Patent GB-1127393-A (GB)
Title: A tracer assembly for a copying tool
IPC: B23Q35/34
Filed: 1966-07-25
Abstract: 1,127,393. Template followers. NASSOVIA. WERKZEUGMASCHINENFABRIK G. m.b. H. July 25, 1966 [July 24, 1965; Aug.7, 1965; Oct. 2, 1965], No.33423/66. Addition to 1,126,959. Heading G3N. [Also in Division B3] A tracer assembly for a copying machine tool comprises a tracer, a control head having a rotary member and a stationary member rigidly mounted on the tracer, the rotary member being rotatable within or around the stationary member about an axis perpendicular to the selected plane in which the tracer is intended to follow a pattern, biasing means urging the stationary member off centre relative to the rotatable member, drive means connected to the rotatable member, and switch means having three positions controlling the drive means for left hand and right hand and null rotation, the switch means taking up one or other of these positions in dependence upon the direction of off centredness of the stationary member relative to the instantaneous direction of feed movement of the tracer, said switch means having a control member mounted on the rotary member for resilient displacement by the stationary member along the direction of the biasing force into two terminal positions and one middle position corresponding to the left hand and right hand and null rotation positions. A tracer 3, 4 in a copy milling machine is mounted by forked levers 2, 2' so as to be displaceable bodily i.e. parallel to its own axis in three co-ordinate directions such displacement being sensed by hydraulic valves 5, 6, 7, and used to effect corresponding feed movements of the tool and tracer. A measuring ball 10 supported from the upper end of the tracer is surrounded by a rotatable pre-control head 14 which supports a pressure member 20 adapted to apply a force to the ball 10 thereby pressing it into an eccentric position relative to the head; the latter is rotatable in order to ensure that the force is applied at some desired angle, e.g. 30 degrees, to the tangent to the tracer at its point of contact with the pattern surface. Diametrically opposite to the pressure member the pre-control head carries a switch having three contact positions which respectively give rise to clockwise rotation, no rotation or anti-clockwise rotation of the head 14 through electrical relay control means and a motor 13. Equispaced from the switch on either side thereof are support rollers 29, 30. When the tracer is moving normally along a straight portion of the pattern surface the ball 10 is in contact with one support roller e.g. 29 and the switch and in this position no rotation of the measuring head occurs. When a change in direction of the pattern surface is encountered the ball may either lose contact with the roller or make contact with both rollers, either condition causing the switch to move to a fresh position to cause rotation of the pre-control head in an appropriate direction to restore the direction of the applied force to its desired angle with the contact tangent and to restore the ball 10 to its normal eccentric position relative to the head 14 in which no rotation of the latter occurs. The pre-control head 14 is supported by housing member 12, 31 which provide for angular adjustment of the head about the tracer axis and about an axis perpendicular thereto, the particular setting of the head determining the scanning plane of the tracer. The switch may be adjusted radially to regulate the angle between the biasing force applied to the tracer and the contact tangent. A reversing switch arrangement is provided so that at the end of each scanning movement the measuring head is adjusted for a scanning operation which is initiated in the reverse direction. In a modification Figs.13, 14 (not shown) the switch bears upon a lever carrying the pressure roller and not directly on the measuring ball. In a further modification Fig. 16 (not shown) the switch is mounted coaxially with the drive motor for the measuring head and is connected by a rod to one end of a cranked lever carrying the pressure roller. In all embodiments a pivotally mounted tracer member may be substituted for the forkedlever-mounted type shown.