Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/26—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes
  • G01B11/27—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes for testing the alignment of axes
  • G01B11/272—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes for testing the alignment of axes using photoelectric detection means

Definitions

• the present invention relates to an optical position detector, in particular for measuring the
• Optical position detectors are typically used to enable the displacement of an object to be
• Figure 1 shows an example of a conventional optical position detector.
• the system includes a
• target 2 target 2
• target holder 4 target holder 4
• alignment telescope 6 An operator 8 views the target 2 through
• the telescope defines an image line of sight 13 and an object line of
• the target holder 4 holds the target 2 in a precise spatial relationship to the object (not
• the displacement D of the target and hence the object is proportional to the angle ⁇
• Alignment telescopes have been in use for many years and have proven to be a reliable means of
• magnification of the alignment telescopes varies significantly with focus over the
• an optical position detector comprising:
• the target has a pattern of lines defining a
• processing system is arranged to receive an image of the target and determine therefrom the location of the object relative to said optical axis.
• the present invention provides a position detector using a target with a scale whose criticality
• the image processing system can thus compute
• the scaling factor between the measured image size (which may be in units of number of pixels of
• the image sensor and known, real world, image size and use this scaling factor to determine the
• the target is positioned in a known relationship relative to the object.
• the pattern may be a plurality of concentric shapes, and any adjacent pair of shapes can then
• the shapes can be identified uniquely, and the real dimensions can then be known
• the image processing system if the target is on a far away object, the image processing system
• Each shape also defines the fixed point on the target, for example the centre of the concentric
• the shapes preferably comprise circles and the image processing system is arranged to image at
• the image processing system preferably measures an offset between the optical axis and an
• the invention also provides a method of measuring the offset of an object from an optical axis
• magnification is required because the system is self calibrating. Furthermore, the system can
• Figure 1 shows an example of a conventional optical position detector
• Figure 2 shows an example of a control system used in the optical position detector
• Figure 3 shows an optical position detector according to the present invention
• Figure 4 shows a scaled pattern used on a target used in an optical position detector
• Figure 5 shows a table of values used in the optical position detector of the present
• Figure 3 shows an example of an optical position detector for measuring the displacement of an
• the system has a target 18 and an image processing system 20 having an optical axis 16.
• the target 18 and an image processing system 20 having an optical axis 16.
• the image processing system is arranged to
• the target may reflect
• ambient light or it may be transmissive and a light source may then be provided behind the
• the target 18 has a scaled pattern arranged on its surface which faces the optical processing
• Figure 4 shows an example of a scaled pattern used on the target used in the optical position
• the pattern has a number of concentric rings 22
• the diameter of the circular edge of one ring (either a light to
• the image processing system measures the diameters of the
• the ratio of the diameters of the two rings enables the system to detect which of the concentric
• Centroiding software enables the centre of the pattern to be obtained with high accuracy.
• the image of the target is obtained by the image processing system 20, and a measurement
• consecutive circles in the pattern may be detected (e.g. black to white boundary and white to
• pixels from the centre of the camera optical axis (or some other useful datum in the field of view)
• the distance of the target from the imaging system does not matter.
• the distance of the target from the imaging system does not matter.
• pattern for the target could be employed, including for example,
• This system can be used in the alignment of a number of objects where it is required that they are
• the system could be used to arrange a series of elements such as
• the optical axis may for example be defined by aligning the optical system with the first and the
• the target image is projected onto a reflective surface through a
• the reflected image is collected by the telescope and viewed through a beam splitter.
• the displacement of the reflected image which is dependant upon the rotation of the
• reflective surface to the instrument line of sight can then be measured using an appropriate target and processing system.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Length Measuring Devices By Optical Means (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=10865311

Family Applications (1)

Country Status (4)

Cited By (7)

Citations (4)

• 1999
  • 1999-11-26 GB GBGB9928124.8A patent/GB9928124D0/en not_active Ceased
• 2000
  • 2000-11-24 WO PCT/GB2000/004496 patent/WO2001038823A1/en not_active Application Discontinuation
  • 2000-11-24 AU AU15371/01A patent/AU1537101A/en not_active Abandoned
  • 2000-11-24 EP EP00977736A patent/EP1234159A1/de not_active Withdrawn

Patent Citations (4)

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