should be able to improve hand motility, rendering activities such as writing and holding utensils easier. In addition, wearing the glove for an extended period of time would allow muscle memory to

2

develop, so the patient would be able to instinctively be able to remember the correct positioning for holding pencils, or utensils.

2.Fine Motor Skills and Hand Data

2.1 Fine Motor Skills and Children's Writing Ability

Fine motor skills affect a person's ability to hold, to pick up, or to move objects. Often, impaired fine motor skills result in a social stigma, as young children are unable to perform basic tasks. Problems related to fine motor skills are common, as about 20% of children are affected with dysgraphia, the inability to write correctly, legibly, or, in some cases, at all.6 These skills develop slowly as children age, but can often be overcome with practice. However, if unaddressed, these problems may develop into chronic diseases that can cause many difficulties later in life.

Currently, the side effects of impaired fine motors skills are difficult to alleviate. Children who struggle with writing are given rubber pencil grips and larger pencils that help students assume the proper writing position. However, these methods merely skirt the issue, without addressing the actual problem, the improvement of fine motor skills. The children will still struggle to use normal pencils in the future, as this is not a permanent fix. For others with disabilities such as autism or cerebral palsy, trainers and aides often use a hand-overhand7 method in which they guide the patients hand into forming proper grips and

motions to grab and use items. This method is not entirely effective because the trainer's grip is not entirely rigid and it cannot be used when the trainer is unavailable. Another attempted solution is the weighted glove.8 These gloves provide stability and target fitness, but make basic hand motions more difficult largely due to the added weight that requires greater hand strength to achieve the same functionality as one who does not use the gloves.

Children are given toys and worksheets that focus on fine hand movements, mainly line tracing. These methods focus on training, but do not give the basic structure or technique necessary to easily learn fine motor skills. Therapeutic weighted gloves contain weights on the top of the hand. However, these weights must be adjusted when the hand position is changed, resulting in both inconvenience and potential pain.

Figure 2: A weighted glove9

The other problem is the lack of proper writing technique. Most people do not hold the pencil in the optimal position for writing efficiently and clearly. The

3

pencil is supposed to be held between the thumb and index fingers alone. 7 Further, the pencil should be moved through the use of shoulder, back, and forearm muscles, as opposed to the fingers. This problem is caused by the lack of good instruction of writing techniques as well as the lack of a good guide for how to hold a pencil.

2.2 Conditions Related to Poor Fine Motor Skills

Many diseases that impede motor development are neurological. For example, dysgraphia often overlaps with other learning disabilities such as cerebral palsy and autism. Brain surgery also creates side effects that affect motility. To prepare for surgical procedures, surgeons often use anesthesia, which generally alters pain perception, aids muscle relaxation, and induces a state of unconscious throughout the body. Motor skills can be temporarily impaired after anesthesia.10 Similar side effects are also common after cancer treatment such as chemotherapy.

Cerebral palsy is also a consequence of damage to parts of the brain that manage motor movement, rendering the brain incapable of sending the appropriate signal to muscles to make them move properly. The specific damaged sections of the brain determine the type of cerebral palsy that the individual develops. Severely afflicted individuals may have uncontrollable hand motions.

For diseases that do not affect the nervous system, muscle memory provides a physical method that can make the effects of temporary solutions permanent. Muscle memory is stored in the brain as a form of

4

procedural memory that improves ability through repetition. Muscle fibers maintain a long lasting structural change.

2.3 Anthropometric Data

Anthropometric data describes average human body measurements and proportions for a population. In this study anthropometric hand data was utilized to ensure that the glove would fit the average child in need of fine motor skill aid. The standard deviation of the measurements is also included in Appendix A, and its small values show that the glove would fit the vast majority of children in need.

Figure 4: Joints in the hand12

2.4 Joints Responsible for Writing

Position

The primary joints that determine the

hand's position while writing consist of the

carpometacarpal,

metacarpophalangeal

(MCP as shown in the yellow arrow), and

proximal interphalangeal (PIP as shown by

the blue arrow) joints. The hand joints,

wrist, and bone account for the body's

support and flexibility to manipulate objects,

rendering the stability of the joints as

imperative.

Figure 5: Primary hand muscles13

Figure 3: Hand Skeletal Structure11

3. The Design Process:

Brainstorming, Drawing, and Modeling the Glove

3.1 Experimental Procedure

In determining what biological disorder to target, general ideas were discussed based on common diseases as well as personal experiences. An article on a possible alternative to using drugs provided an example of a product that started as an ambitious idea and is still in the research and developmental processes. However, one of the main hindrances to the brainstorming process was the lack of technical and scientific knowledge, eliminating many possible ideas such as miniaturizing monitors and dialysis machines to fit inside the body.

Once the glove idea was chosen, it had to be designed in more detail and drawn on graph paper with dimensions. The first step taken was to determine the target audience of the glove, which was deemed to be people with fine motor skills impairments. The glove focuses on the physical and mechanical aspects only, using a rigid yet dynamic adjustable brace to lock the fingers into specified positions. It was decided that the prototype glove would help young children with basic functions such as writing and holding utensils since these essential skills should, ideally, be learned and addressed at a younger age. The glove would also ultimately allow for more independence and confidence for patients with fine motor skill disabilities as well as provide enough support so that patients may be able to use muscle memory to correct their positions.

5

Next, ideas were developed for the glove's locking mechanism and structure, the most important components of the glove. Both the functionality of the glove and the appeal to the possible customers were considered in the design. A completely rigid glove with fixed fingers was considered at one point, but it would mean that the glove could only be used to help patients with one problem. In addition, it would be difficult for people to fit their hands into a glove already in the proper writing position. For the locking mechanism, the first general idea was to allow movement for all the joints. A couple of ideas were considered, many taken from moving joint parts on knee braces, but they were all variations of the same basic mechanism: a locking mechanism that kept the fingers in a position through interlocking gears placed at finger joints.

Figure 6: The initial hand-drawn sketch

A rigid yet flexible structure was ideal for the glove frame because it would keep the hand in place but still allow for some mobility of the joints and fingers to avoid cramping and general discomfort. Modeling the plastic pieces after the bone structure of the hand was done because it would be more helpful as a guiding device as it would simulate an actual human hand. The attempt to use a type of hard plastic as opposed to rigid metal aimed to make the glove more lightweight. A problem that was later addressed was the movement of the

thumb, which usually requires more mobility and dexterity than the other fingers do. It was debated whether or not a piece specific to the thumb should be designed to allow for maximum rotational and mobile functionalities, but it was challenging to incorporate all the additional parts into the design considering the added weight as well as placement and design possibilities. However, because the positioning of the thumb is similar when writing and eating, it was decided that the thumb's PIP would be kept entirely rigid with a solid plastic ring.

Although the glove was intended to target children and patients of all ages, the prototype was chosen to be modeled for a seven to eight year old child, mostly for convenience for 3D printing. Hand anthropometric data for children aged 7.58.5 from a study in Britain was used to devise finger measurements for modeling, as shown in the charts Table 1 in Appendix A. Because the anthropometric data only included measurements for the first three fingers and the lengths and diameters of those, there was a lack of data on the ring finger and pinkie and distance between finger joints. As a result, detailed measurements were taken of each group member's hands, and the ratios of the lengths of distances between joints were calculated and averaged to compensate for the lack of researched data. According to the data chart in Appendix A, Part 1 refers to the length of the hand starting at the wrist and ending at the knuckles. Part 2 of each finger refers to the distance between the knuckle and the middle joint. Part 3 is the distance between the middle joint and the

6

last joint, where the glove will end in a velcro-adjustable strap.

As the brainstorming progressed, the basic functions of SolidWorks were learned in preparation for the modeling of the glove design later on. Two-dimensional functions, such as sketching shapes, creating dimensions, and assigning constraints, were essential for defining and constructing the various shapes necessary for the glove design. The four major 3D features, extrusion, loft, revolve, and sweep, could be manipulated to create the three-dimensional figures from the 2D sketches. After these skills were mastered, the assembly feature was learned. The gearbox that was created had parts that were fully constrained along with parts that were intentionally partially defined to allow for motion. The assembly feature allows for the different parts, made separately for precision and efficiency, to be attached to each other to construct a complete model.

After discussion of the locking mechanism, thumb mechanism, and dimensions with the project mentor, modeling the device on SolidWorks began. At the beginning, everyone experimented with creating new parts on SolidWorks to test the easiest and best ways to construct the different parts including the locking gears as well as the thumb and wrist pieces. Once the more complicated pieces were created, the remaining tasks were split among the group members due to the limited time available and the amount of work left. Some group members continued to work to refine and complete the existing parts while others created rudimentary models and worked on the engineering drawings,

analysis reports, and animation of the 3D model in SolidWorks.

3.2 Physical Description of the Device

Figure 7: A 3D Model of the glove

The glove has a fingerless fabric piece covered by rigid plastic supports. The plastic used is ABSplus-P43014, a production-grade thermoplastic used with Dimension 3D Printers.

The supports begin at a plastic wrist brace and follow the skeletal structure of the hand, with one support for finger including the thumb. The supports ends anterior to the distal interphalangeal joint, leaving the fingertips free for comfort and grip. They end in a slit for a Velcro band to wrap around the finger. At the two joints, the metacarpophalangeal and proximal interphalangeal joints, there is a gear shell

7

that allows rotation of the finger joint, but can provide rigidity at any angle of rotation.

For the most effective application, the gloves are adaptable to different hand conformations, but are rigid in the selected one to provide the support and structure necessary for improving fine motor skills. In order to achieve this, the gloves have small gear knobs above the joints, which are shown in Appendix B.

Within these knobs, two interlocking gears are layered next to each other vertically. These gears are rigid, but have inward teeth that allow interlocking. For the easiest modeling, these gears are 20-sided polygons. The left gear (assuming a right hand glove) has a central hole for a push button. This gear also has a circular ridge extrusion at its base that sits on an inverse ridge in the shell. The hole is filled with a cylinder connected to the right gear. This gear sits on a small spring. As the digit is moved, the right gear rotates, clicking into place, maintaining rigidity. In order to unlock the gears, the cylinder button is pushed in so the two gears' teeth unlock allowing rotation back to normal hand position. The cylinder button must be pushed in to rotate the joint in either direction because the teeth are not sloped, ensuring full rigidity in any position. This mechanism sits slightly anterior to the top of the knuckle.

Figure 8: Index finger brace 1.

Figure 9: Shell

The shell mechanism is a basic hollow cylinder with a hole for the button at one end and a rigid base with an extruded circle for the spring to sit in at the other end. The shell has two slits in it that allow the finger plastic pieces to connect to their gears by a thin connector piece. The slit on the left of the right hand is fitted to the small plastic connector, whereas the slit on the right extends down on the opposite side around 180? to allow for the joint to rotate with the bottom gear. The mechanism has a length of 7.5mm and a diameter of 5mm.

Figure 10: Wrist and thumb brace

However, the thumb requires a different approach. The distal phalanx of the thumb has an extremely minimal range of motion. Conversely, the remainder of the thumb is capable of a wider range motion, powered by several strong muscles,

8

including the abductor pollicis brevis, the abductor pollicis, the first dorsal interosseous, the flexor pollicis brevis, and the opponens pollicis.15 To enable the thumb to adjust positions while still maintaining rigidity, a similar locking mechanism to the one described before is attached to the hard plastic structure around the wrist, right above the carpometacarpal joint. The original mechanism is simply rotated onto its side with the button facing upward, and the shell is mounted on the wrist brace. Furthermore, a hard piece of plastic is attached from above the extrinsic thumb muscle to above the intrinsic thumb muscles, restricting the thumb's motion. This piece of plastic follows the thumb's straight conformation to before the nailbed ensuring full thumb rigidity.

Designing the glove structure on SolidWorks required slight revision of the original sketch. The actual skeletal structure that functions similar to braces was created such that the bottom portion has a rounded surface while the top surface is flat, as to simplify the addition of the locking mechanism on top. The gears in the locking mechanism have differing teeth, trapezoidal teeth on the gear closest to the cylinder and the rectangular teeth on the mobile gear. The differing types of teeth allow for the two gears to interlock precisely in the assembly function of SolidWorks. The shell in which the locking mechanism is contained required little alterations. The slits which allow for the plastic material to enter the shell and attach to the locking mechanism are also of differing lengths, one that allows for extensive range of finger motion and one simply to keep rigidity. The longer slit

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download