Firm foundation in the main hci principles, the book provides a working

Figure 3.15 Cells and nerves in the skin. (From Proprioception, Intl. Encyclopedia of Rehabilitation, 
http://cirrie.buffalo.edu/encyclopedia/en/article/337.)

---

5 0
H U M A N – C O M P U T E R I N T E R A C T I O N 
nerves in our muscles and joints. For instance, the muscle spindle/
tendon takes the inertial load, and Pacinian/Ruffini/Golgi receptors 
sense the joint movements, pressure, and torque. The activation force 
for the joints is between 0.5 to 2.5 mN [20]. However, we can under-
stand that this range would vary according to the user’s age, gender, 
strength, size, weight, and so forth. Note that haptic devices are both 
input and output devices at the same time. (We briefly discuss this 
issue of haptic input in the next section in the context of human body 
ergonomics.)
The simplest form of a haptic device is a simple electromagnetic 
latch that is often used in game controllers. It generates a sudden 
inertial movement and slowly repositions itself for repeated usage. 
Normally, the user holds on to the device, and inertial forces are deliv-
ered in the direction relative to the game controller. Such a device 
is not appropriate for fast-occurring interaction (e.g., successive gun 
shots) or for displaying a continuously sustained force (e.g., leaning 
against a wall).
More-complicated haptic devices are in the form of a robotic kine-
matic chain, either fixed on the ground or worn on the body. As a kine-
matic chain, such devices offer higher degrees of freedom and finer force 
control (Figure 3.17). For the grounded device, the user interacts with 
the tip of the robotic chain through which a force feedback is delivered. 
The sensors in the joints of the device make it possible to track the tip 
(interaction point) within the three-dimensional (3-D) operating space. 
(a)
(b)
(c)
(d)