**7. Discussion**

162 Haptics Rendering and Applications

duration time of "viscosity" is -2.31 sec and that of "assistance" is -9.76 sec. The average RMS error of "viscosity" is 0.38 mm and that of "assistance" is 4.89 mm. In both cases, the




Difference of Time (sec)

Fig. 14. Relationship between the difference of duration time and difference of RMS error of

A post-experiment interview was carried out for all subjects. 19 subjects answered the question "How was this game?" The subjects could answer freely about her or his impression of the experimental program. The vocabulary of their explanations was limited because they were young. The most common answers were "fun" (12 subjects), "interesting" (9 subjects), and

Two subjects gave both positive and negative impressions. Subject A (age 4 years 9 months, male) said, "Fun, but one of the pre-experiment programs was not interesting. It was too easy." Another subject B (age 5 years 8 months, male) said, "Fun, but I was tired." Subject A moved the grip quickly and finished tasks more quickly than average. In contrast, subject B moved slower than average and had less error than average. However, in the case of "assistance", subject B moved quickly and the error increased. This could be a sign of

Simple questionnaires were also used. We asked two questions: "Are you good at sports?" and "Are you good at TV games?" The subjects were categorized into a "good at" group and a "not good at" group. Table 3 shows the comparison of the group results and the average results. There are no significant differences. However, the "Good at Sports" and the "Good at TV Games" groups tend to have a shorter duration time than that of the "Not Good at Sports" or "Not Good at TV Games" groups. Due to the shorter duration time, the RMS error of the "Good at" group is larger than that of the "Not Good at" group. The "Good at Sports" group and the "Not Good at Sports" group can generally be expressed as "active" or "non-active" personality groups. The tendency of their motions may be quick, however the results are a shorter duration time and a larger RMS error. The "Good at TV

"easy" (3 subjects). All subjects who gave an answer had a positive impression.

0

5

10

15

Assistance Viscosity

20

significant difference was confirmed by a T-test (p<0.05).

R² = 0.3999

Difference of RMS (mm)

"viscosity" and "assistance"

**6.2 Interview** 

fatigue (Table 2).

R² = 0.1325

No correlation was found between the age and the duration time. The assumed reason is the range and the variation of the subjects' ages. Some younger subjects could not clearly understand the instruction, "Keep cursor (starfish) inside the thick wavy line" and operated it impulsively. Some older subjects understood the purpose of the program, "Try to keep moving the cursor on the center of the thick wavy line" and tried to do it carefully. Therefore, when the subjects are younger or they are not developing as expected, the experimenter should explain the task using easy words and be careful to make sure the subjects understand.

In the comparison between "no force applied" and "viscosity" or "assistance" applied, the duration time with the "assistance" force was shorter than that of the other cases. In the "assistance" case, it was observed that the upper limb of the subjects seemed to be pulled by the haptic device. Thus, the "assistance" force may prevent voluntary motion. However, for children who have problems with voluntary upper-limb movement or hand-eye coordination, the guiding force can help move her or his upper limb (grip) to the designated point. This assistance can stimulate motion and cognitive function. The suitable level of assistance and how it is involved in therapeutic training should be discussed in the future.

The error of motion decreased according to age. It was confirmed that error and age have a negative correlation. From observations, it was also confirmed that most of the older subjects tried to move the cursor along the center of the thick wavy line in the "Starfish" program. Thus, the results were reasonable. However, children at 5 years of age start to write Japanese characters and Arabic numbers as preparation for elementary school. Therefore, a simple line-drawing task should be easy for them to understand.

The negative correlation for the duration time and the grip position error was confirmed in the two different cases of applied force and no force applied. The tendency was the same as that in previous research for young adult to elderly subjects. To move the cursor in a smooth and fast manner, the subject must see the cursor, recognize its position, and move the

**9** 

**Development of a Detailed** 

*1National University of Singapore,* 

*2Nantong University,* 

*1Singapore 2China 3Portugal* 

Kim Tho Huynh1, Ian Gibson1,3 and Zhan Gao2

*3Centre for Rapid and Sustainable Product Development, Leiria,* 

**Human Spine Model with Haptic Interface** 

The human spine is an important structure, providing strength and support as well as permitting the body to bend, stretch, rotate and lean. It is also a vulnerable part of our skeleton open to disease and injuries like whiplash, low back pain, scoliosis etc. Whiplash is a frequent consequence of rear-end automobile accidents and has been a significant public health problem for many years with injury to one or more ligaments, intervertebral discs, facet joints or muscles of the neck. Low back pain is a very common disease and strongly associated with degeneration of intervertebral discs (Luoma et al., 2000) seen in people with sedentary jobs spending hours sitting in relatively fixed positions, with the lower back forced away from its natural lordotic curvature. This causes health risks of the lumbar spine, especially for the three lower vertebrae L3-L5. 80% of people in the United States will have lower back pain at some point in their life (Vallfors, 1985). Scoliosis is a less common but more complicated spinal disorder, being a congenital 3D deformity of the spine and trunk affecting 1.5-3% of the population. In severe cases, surgical correction is required to stabilize the scoliosis curvature. Studies into the treatment of these spinal diseases have played an important role in modern medicine. Many biomechanical models have been proposed to study dynamic behavior and biomechanics of the human spine, to develop new implants

Biomechanic models can be divided into four categories: physical, *in-vitro*, *in-vivo* and computer models. Computer models have been extensively used because they can provide information that cannot be easily obtained by other models, such as internal stresses or strains. They can also be used for multiple experiments with uniform consistency, lowering experimental cost, and simulating different situations easily and quickly. Multi-body and finite element models, or a combination of the two are the most popular simulation tools

that can contribute significantly to our insight of the biomechanics of the spine.

and new surgical strategies for treating these spinal diseases.

**1. Introduction** 

**2. Related works** 

direction of the cursor by moving his or her upper limb to the appropriate position. Usually, this ability is obtained by visuomotor experience beginning at birth. Moreover, improved and refined actions increase with the increase of experiences. In many cases, developmental disorder children lack many skills. They have a problem with hand-eye coordination due to their learning difficulties and lack of sensory-motor experiences. From the viewpoint of occupational therapists, upper-limb motion depends on stability and control of the trunk and shoulder. Therefore, they focus on improving posture, stability, and shoulder control before using therapeutic tools. During operation of the haptic device system, the users held their trunk in median antigravity. The upper limb was held in the air, and the fingers were used to hold the grip. Shoulder and elbow joint motion were involved with the motion of the grip. Especially, moving one's hand on a smooth curving trajectory, as in the experimental programs, requires coordination of multiple functions, direction control by the shoulder joint, and position adjustment of the elbow joint. Thus, the haptic device system, which uses upper-limb motion with visuomotor involvement, can be effective for hand-eye coordination training.
