**3. Haptic device system**

#### **3.1 Hardware system**

Our haptic device system is intended for upper-limb rehabilitation. Fig. 1 shows a photograph of the proposed haptic device system. The system consists of a haptic device, a display, and a computer. The haptic device consists of two servomotors with reduction gears, link rods, a hand grip, and a flat panel. The grip and servomotors are connected by link rods. Patients can move the grip on the surface of the flat panel and train their upperlimb movements in horizontal.

The haptic device and the computer are connected by a USB interface. The moving range is 400 mm in the lateral direction and 250 mm in the longitudinal direction. The servomotors can apply a maximum force of 30 N to the grip. Optical encoders are attached to the servomotors. The position of the grip is calculated by the encoder pulse count and the length of the link rods. The LCD display shows the visual symbols of the training programs. The aspect ratio of the work field on the display is proportional to the actual flat panel. Advantages of the haptic device are ease of handling and portability in a hospital or a home. In this model, the user only needs to plug in the USB connector to a PC and run the training program. The computer executes the following functions:

Controlling the haptic device

152 Haptics Rendering and Applications

system and gather basic data for quantitative evaluation of the levels of disorders, we

In this paper, an outline of our developed haptic device system is introduced and experiments on the interactions of kindergarten children with this system are described. It was found that the proposed system effectively performed hand-eye coordination training.

For children with a development disorder, occupational therapy is usually performed. Occupational therapy for such children includes a variety of different therapies with many evaluation methods either proposed or existing. A suitable therapy provides individual

In the therapy for young children, the goal is to prepare them for elementary school. Of course, preparation requires many different actions. Occupational therapy is mainly focused on obtaining handwriting skills and self-reliance in daily life. Thus, the goals of therapy are enabling development of dexterous hand and visual perception. This means that hand-eye

In occupational therapy, many different tools are used, for example, toys, musical instruments, paper projects, mazes, and puzzles. Most of these tools are readily available in retail markets. Also, some are handmade by the therapist. These tools are used not only for therapy but also for evaluation the level of disorder. However, the evaluation of the effects are mostly based on the therapist's subjective observations and conventional pen-paper tests. At the present time, evidence-based occupational therapy is desirable. Therefore, establishment of quantitative evaluation methods are required. To meet this need, we apply

Additionally, therapists are interested in how to motivate patients and maintain the motivation for both children and adults. Virtual reality devices offering visual and sound experiences provide tactile and haptic sensations, which are interesting for patients, especially young patients. Therefore, we developed an effective haptic device system with training software that provides a haptic sensation on a hand grip held by the user. The

Our haptic device system is intended for upper-limb rehabilitation. Fig. 1 shows a photograph of the proposed haptic device system. The system consists of a haptic device, a display, and a computer. The haptic device consists of two servomotors with reduction gears, link rods, a hand grip, and a flat panel. The grip and servomotors are connected by link rods. Patients can move the grip on the surface of the flat panel and train their upper-

The haptic device and the computer are connected by a USB interface. The moving range is 400 mm in the lateral direction and 250 mm in the longitudinal direction. The servomotors can apply a maximum force of 30 N to the grip. Optical encoders are attached to the

carried out experiments with healthy child subjects.

therapy to treat the level of the disorder and the age of the child.

computer technology and virtual reality to conventional therapy.

sensation generated depends on the visual program.

**2. Research background** 

coordination is important.

**3. Haptic device system** 

limb movements in horizontal.

**3.1 Hardware system** 


Fig. 1. Haptic device system

Fig. 2. Flow of the haptic device system

Haptic Device System for Upper Limb and Cognitive

programs.

Fig. 3. Program selection menu

the target dot can be changed.

and radius of the circles can be changed.

**4.1 Training program** 

**4. Software for rehabilitation and evaluation** 

Rehabilitation – Application for Development Disorder Children 155

The software has two functionalities: training and evaluation. The training program consists of six different programs. The evaluation program consists of four different programs. When moving the grip, the cursor on the display simultaneously moves with the grip, and the haptic device provides a force that can either assist the movement of the arm or work against it. The level and the direction of the force are also adjustable. Moreover, the user can sense haptic perceptions such as contact force, viscosity, and surface friction. The data acquisition program runs with both programs and stores training data such as the time and the grip position. This data can be used in the quantitative analysis for motor control as well as cognitive function rehabilitation. Fig. 3 shows the program selection menu. The four icons on the left side are evaluation programs and the six icons on the right side are training

In the training programs, the user is urged to move her or his arms along diagonal, straight, and voluntary paths. The user can work a puzzle and play other game-like programs. These programs also help the user to develop concentration during training. Screenshots of the programs are shown in Figs. 4 to 7. Details of the programs are presented in the following. 1. Following the dot in the diagonal direction: White circles are positioned in the display in a diagonal position. A green target dot moves between two circles, and the user follows the target green dot by using the cursor. The color of the circles changes from white to red when the user attains the goal. The radius of the circles and the velocity of

2. Following the dot in the radial direction: Nine circles and nine line sets, which connect the circle in the center, are shown on the display. The user tries to move the cursor from circle to circle while staying on the lines by following the target dot. The displacement

3. Feeling the haptic force: Three subprograms to feel the difference of haptic sensations are prepared (Fig. 4). The sensations are spring force, viscosity force, and load (weight). Three different objects appear on the display and each object provides a haptic force. The user tries to touch and move the virtual objects and feel the haptic forces. The right

#### **3.2 Haptic force generation**

Six types of haptic forces can be provided on the rehabilitation system: load, assistance, spring, viscosity, friction, and special effects. The therapist can change the type and magnitude of the haptic force according to the user's level of disorder. The details of each force are described as follows.

1. Load: The load force is generated in the opposite direction of the grip velocity vector. The magnitude of the force increases in proportion to the distance between the current grip position and the target position. Load force Fl is shown in (1). When the grip position is (x, y), the target position is (x0, y0) and the gain is K1.

$$\mathbf{F\_{l}} = \begin{bmatrix} \mathbf{F\_{lx}} \\ \mathbf{F\_{ly}} \end{bmatrix} = \mathbf{K\_{l}} \begin{pmatrix} \begin{bmatrix} \mathbf{x\_{0}} \\ \mathbf{y\_{0}} \end{bmatrix} - \begin{bmatrix} \mathbf{x} \\ \mathbf{y} \end{bmatrix} \end{pmatrix} \tag{1}$$


$$\mathbf{F}\_{\mathbf{v}} = \begin{bmatrix} \mathbf{F}\_{\mathbf{v}\mathbf{x}} \\ \mathbf{F}\_{\mathbf{v}\mathbf{y}} \end{bmatrix} = \mathbf{K}\_{\mathbf{v}} \begin{bmatrix} \dot{\mathbf{x}} \\ \dot{\mathbf{y}} \end{bmatrix} \tag{2}$$

5. Friction: The friction force is generated in the opposite direction of the grip velocity vector. The magnitude of the force is constant. The friction force Ff is given as shown in (3). The gain is Kf.

$$\mathbf{F\_{f}} = \begin{bmatrix} \mathbf{F\_{fx}} \\ \mathbf{F\_{fy}} \end{bmatrix} = \mathbf{K\_{f}} \begin{bmatrix} \dot{\mathbf{x}} \\ \ddot{\mathbf{x}} \dot{\mathbf{y}} \\ \ddot{\mathbf{y}} \\ \ddot{\mathbf{y}} \end{bmatrix} \tag{3}$$

6. Special effect: The special effect force Fe is generated especially in game programs (e.g., the contact force of the pieces of the puzzle and the reaction force when hitting some object).

Therefore, the total haptic force on grip F is the sum of the above six forces, as shown in (4).

$$\mathbf{F} = \mathbf{F\_l} + \mathbf{F\_a} + \mathbf{F\_s} + \mathbf{F\_v} + \mathbf{F\_f} + \mathbf{F\_e} \tag{4}$$

A haptic force other than the above can be generated by easy modification of a program.
