Patent GB-974647-A (GB)
Title: Machine tool
IPC: B23B21/00
Filed: 1962-09-18
Abstract: 974,647. Lathes; cutting tools. HEALD MACHINE CO. Sept. 18, 1962 [Nov. 1, 1961], No. 35528/62. Headings B3B and B3T. [Also in Divisions G1, H2 and H4] General.-In a machine tool, Fig. 8, more particularly a lathe, in which a tool 24 having a circular cutting edge 69 is attached to a holder 13 arranged to impart movements in two orthogonal directions, as an essential preliminary to automatic control of the tool position by means of a system 15 incorporating perforated tape or other control media, the tool is first located in a reference position in relation to other elements of the machine with the aid of a control system including a pair of photoelectric cells which defines two in-  spection areas B and D with respect to which the tool must be symmetrically placed and into a projection of which the tool must intrude to a predetermined extent. Departure of the tool from the correct position causes the cell signals to operate via circuits 109 and 112 to actuate relays 225 and 231 which energize in the appropriate direction reversible D.C. motors 204 and 207 whereby slide tables 203 and 206 forming part of the tool holders are moved until the tool is correctly positioned. The motors are energized from positive or negative supplies 219 and 221, relay 225 which controls lateral movement being connected to respond to the difference of the outputs of circuits 109 and 112 and closing contactor 226 or contactor 227 depending on the polarity of the difference, and relay 231 which controls the longitudinal movement being connected to respond to the sum of the outputs of circuits 109 and 112 and closing contacts 231 when the sum is above a predetermined value corresponding to the correct extent of intrusion and closing contactor 233 when the sum is below the value. The automatic control system 15 moves the tool by means of hydraulic actuators 198 and 201 which act on further slide tables 197 and 199. The workpeice 16 to be machined is carried by a head 12 and rotated by a motor (not shown). Checking shape of tool cutting edge.-To check that the tool edge is part of a perfect circle the tool is mounted on a platen 208 which is pivoted on a pin 212 at the centre of the circle and which is normally locked in the correct angular position by wing nut 213. By loosening the nut and rotating the platen, any departure from correct shape or any minor defect in the cutting edge, causes the extent of the tool intrusions in the areas B and D to vary and gives rise to variations in the outputs of circuits 109 and 112. To permit the variations to be detected meters 71 and 74 are provided. Photo-electric cell system. Figs. 5 and 6.-Light from a source 36 passing through apertures 37 and 42 and lens system 45 is collimated by a lens 53 and projected transversely across a chamber 57 into which the tool is introduced. Light passing the tool impinges on a pair of mirror surfaces 67 and 68 and is thereby directed to photo-electric cells B and D. Slits 55 (see Fig. 6) and 61 constrain the light path and cooperate with the edge 69 between mirrors 67 and 68 to define the two inspection areas. Reference photo-electric cells B and C receive light directly from sources 36, the amount of light reaching each cell being adjustable by set-screws 51 and 49. Control system (Fig. 7, not shown).-Each of cells B and D is connected with a reference cell A and C to form a bridge circuit which is energized by a 3.5 kc/s. signal. Each bridge is arranged to be balanced when cells B and D are illuminated with the amount corresponding to correct tool intrusion into the inspection areas, provision being made of switch means whereby the bridges may be balanced with tools of a number of different sizes. Unbalance currents from the bridges are amplified and applied to phase and amplitude responsive detectors which produce output signals which indicate by their amplitude and polarity the extent and direction respectively of the unbalance. These signals are the signals which are applied to relays 225 and 231 and are displayed on meters 71 and 74, Fig. 8. The system, which uses transistors throughout and is energized from a voltage regulated supply, employs conventional circuits.