Design of an ergonomic control lever for wheel loader attachments

3.1.1 Anatomy of the hand
The hand consists of many parts that work together to perform the functions needed for
daily activities, the most visible part being the skin.
The fingers have the second most amounts of touch- and thermo receptors in the human
body. They are very sensitive to touch, temperature, vibration and more. The fingers
themselves do not contain many muscles but are controlled by long tendons that come
from muscles in the hand and forearm (SCOI, 2010). These muscles are divided into
intrinsic and extrinsic muscles, (figure 3.1). The intrinsic are inside the hand while extrinsic
are placed in the forearm and connect to the hand by long tendons. One intrinsic muscle
group is the hyposthenia seen in the image. The muscles in the arm do the large
movements of the hand while intrinsic muscles control side-to-side movements of the
fingers and thumb. This also have the consequence that pain in the forearm muscles are
related to ergonmics of the hands.
3.1.2 Hand function
According to Haslegrave & Pheasant (2006) the hand is complex and designing hand
tools may require many different measurements to be considered when designing tools,
controls or parts for assembly. Theory research of different grips and the movements the
hands are able to perform, give a basis for the work ahead.
Grips
Attempts at defining the large number of actions capable by the hand have not resulted
in a finite number of grips. There are however a few basic definitions: gripping and nongripping
actions such as poking, pressing, stroking etc. Gripping actions create a “closed
kinetic chain” that hold objects in place. The non-gripping actions fall instead in the
“open chain” category. Gripping is divided into two categories: (figure 3.2)
Power grips: objects are held against the palm using the fingers and thumb.
Precision grips: objects are held with the tips or sides of fingers and thumb.
Figure 3.2 Hand grips (Osvalder & Ulfengren 2009)
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