GB1210888A - Measuring apparatus coupling - Google Patents

Abstract

1,210,888. Machine tool details. BRITISH AIRCRAFT CORP. Ltd. 10 July, 1969 [26 June, 1968], No. 30480/68. Heading B3B. In measuring apparatus of the type used, e.g. to measure the displacement of a machine tool carriage relative to its bed 1, and which comprises a scale extending along the bed and a measuring head 4 attached to the carriage and having an index co-operating with the scale, the measuring head 4 is connected to the carriage by means permitting relative movement therebetween in directions perpendicular to the direction of measurement and the head is guided to travel at a constant spacing from the scale. The measuring head 4 is guided in a channel 2 one wall of which bears the scale, by rollers 7, 8, 9 and spring loaded sliding pad 11. The drive connection from the carriage to the measuring head comprises a connector block 21 attached to the carriage, an arm 20 projecting into the measuring head and bearing on a rod 25 which at one end has a ball 27 received in conical sockets 24, 26 in the arm 20 and rod 25 respectively, the other end of the rod having a part spherical surface the centre of curvature of which lies at the centre of the ball 27. Thus the rod 25 is adapted to partake of slight movements perpendicular to the scale without altering its effective length. A leaf spring 31 maintains the arm 20 in contact with the rod 25 which is preferably made of a material of very low coefficient of expansion. The measuring device itself comprises a ruled grating 16 disposed beneath a prism 18 at a fixed distance from the scale and photo-electric detectors 19 adapted to indicate the position in dependence upon the formation of Moire fringes. Wiring for the optical system runs from a connector plug 34, 35 in the block 21 through a channel 32 in the arm 20 to the measuring head.