Patent GB-936951-A (GB)
Title: Improvements in or relating to cam devices
Inventor: ROWSTRON GEORGE ORMEROD
IPC: G06K11/02
Filed: 1958-12-09
Abstract: 936,951. Photo-electric cam followers. RANK PRECISION INDUSTRIES Ltd., [trading as TAYLOR, TAYLOR & HOBSON]. Dec. 7, 1959 [Dec. 9, 1958], No. 39603/58. Class 40 (3). An optical cam device comprises a sheet having small discrete circular dots of uniform size contrasting in respect of light transmitting properties with the background constituted by adjacent portions of the sheet, such dots being slightly displaced in turn from one another along a curved path corresponding to the desired cam slope or contour. The optical cam device can be used in a movement control system in which a light-source directs a beam to a small aperture adjacent the line of dots and photoelectric means sensitive to the lateral displacement of the aperture relative to the line of dots controls an arrangement for causing relative movement between the optical device and the small aperture to correct for such lateral displacement and the desired movement is effected in accordance with said correcting movement. The dots may comprise holes punched out of the sheet but preferably the optical cam device is produced photographically, Figs. 2 and 3, as described in Specification 936,952, in which an arcuate photographic plate C is mounted on a slotted and shaped extension B secured to a rotatable disc-A moved by an arm A<SP>2</SP> and a link A<SP>3</SP> from a sector H with a circumferential scale H<SP>1</SP> associated with a fixed mask H<SP>2</SP>. A light spot is formed by a small aperture G in association with an optical assembly comprising lenses E<SP>3</SP>, E<SP>4</SP> and a lamp E<SP>2</SP> mounted in a casing E which is movable radially along guides F by a micrometer screw F<SP>1</SP>. After each radial and rotational setting the actuation of a push-button E<SP>5</SP> operates a shutter E<SP>5</SP> to project a light spot on to the plate C, which is subsequently developed. The negative or derived positive plate C is mounted in apparatus, Figs. 4 and 5, generally similar to that of Figs. 2, 3 but in which the disc A carrying the plate B and optical cam device C is rotated by a motor A<SP>4</SP> through gearing A<SP>5</SP>, A<SP>6</SP>, and a casing K carrying a light source K<SP>1</SP>, lenses K<SP>2</SP> and a plate with an aperture K<SP>3</SP> in association with a beam-splitting prism L and photoelectric cells L<SP>1</SP>, L<SP>2</SP> is moved in one or the other manner in the radial direction by a threaded shaft M<SP>3</SP> driven by a motor M and engaging an arm N pivoted at N<SP>1</SP>, Fig. 4, and secured to a bracket L<SP>3</SP> attached to the casing K. When the cam contour is defined by opaque dots on a transparent background the diameter of the aperture K<SP>3</SP> may be about twice that of the dots, Fig. 6 (not shown), so that when the aperture is correctly positioned relative to the line of dots, the opaque line divides the beam passing through the aperture into two equal portions which are further separated by the prism L. In the converse case of translucent or transparent dots on an opaque background, the aperture K<SP>3</SP> may be of the same size as the aperture G, Fig. 3, used in the photographic production of the cam device and a graticule having an opaque line parallel to the edge of the prism L is mounted on the upper wall of the casing L<SP>3</SP>, Fig. 5, to ensure proper division of the light beam between the two photo-cells. A similar graticule may also be used in the cam of opaque dots on a translucent background when such dots are spaced apart instead of overlapping or when the line of dots has portions steeply inclined to the edge of the prism L. The single beam-splitting prism L, Fig. 5, may be replaced by a pair of prisms X, X<SP>1</SP>, Fig. 8, side-by-side with their inclined reflecting surfaces facing in opposite directions, the plane of the contacting side surfaces of the two prisms constituting the operative " edge " of the beam-splitter, An inclined mirror X<SP>2</SP> may also be used to provide a more compact optical unit. The motor M is controlled as shown in Fig. 7 by a relay T in the output circuit of a thermionic valve P whose grid P<SP>1</SP> is connected to the two photo-electric cells L<SP>1</SP>, L<SP>2</SP> forming with resistors Q<SP>1</SP>, Q<SP>2</SP> a bridge circuit having diagonal arms formed by a resistor Q and the anode-cathode circuit of the valve. When the outputs of the cells L<SP>1</SP>, L<SP>2</SP> are equal, the valve P provides current to operate the relay T which through contact T<SP>1</SP> operates contactor relay U and contacts U<SP>1</SP>, U<SP>2</SP> to operate the motor M in the reverse direction from that corresponding to the released positions as shown, of the contacts U<SP>1</SP>, U<SP>2</SP> so that the motor M oscillates rapidly between its forward and reverse drives. The supply circuits are controlled by a main switch W with contacts W<SP>1</SP>, W<SP>2</SP> for a mains-operated eliminator R and an indicating lamp V<SP>1</SP>, the contact W<SP>4</SP> controlling the circuit for the motor M and contact W<SP>3</SP> controlling the shunt circuit of the relay T. The closure of contacts W<SP>1</SP> also illuminates an indicating lamp V<SP>6</SP>, and the light source K<SP>1</SP> is energized by a transformer V<SP>7</SP> connected to the mains circuit V by a switch V<SP>8</SP>.