In recent years, with the development of micro- and minicomputers, the expense of associated computer peripherals has often outweighed the expense of the CPU itself. This has been especially true with electronic drafting devices. As a result, there have been a number of efforts in this latter area to reduce costs, the particular philosphy being to reduce the number of electromechanical parts required and to rely on as many passive elements as possible. This philsophy has been particularly predominant in the development of pen-holding and pen-changing devices.
An example of these efforts is described in Offenlegungsschrift No. 29 13 690 published on Oct. 10, 1979, entitled PEN CHANGING DEVICE. This prior art device is shown in FIG. 1. It consists of a pen stable 1 where a pen 2 resides when not in use, and a pen holder 4 which holds pen 2 during plotting. Both pen stable 1 and pen holder 4 are equipped with two-sided flexible clamps 3 and 5, respectively, each having a barb-shaped widening at their free ends. When pen 2 is in its home position in pen stable 1, flexible clamp 3 partially surrounds the pen. However, by moving pen holder 4 close to pen stable 1, flexible clamp 5 moves flexible clamp 3 away from pen 2, permitting flexible clamp 5 to clasp pen 2 and snatch it from pen stable 1. Once the snatch has been completed, pen holder 4 is moved away from pen stable 3 and continues to hold pen 2 during plotting.
In the above design, a significant disadvantage is the use of two-sided flexible clamps. This permits side play of the pen 2 in pen holder 4 and reduces the accuracy of the lateral pen 2 in pen holder 4 and reduces the accuracy of the lateral position of the pen relative to the axis of pen motion, i.e., relative to the X-direction. Furthermore, with this design, the pen can only be snatched from one side of pen holder 4.