in a horizontal plane together with the armature 55 of an electromagnet 56 moreover the shifting member 54 has a beveling 57 resting against the beveling 52 of the block 53 under the tension of a tension spring 58 between the lever 8 of the stop motor 3 and the pedal 7 there provided a switching device 59 fig1 and 8 to 13 for the electromagnet 56 and the driving motor 46 the switching device 59 is accommodated in a housing 60 which is clamped to a rod 61 by means of a screw 62 the rod 61 carries at its upper end a displaceable connecting piece 64 lockable by means of a clamping screw 63 the connecting piece 64 is connected to the lever 8 fig1 of the stop motor 3 by means of a ball and socket joint 65 to the lower end if the rod 61 is screwed a tubular shifting member 66 fig9 having a bottom and receiving against the tension of a spring 70 a slider 69 provided with two stop pins 67 68 the shifting member 66 is displacably located in a sleeve 71 which is provided at its lower end with a ball and socket joint 72 connected to the pedal 7 inserted in the upper.