Measuring apparatus using the moire fringe concept of measurement

Abstract

Measuring apparatus using the moire fringe concept of measurement to provide a precise digital numeric indication of displacement between two relatively movable members. The apparatus includes an accurately ruled grating or scale, a transducer head in the form of an index grating supported on a movable carriage and a transducer support housing. The scale is secured in a spar which is preferably mounted to the carriage of a machine tool such as a milling machine. The transducer support housing is mounted to the stationery part or bed of the machine tool and is provided with a cantilever spring element which holds the carriage in direct contact with the scale.

What we claim is: .[.1. Apparatus for measuring displacement between first and second relatively movable members, said apparatus comprising: 
       a. a scale securable to said first member, said scale including first and second adjacent surfaces, said first scale surface being angled with respect to said second scale surface, one of said first and second scale surfaces having a given line frequency; 
       b. transducer means including a carriage and an index grating, said carriage including first and second adjacent scale engaging surfaces, said first scale engaging surface being angled with respect to said second scale engaging surface at substantially the same angle that said first scale surface is angled with respect to said second scale surface, said index grating being held by said carriage parallel to and spaced from said one of said first and second scale engaging surfaces; 
       c. support means securable to said second member; and 
       d. means for continuously maintaining said first scale engaging surface in engagement with said first scale surface and said second scale engaging surface in engagement with said second scale surface, said means for continuously maintaining being secured to one of said transducer means and said support means, said means for continuously maintaining being connected to the other of said transducer means and said support means by means which permit at least limited rotational movement in every direction, said means for continuously maintaining being rigid in a direction parallel to the direction of relative movement between said first and second members and flexible in directions transverse to said direction of movement, whereby in operation when said first member moves relative to said second member the relative spacing and alignment between said index grating and said one of said first and second scale surfaces remains substantially constant..]. .[.2. The apparatus as set forth in claim 1 further including spar means, said spar means holding said scale and having a mounting surface engageable with said first member..]. .[.3. The apparatus as set forth in claim 2 further including a dovetail mounting means for mounting on said first member, said spar being provided with a mating dovetail mounting means whereby said mounting surface may be held in engagement with said first member..]. .[.4. The apparatus as set forth in claim 2 wherein said spar is provided with a longitudinally extending slot which is inclined with respect to said mounting surface, said scale being received in said slot..]. .[.5. The apparatus as set forth in claim 1 wherein said means for continuously maintaining is a spring..]. .[.6. The apparatus as set forth in claim 5 wherein said carriage is provided with a socket, and said spring is secured at one of its ends to said support means and carries a ball on its opposite end which is received in said socket..]. .[.7. The apparatus as set forth in claim 6 wherein said carriage includes light means and photoelectric sensing means..]. .[.8. Apparatus for measuring displacement between first and second relatively movable members, said apparatus comprising: 
       a. a scale, said scale including first and second adjacent surfaces, said first scale surface being angled with respect to said second scale surface, one of said first and second scale surfaces having a given line frequency; 
       b. means for securing said scale to said first member; 
       c. transducer means including a carriage and an index grating, said carriage including first and second scale engaging means, said first scale engaging means adapted to engage said first scale surface, said second scale engaging means adapted to engage said second scale surface, said index grating being held by said carriage such that said index grating is parallel to said one of said first and second scale surfaces when said first scale engaging means is in engagement with said first scale surface and said second scale engaging means is in engagement with said second scale surface; 
       d. support means securable to said second member; and 
       e. force applying means, said force applying means acting on said carriage means to simultaneously hold said first scale engaging means in engagement with said first scale surface and said second scale engaging means in engagement with said second scale surface, said force applying means maintaining the spacing between said carriage and said support means in the direction parallel to the direction of relative movement of said first and second members constant, said force applying means being secured to one of said carriage and said support means, said force applying means being connected to the other of said carriage and said support means by means which permit at least limited rotational movement in every direction, whereby in operation when said first member moves relative to said second member the relative spacing and alignment between said index grating and said scale remains substantially constant..]. .[.9. The apparatus as set forth in claim 8 wherein said first and second scale engaging means are surfaces which are adjacent to each other and angled with respect to each other at the same angle that said first scale surface is angled with respect to said second surface..]. .[.10. The apparatus as set forth in claim 9 wherein said force applying means is a cantilever spring..]. .[.11. The apparatus as set forth in claim 10 wherein said spring is provided with a ball on one of its ends and is secured at its opposite end to said one of said carriage and said support means, and wherein said other of said carriage and said support means is provided with a socket for receiving said ball to form a ball and socket type connection..]. .[.12. A transducer head for riding on a scale, said scale having first and second adjacent surfaces, said first scale surface being angled with respect to said second scale surface, said head comprising: 
       a. carriage means, said carriage including first and second adjacent scale engaging surfaces, said first scale engaging surface being angled with respect to said second scale engaging surface at substantially the same angle that said first scale surface is angled with respect to said second scale surface, one of said first and second scale engaging surfaces being provided with an opening; 
       b. an index grating, said grating being supported in said opening parallel to and spaced from said one of said first and second scale engaging surfaces; 
       c. photoelectric sensor means, said sensor means supported on said carriage in spaced relation to said grating on one side thereof; and 
       d. light means, said light means supported on said carriage in spaced relation to said grating and on the opposite side thereof such that said grating and said one of said first and second scale engaging surfaces lie between said light means and said sensor means..].  .[.13. Apparatus for measuring displacement between first and second relatively movable members, said apparatus comprising: 
       a. a spar, said spar comprising an elongated channel having a generally U-shaped cross-section, the external surface of said channel including a mounting surface, said mounting surface being provided with a dovetail extending the length of said channel, said dovetail being designed to receive a mating dovetail provided on said first member to thereby secure said mounting surface to said first member, the interior of said channel being provided with a longitudinally extending slot, said slot being inclined with respect to the plane of said mounting surface; 
       b. a scale, said scale secured in said slot; 
       c. transducer means including a carriage and an index grating supported on said carriage; and 
       d. means secured between said second member and said carriage for coupling said carriage to said second member whereby, when said first member moves relative to said second member, said carriage moves relative to said scale..]. .Iadd. 14. Apparatus for measuring displacement between first and second relatively movable members, said apparatus comprising: 
       a. a dovetail mounting member securable to said first member; 
       b. a spar, said spar being provided with a dovetail mounting means which cooperates with said dovetail mounting member to secure said spar to said first member; 
       c. a scale secured to said spar, said scale including first and second adjacent surfaces, said first scale surface being angled with respect to said second scale surface, one of said first and second scale surfaces having a given line frequency; 
       d. transducer means including a carriage and an index grating, said carriage including first and second adjacent scale engaging surfaces, said first scale engaging surface being angled with respect to said second scale engaging surface at substantially the same angle that said first scale surface is angled with respect to said second scale surface, said index grating being held by said carriage parallel to and spaced from one of said first and second scale engaging surfaces; 
       e. support means securable to said second member; and 
       f. means for continuously maintaining said first scale engaging surface in engagement with said first scale surface and said second scale engaging surface in engagement with said second scale surface, said means for continuously maintaining being secured to one of said transducer means and said support means, said means for continuously maintaining being connected to the other of said transducer means and said support means by means which permit at least limited rotational movement in every direction, said means for continuously maintaining being rigid in a direction parallel to the direction of relative movement between said first and second members and flexible in directions transverse to said direction of movement, whereby in operation when said first member moves relative to said second member the relative spacing and alignment between said index grating and said one of said first and second scale surfaces remains substantially constant. .Iaddend.