Patent GB-882721-A (GB)
Title: Improvements in and relating to electro-mechanical curve sensing systems
IPC: B23Q35/126
Filed: 1958-03-05
Abstract: 882,721. Electric transducers, copying machines. CONTRAVES A.G. March 5, 1958 [March 27, 1957], No. 7056/58. Classes 38 (6) and 40(1). An automatic template follower for guiding a machine-tool or cutting torch, has two feelers mounted on a head which may rotate as well as move along the X and Y axes. One feeler, which is ahead of the axis of rotation of the head, controls this rotation so that a datum line of the head remains tangential to the template. The rotation also controls a resolver from which the X and Y axis control signal components are obtained from the positional error signal output of the second feeler, plus a velocity determining reference voltage. Control system.-A cross-head slide 1, Fig. 9, which is movable along X and Y axes by motors MX, MY and lead screws 10X, 10Y carries the feeler head 3, which is rotatable about an axis 2 by a motor Mα. The rotor of a sine-cosine resolver R rotates with the head 3. The head 3 carries the two feelers F<SP>1</SP> and F<SP>1</SP>α which control transducers F, Fα and these produce A.C. signals modulated in phase and amplitude in accordance with the sense and displacement of their associated feelers. The output of transducer Fαis amplified at 9α and used to control the motor Mα so that the head is rotated until the line joining the two feelers is tangential to the template 5. If the feeler F<SP>1</SP> is deflected due to the head 3 not being aligned with the template, its error signal is resolved along the X and Y axes by the resolver R and used to control the motors MX, MY. In addition a feed speed control voltage is tapped off a potential divider 11 and applied through the resolver R to the motors MX, MY to cause the head to move round the template. The output of the feeler F<SP>1</SP>α also acts to reduce the feed speed control voltage, through a modulator 12, so as to reduce the feed speed round sharp corners. Feeler head construction. The head 3, Fig. 1, rotatably mounted on the X, Y cross-slide 1, carries two variable inductance transducers 61, 62 operated through bell-cranks 51, 52 by their respective feelers. (In this view the feelers are directly one behind the other both engaging the edge of the template 5 seen in X-section). One feeler is on the axis of rotation 2, and the other is displaced so as to contact the template ahead of the axis. Each transducer 61 or 62 is connected in an A.C. bridge to provide an output when the core is displaced from a central position. The feelers are stated to be spring-loaded. It is stated that the transducers may alternatively be differential condensers, or potentiometers. In a modification, Fig. 6 (not shown), it is suggested that the axis of operation of the advanced feeler should be at 45 degrees to that of the main feeler so as to deal with re-entrant curves on the template, but no construction is disclosed. In a further modification, Fig. 7, the advanced feeler 54 is bifurcated so as to contact the template 5 both ahead and astern of the main feeler F, so that the head can traverse the template in either direction.