<p>The lifting mechanism has at least one lever supported on a shaft which is connected with a tension spring. Between the lever (10) and the spring (22) is located a mechanical control device (16,17) that brings about an almost constant lever arm between a pivot point (15) of the spring and the shaft (8) via a rotation angle of the shaft of up to about 100 degrees. The control device is designed as an intermediate lever which is connected with the lever and at a second pivot point with the tension spring.</p>
