System for measuring the longitudinal or angular displacement of a movable component

• US 3,982,106 A
• Filed: 11/10/1975
• Issued: 09/21/1976
• Est. Priority Date: 05/14/1973
• Status: Expired due to Term

• Current Assignee: Dr. Johannes Heidenhain GmbH
• Original Assignee: Contraves AG (Rheinmetall AG)
• Inventors: Stutz, Theo
• Primary Examiner(s): Thesz, Joseph M.
• Application Number:
  US05/630,723
• Time in Patent Office: 316 Days
• Field of Search: 235/92 GC, 235/92 V, 235/92 MP, 235/92 PL, 235/92 DN, 235/92 CC, 250/237 G, 340/347 P
• US Class Current: 377/3
• CPC Class Codes: G01B 5/30 for measuring the deformation in a solid, e.g. mechanical strain gauge
• CPC Class Codes: G01B 7/02 for measuring length, width or thickness G01B7/004, G01B7/12 take precedence
• CPC Class Codes: G01B 7/30 for measuring angles or tapers; for testing the alignment of axes
• CPC Class Codes: H03M 1/308 with additional pattern means for determining the absolute position, e.g. reference marks

Abstract

A system for measuring the longitudinal or angular displacement of a movable component with respect to a reference position, wherein an increment scale track is supported at a scale carrier affixed to the component, and associated therewith are stationary increment-reading means, an increment counter and electrical circuits for counting properly with respect to the direction of motion of the component the algebraic sum of the increment units traversing in front of the increment-reading means. The scale carrier supports at a second scale track parallel to the increment scale track a multiplicity of absolute-value marks, each of which is spaced from the next following mark by a particular spacing characterizing the absolute value of its distance to the reference position, and which spacing is counted in increment units. The measuring system is constructed to determine the characteristic number of increments which have been algebraically counted at the increment counter from the traversing of any absolute-value mark to the traversing of the next following absolute-value mark in front of a mark-reading means, and to derive from such characteristic number the corresponding absolute value of the displacement of the movable component with respect to the reference position. The absolute value associated with a given characteristic number is fixed in an appropriately programmed read-only storage means. The counter state of the increment counter is then set to the correct absolute value as delivered by the read-only storage means.

Claims

1. An apparatus for measuring the longitudinal or angular displacement of a component, comprising a scale carrier adapted to be supported by the component and movable in a predetermined measurement direction, said scale carrier having a first track comprising an increment scale subdivided into equal graduation units, first stationary reading means defining a first reading location for reading the graduation units moving past the reading location, evaluation means in circuit with said first reading means and comprising an increment counter for the continuous storage of the algebraic sum of the graduation units of the increment scale moving past said first reading location and read by said first reading means, the movable scale carrier possessing a second track arranged substantially parallel to the increment scale, said second track containing a multiplicity of absolute value markings, each marking possessing a predetermined spacing from the next following marking, second stationary reading means defining a second reading location for reading the absolute value markings moving past the second reading location, said evaluation means including means for counting each said spacing in graduation units of the increment scale, the spacing of each marking from the next following marking characterizing an absolute value of its spacing from a null position, said evaluation means including a fixedly programmed allocation device, said evaluation means including means for determining the number of graduation units of the increment scale which have been counted sign-correct at the increment counter from the time of throughpassage of any given one of the absolute value markings up to the throughpassage of the next following absolute value marking, said evaluation means further ascertaining for said characteristic spacing value the associated correct absolute value from said fixedly programmed allocation device and correcting any possibly previously incorrect counter state of the increment counter to the correct absolute value.

2. The measuring apparatus as defined in claim 1, wherein said increment scale constitutes a photoelectrically readable increment scale containing at each graduation unit a dark line and a light line of the same width, said absolute value markings being constituted by code combinations of light and dark strips which extend in length over a multiplicity of graduation units of the increment scale, said absolute value markings in conjunction with said second reading means and said evaluation means generating a characteristic marking pulse during passage of a reference center of an absolute value marking through said second reading location and which reference center is aligned with a predetermined graduation unit of the increment scale.

3. The measuring apparatus as defined in claim 1, wherein said means for counting each said spacing of said absolute value markings comprises a counter state storage which can be set to a new counter state by a pulse, a counter state-comparator means operatively connected in circuit between the increment counter and said counter state storage, said counter state-comparator means during a first clock phase, directly after passage of an absolute value marking through said second reading location, transmitting the characterizing spacing value as a sign-correct difference between an earlier state of the increment counter and a new state of the increment counter to an input of said allocation device, and during a second clock phase, prior to counting a further graduation unit, the absolute value associated with the characterizing difference value is simultaneously transmitted to the counter state storage and the increment counter as a new correct counter state.

4. The measuring apparatus as defined in claim 1, wherein said evaluation means includes means enabling the first absolute value marking passing through said second reading location, after placing the measurement apparatus into operation, to set the increment counter to the counter state null, and during a first clock phase the counter state attained upon throughpassage of the next following absolute value marking is transmitted as the characterizing spacing value to an input of the allocation device and during a second clock phase the thus resulting correct absolute value is transmitted back to the increment counter.

5. In a system for measuring the longitudinal or angular displacement of a component movable with respect to a reference position thereof in one of two possible opposite directions, comprising an increment scale track supported substantially lengthwise parallel to said directions at a scale carrier affixed to the component and having an increment scale subdivided into graduation units of equal magnitude, a stationary increment-reading means, in increment-counting means and electrical circuit means for counting properly with respect to the direction of displacement the algebraic sum of the graduation units traversing in front of the increment-reading means, a second scale track supported substantially lengthwise parallel to the increment scale track at the scale carrier and having a multiplicity of absolute-value marks each having a reading location, a stationary mark-reading means having a reading location and electrical circuit means for generating a mark-signal at the traversing of the reading location of a mark in front of the reading location of the mark-reading means, and a reference location at the second scale track is coincident with a location thereof which would traverse in front of the reading location of the mark-reading means if the component would be located at its reference position, the improvement comprising:

said second scale track having the distance between any two next-neighboring marks constituting a characteristic number of graduation units with which there is unambiguously associated a value of the distance between the reading location of a selected one of said two marks and the reference location at the second track.

6. The system as defined in claim 5, wherein the selected one of said two marks is the one mark whose reading location traverses latest in front of the reading location of the mark-reading means in the course of the displacement of the component.

7. The system as defined in claim 5, wherein said characteristic number and said value of the distance are associated with each other according to a predetermined correspondence fixed in an allocation means.