**4. Software for rehabilitation and evaluation**

154 Haptics Rendering and Applications

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

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

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y x

2. Assistance: The assistance force is generated in the same direction as the grip velocity vector. The magnitude of the force increases in proportion to the distance between the current grip position and the target position. The assistance force Fa is the same as the

3. Spring: The spring force is generated in the direction of the initial grip position. The magnitude of the force increases in proportion to the distance between the current position and the initial position of the grip. The spring force Fs is the same as the force

4. Viscosity: The viscosity force is generated in the opposite direction of the grip velocity vector. The magnitude of the force increases in proportion to the velocity of the grip.

 

F F F <sup>v</sup> vy vx <sup>v</sup>

<sup>y</sup>

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

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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).

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

F F F <sup>f</sup> fy fx

f

K

0 0

K

<sup>y</sup>

l

 

<sup>l</sup> (1)

 

> 

> >

 

FFFFFFF efvsal (4)

y y x x

 

(2)

(3)

x K

x

position is (x, y), the target position is (x0, y0) and the gain is K1.

 

F F

ly lx

F

force in (1), except the gain is replaced by Ka.

The viscosity force Fv is shown in (2). The gain is Kv.

in (1), except the gain is replaced by Ks.

(3). The gain is Kf.

**3.2 Haptic force generation** 

force are described as follows.

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 programs.

Fig. 3. Program selection menu
