MASK ADJUSTMENT MECHANISM

• US 3,728,551 A
• Filed: 05/19/1971
• Issued: 04/17/1973
• Est. Priority Date: 10/22/1969
• Status: Expired due to Term

• Current Assignee: Richard Leonhard Incorporated
• Original Assignee: Irven H. Culver, Ronald C. Sheltra
• Inventors: Culver, Irven H., Sheltra, Ronald C.
• Primary Examiner(s): Stolwein, Walter
• Application Number:
  US05/144,919
• Time in Patent Office: 699 Days
• Field of Search: 33/141R,125R,125A,125M,141.5,129,134A,134R 235/92V,92PS,98A,103,1A 250/231SE,231,237G,219DD,233,239
• US Class Current: 250/231.16
• CPC Class Codes: B23Q 17/22 for indicating or measuring existing or desired position of tool or work B23Q16/005 takes precedence
• CPC Class Codes: G01D 5/3473 Circular or rotary encoders
• CPC Class Codes: G01D 5/36 Forming the light into pulses

Abstract

A distance measuring system is described in which a wheel is frictionally engaged with a surface along which measurements are made. The metering wheel is connected to a shaft which drives a portion of a photoelectric chopper which provides an indication of increments of metering wheel travel. The chopper includes a disk on the shaft with a plurality of windows alternating with opaque areas in a circular path near the periphery of the disk. A mask having an arc of somewhat similar windows is adjacent and spaced a short distance away from the disk. A pair of lights and a pair of photosensors are located on opposite sides of the maskdisk set. Each photosensor detects light passing through a different plurality of windows in the mask and disk and, as the disk rotates, a substantially symmetrical variation in light intensity occurs. A minimum area non-collimated light source is provided and the mask is located nearer the light source than is the disk. A greater number of windows per unit length is provided on the mask than on the disk so that successful chopping of a non-collimated light beam is obtained when the mask and disk are spaced apart. The mask is mounted on a ring movable by an eccentric and constrained to move only angularly about its center and along a direction normal to a chord between the two photosensors. This permits the phase relation between the photosensor inputs to be adjusted readily and with high precision. Precise adjustment of phase relation and proper mask and disk construction permit the chopper to give usable signals at very high slue rates.

Claims

1. Apparatus for adjusting phase relation in a position encoder, said encoder comprising a first array of windows in a circular arc, a second array of windows in a circular arc substantially the same as the first circular arc, means for rotating one array of windows relative to the other array of windows about the center of the arc, means for sensing alignment of one of the first array of windows with one of the second array of windows, means for sensing alignment of another of the first array of windows with another of the second array of windows, the first and second means for sensing being located on separate radii from the center of arc and wherein half of the angle between the radii to the first and second sensing means is less than the complement of the half angle, the apparatus for adjusting the phase relation comprising:

means for translating the center of arc of one array of windows in a first direction normal to a line between the first and second means for sensing; and

means for preventing translation of the center of arc of the translated array of windows in a second direction normal to the first direction, and wherein the means for preventing translation also permits rotation of the translated array of windows about the center of arc of the translated array of windows.

2. Apparatus as defined in claim 1 wherein the means for translating comprises an eccentric cam connected to the first array of windows.

3. Apparatus as defined in claim 2 wherein the means for preventing translation comprises a pair of arcuate surfaces substantially normal to a line parallel to the line between the first and second sensing means and through the center of arc;

and a pair of parallel guide means normal to the line between the surfaces for guiding engagement with the surfaces, the surfaces being connected to one array of windows and the guide means being connected to the other array of windows.

4. An apparatus as defined in claim 2 wherein the means for preventing comprises:

a cam connected to the first array of windows; and

a cam guide connected to the second array of windows, the cam guide comprising a pair of parallel surfaces normal to and intersecting a line through the center of arc and parallel to the line between the first and second sensing means.

5. A distance measuring instrument comprising:

an instrument case;

means for mounting the instrument case on a first body;

a metering wheel mounted for rotary motion within the instrument case, and including a peripheral portion having a known length with a segment of the peripheral portion extending beyond the instrument case for engagement with a second body movable relative to the first body in a direction in the plane of the metering wheel;

a shaft mounted in the instrument case;

motion amplification means interconnecting the metering wheel and the shaft for rotating the shaft in direct response to, and at a higher rate than, the metering wheel;

a visual indicator connected to the shaft for rotation therewith;

a disk mounted on the shaft for rotation therewith, said disk including a plurality of radially extending windows alternating with a plurality of radially extending opaque areas therebetween in a circular array concentric with the disk;

a mask mounted in the instrument case, said mask including a plurality of radially extendiNg windows alternating with a plurality of radially extending opaque areas therebetween, the windows on the mask extending in an arc of the same radius as the circle of windows on the disk and arranged adjacent thereto;

a first non-collimated light source mounted in the instrument case;

a first photodetector mounted in the instrument case, said first light source and said first photodetector being positioned so that light therebetween passes through windows in a first portion of the mask and a first portion of the disk;

a second non-collimated light source mounted in the instrument case; and

a second photodetector mounted in the instrument case, said second light source and second photodetector being mounted so that light therebetween passes through a second portion of windows in the mask and a second portion of windows in the disk, said second portion of windows being angularly displaced from the first portions of windows;

means for translating the center of arc of the mask windows along a diameter extending midway between the first and second portions of windows; and

means for preventing translation of the center of arc of the mask in a direction normal to the direction of translation.

6. A measuring instrument as defined in claim 5 wherein the means for translating comprises:

a pin mounted with its axis normal to the plane of the mask;

an eccentric camming portion on the pin; and

a cam engaging surface connected to the mask and in engagement with the camming portion; and

wherein the means for preventing translation comprises;

a pair of pins fixed to the instrument case on a line through the center of arc of the windows and parallel to a line between the first and second photodetectors; and

a pair of parallel flat guides connected to the mask and normal to the line between the pins and in guiding engagement with the pins.

7. A measuring instrument as defined in claim 5 wherein each of the light sources comprises a heated filament having a greater length than width and wherein the filament is oriented with the greater length normal to the plane of the mask, and wherein the effective center of the filament is spaced from the mask by a distance A;

the disk being on the opposite side of the mask from the light sources and spaced from the mask by a distance B;

the number of windows per unit arc length on the disk being N; and

the number of windows per unit arc length on the mask being M where M N(B/A +

     1).

8. A measuring instrument as defined in claim 5 wherein the means for translating comprises:

an eccentric cam; and

a cam engaging surface connected to the mask and in engagement with the cam; and

wherein the means for preventing translation comprises;

a pair of parallel flat guides on the housing and normal to a line between the first and second photodetectors; and

a circular portion connected to the mask and in guiding engagement with the flat guides.

9. A distance measuring instrument comprising:

an instrument case;

means for mounting the instrument case on a first body;

a metering wheel mounted for rotary motion within the instrument case, and including a peripheral portion having a known length with a segment of the peripheral portion extending beyond the instrument case for engagement with a second body movable relative to the first body in a direction in the plane of the metering wheel;

a shaft mounted in the instrument case;

motion amplification means interconnecting the metering wheel and the shaft for rotating the shaft in direct response to, and at a higher rate than, the metering wheel;

a visual indicator connected to the shaft for rotation therewith;

a disk mounted on the shaft for rotation therewith, said disk including a plurality of radially extending windows alternating with a plurality of radially extending opaque areas therebetween in a circular array concentric with the disk;

a mask mounTed in the instrument case, said mask including a plurality of radially extending windows alternating with a plurality of radially extending opaque areas therebetween, the windows on the mask extending in an arc of the same radius as the circle of windows on the disk and arranged adjacent thereto;

a first non-collimated light source mounted in the instrument case;

a first photodetector mounted in the instrument case, said first light source and said first photodetector being positioned so that light therebetween passes through windows in a first portion of the mask and a first portion of the disk;

a second non-collimated light source mounted in the instrument case; and

a second photodetector mounted in the instrument case, said second light source and second photodetector being mounted so that light therebetween passes through a second portion of windows in the mask and a second portion of windows in the disk, said second portion of windows being angularly displaced from the first portions of windows;

the number of windows per unit arc length nearer the light sources being greater than the number of windows per unit arc length nearer the photodiodes.

10. A measuring instrument as defined in claim 9 wherein the width of windows nearer the photodiodes equals the width of opaque areas nearer the photodiodes;

and the width of windows nearer the light sources being relatively less than the width of opaque areas nearer the light sources.

11. A photoelectric chopper comprising:

a first mask having an array of windows in a circular arc;

a second mask having an array of windows in a circular arc; and

means for adjusting the relative positions of the first and second masks, said means for adjusting comprising;

a circular portion on the first mask and centered on the center of arc of the windows on the first mask;

a pair of parallel confining walls in engagement with the circular portion of the first mask;

an eccentric cam in engagement with the first mask for translating the mask in a direction parallel to the confining walls and rotating the mask about the center of arc of the windows and means for sensing the alignment of the array of windows in the first mask with the array of windows in the second mask.