Patent ID: 7785241

Claim:
A device for obtaining a predetermined linear force, comprising: a first elastic force means; a first force output means comprising a non-elastic, flexible elongated member; a force transformation means arranged between said first elastic force means and the first force output means, pulling the first force output means creates a tension in said first elastic force means, wherein the force transformation means is structured and arranged so that a first pulling force required on the first force output means decreases with a pulling distance that the first force output means is pulled, a second elastic force means; a second force output means attached to said second elastic force means, wherein a second pulling force required on the second force output means increases with the pulling distance the second force output means is pulled, the first and second force output means are connected to each other to sum the first and second pulling forces as a resultant pulling force, characteristics of the first and second elastic force means are chosen so that the resultant pulling force is substantially constant during the pulling distance, and means for adjusting the resultant pulling force from substantially zero and upwards.