Patent GB-836673-A (GB)
Title: Improvements in and relating to automatic curve sensing systems
IPC: G05B19/12
Filed: 1958-03-05
Abstract: 836,673. Electric copying-machines. CONTRAVES A.G. March 5, 1958 [March 22, 1957], No. 7057/58. Class 40 (1). Apparatus for following a line on a chart drawn with ink having either a high conductivity or high dielectric constant, comprises a differentialcapacity sensing head normally balanced with the line symmetrically located relative to the two fixed electrodes, and producing an unbalance voltage with relative displacement, which is used to recentralize the head relative to the line. As shown (Figs. 1, 2) the sensing- head 1 has two, symmetrical, triangular-shaped electrodes 11, 12 held in an insulating body 10, and located centrally over a line 4 drawn on a paper chart 3. The electrodes 11, 12 are fed with A.C. from a source G, and a relative movement #Y in the Y direction causes a voltage to appear across the resonant circuit K, which is amplified at SV to drive a motor SM repositioning the head 1 relative to the line 4. An antihunting voltage produced by a tacho-generator TG is added to the error voltage. As shown, the line 4 is of high dielectric constant ink, and a metal rail 2 is located under the line to form the third electrode of the differential capacitor; in a modification the line 4 is drawn in conducting ink and itself forms the third electrode. The sensing-head 1 may have two further electrodes 13, 14 (Fig. 4) which are shaped to produce an error voltage indicative of the angular movement #alpha between the line 4 and the head, and is used to rotate the head relative to the line 4, the angular rotation being indicative of the angle between the tangent at the point on the line 4 being examined and a co-ordinate axis on the chart. In an embodiment (Fig. 6) for use with a copying-machine, a block 34 carrying the sensing head 1<1> is moved along an X axis by a motor MX, along a Y axis by a motor MY, and rotated by a motor Malpha. The position of the head 1<1> relative to a conductive line 4 on a board 40 produces a first error voltage indicative of the angle between the tangent to the line 4 and one of the co-ordinate axes, which is fed to a motor Malpha together with an anti-hunting signal from tachogenerator Ta, whereby the head is rotated until its axis coincides with the normal to the point on line 4 under examination, simultaneously rotating a sine-cosine resolver 37 through the same angle, and a second error voltage indicative of the linear displacement between the centre of the head 1<1> and the line 4, which is fed to the resolver 37 to determine the component displacements along the co-ordinate axes. A constant voltage V representing a desired constant tangential velocity of the head 1<1> is also fed to the resolver 37, whereby the component velocities along the axes are determined, and are combined with the signals representing the component displacements along the axes, and the resultant signals are fed to motors MX, MY together with anti-hunting signals from tacho-generators TX, TY to produce the correct component movements to maintain the head 11 centrally over the line 4, and move it along the line at a constant tangential velocity. The rotations of motors MX, MY, Malpha are transferred by selsyn transmitters SX, SY, Salpha to a copying-machine.