WO2007015271A1 - Système et procédé de mesure de déplacement de précision pour machines industrielles - Google Patents

Système et procédé de mesure de déplacement de précision pour machines industrielles Download PDF

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Publication number
WO2007015271A1
WO2007015271A1 PCT/IT2005/000464 IT2005000464W WO2007015271A1 WO 2007015271 A1 WO2007015271 A1 WO 2007015271A1 IT 2005000464 W IT2005000464 W IT 2005000464W WO 2007015271 A1 WO2007015271 A1 WO 2007015271A1
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WO
WIPO (PCT)
Prior art keywords
ccd
type optical
optical sensor
signals
measure
Prior art date
Application number
PCT/IT2005/000464
Other languages
English (en)
Inventor
Massimo Ippolito
Giuseppe Morfino
Original Assignee
Fidia S.P.A.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Fidia S.P.A. filed Critical Fidia S.P.A.
Priority to PCT/IT2005/000464 priority Critical patent/WO2007015271A1/fr
Publication of WO2007015271A1 publication Critical patent/WO2007015271A1/fr

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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
    • G01B11/002—Measuring arrangements characterised by the use of optical techniques for measuring two or more coordinates

Definitions

  • the present invention refers to a precision measuring system for industrial machines, and to a measuring process that uses such system.
  • the invention allows realising a measuring system (and its related process) through optical sensors that perform a linear transduction on any type of surface, being both plane or cylindrical or ultimately spherical.
  • a measuring system and its related process
  • optical sensors that perform a linear transduction on any type of surface, being both plane or cylindrical or ultimately spherical.
  • Such system and process can be applied in particular, but not exclusively, to industrial machines, such as, for example, numerically controlled machine tools .
  • the present invention will be described herein below as applied to the field of numerically controlled machine tools, but it can find an as-well efficient application in all fields in which it is necessary to perform a linear displacement transduction on any plane, cylindrical or spherical surface.
  • the optical sensors in particular the CCD-type optical sensors, are already widely used in many applications, such as optical mice, scanners, fax machines etc.
  • Such sensors are substantially composed of an array of pixels, each one of which is proportionally sensitive to the light radiation which is incident thereon.
  • this technology is used for photographing and coding the documents that, depending on their symbols, will impress the array of pixels that will thereby generate an image corresponding to the document.
  • this technology is used for photographing the movement surface of the mouse. This occurs with a determined frequency, so that from the comparison between two following photographs, one is able to go back to the performed movement.
  • the precision burden is based on the quality of divisions etched on the ruler and operatively read by the cursor. They must keep a rigidly- determined resolution and linearity when the temperature chances and for the whole length of the working, stroke.
  • CCD-type optical sensors in the industrial field, and in particular in the field of machine tools (particularly milling machines) follows from the very high technical and performance requirements that are necessary in such field; in particular, for measuring the movement of an object in space, such sensors must have: resolution ⁇ 1 ⁇ m (from one micron to one tenth of a micron) ; response time ⁇ 200 ⁇ s .
  • object of the present invention is providing a precision measuring system for industrial machines that is able to measure the spatial position of the tool member according to the above-mentioned requirements.
  • an object of the present invention is providing a measuring process that uses the optical sensors system according to the present invention.
  • FIG. 1 shows a block diagram that schematically shows the system components according to the present invention and the exchanged flows of information
  • FIG. 2A, 2B and 2C schematically show an example of a processing mode of the procedure according to the present invention.
  • FIG. 3 shows an example of a screen generated by a computer program realising the process according to the present invention.
  • the system for linear displacement transduction through optical sensors according to the present invention has been implemented for measuring the position of a moving object, using at least a CCD-type optical sensors, observing its surface roughness, that is intrinsic to the material of which it is composed.
  • the observed object can therefore have a generic surface, though it must be taken into account that some types of material has better characteristics than others.
  • the system 1 for a linear displacement transduction 1 through optical sensors for numerically-controlled machine tools comprises: at least one optical system 20 equipped with at least one CCD-type optical sensor 10 adapted to acquire in time images of an object 40 whose movement amount has to be measured; preferably, and as will be seen below in more detail, in the preferred embodiment of the present invention that is described and shown, the optical system 20 is a digital video-camera equipped with the CCD-type optical sensor 10; means 30 for acquiring, processing and computing the video signals 80 generated by the CCD-type optical sensor 10 for determining the measure signals 90 representing the amount of displacement of the object 40.
  • the optical system 20 comprises, in the preferred embodiment of the present invention, an optical assembly composed of a simple lens without diaphragm whose only task is conveying the light 50 reflected by the object 40 on the CCD-type optical sensor 10 placed on the video- camera bottom. It is however obvious that the optical system 20 can be equipped with a self-focusing system that allows using the system 1 with variable working distances and depending on the type of object 40 to be displayed.
  • the system 1 according to the present invention can also comprise an artificial lighting system 60 of the object 40 to be observed.
  • lighting is one of the most important parameters for operating the system 1 according to the present invention.
  • it can be used as a LED-type lighting system 60 that produces a red-coloured light 70 that is bright and with excellent uniformity.
  • the chosen colour points out the contrasts of the material composing the lighted object 40 providing a video signal 80 which is full of information.
  • the lighting system 60 is composed of a base made of insulating material drilled at its centre (C-mount sizes), in order to be able to be mounted coaxially to the optical assembly.
  • incandescent lamps that can be used in such context have the following inconveniences: a weak lighing intensity, a fluctuation of the luminous level due to the lamp supply frequency, a scarce capability of directing the light towards the object 40 to be displayed, shadow problems on the sides due to a non-uniform lighting on the object 40 itself.
  • the following description will be performed by taking into account this latter one as a linear array sensor, but it is clear that it can also be, as can be seen afterwards, with an array of pixels without departing from the scope of the present invention.
  • the parameters to be taken into account for choosing an appropriate CCD-type optical sensor 10 depending on a specific application are numerous; in particular, the following are major ones: number of pixels; size of pixels; sensitivity; data rate.
  • the number of pixels of a CCD-type optical sensor 10 together with the unit size of the pixels affects the linear size of the CCD-type optical sensor 10 itself. This parameter affects the geometric size of the sensor 10 and the image acquisition time.
  • the pixel size affects the resolution of the system 1; in fact, the smaller it is, the greater is the possibility of reaching high resolutions, however with a lower sensitivity that would require a better lighting. It is possible to also use sensors with rectangular pixels that have the advantage of providing a high sensitivity with a low data rate that slows down the frequency of acquisition of the video signal 80 by the acquiring, processing and computing means 30.
  • the sensitivity of the CCD-type optical sensor 10 points out how every pixel thereof reacts, by producing an electric voltage, to a stress of the luminous type in the unit time.
  • every sensor 10 differently responds when the wavelength of the incident light 50 changes.
  • the data rate is a parameter that expresses the information transfer speed linked to pixel polarisation. This value affects the acquisition speed that consequently affects the total processing time.
  • the optical system 20 of the system 1 according to the present invention has been preferably, but obviously not in a limiting way, equipped with a Toshiba® TCD1209D sensor.
  • the Toshiba® TCD1209D sensor has the following characteristics: number of pixels: 2048; size of pixels [ ⁇ m] : 14 x 14; data rate [MHz] : 20; sensitivity [V/Lx/s] : 31.
  • the acquiring, processing and computing means 30 therefore comprise electronic interfacing means of the CCD-type optical sensor 10; in particular, such electronic interfacing means preferably comprise an electronic printed circuit for conditioning the video signal 80 sent by the CCD-type optical sensor 10; such electronic circuit mainly comprises a first integrated circuit, an integrated amplifier and a second integrated circuit.
  • electronic interfacing means preferably comprise an electronic printed circuit for conditioning the video signal 80 sent by the CCD-type optical sensor 10; such electronic circuit mainly comprises a first integrated circuit, an integrated amplifier and a second integrated circuit.
  • the sensor driving, signal conditioning and amplifying functions have been realised with discrete logics and components, while for reaching the mentioned performance, a migration will have to be performed towards integrated programmable logics.
  • all signals sent to the CCD-type optical sensor 10 are generated, as will be seen afterwards, by the acquiring, processing and computing means 30 through a local computing unit mentioned below, in a complemented way, sent to the first integrated circuit that operates as insulating stage and negates them, and then sent to the CCD-type optical sensor 10.
  • the video signal 80 output by the CCD-type optical sensor 10 is sent to the integrated amplifier, with which darkness is made correspond to low voltage levels and vice versa, then passes through the second integrated circuit, which performs the function of an analogue switch, and finally reaches the local computing unit to be digitised through a 12-bit A/D converter and then transmitted to a remote computing unit of the acquiring, processing and computing means 30 mentioned below.
  • the second integrated circuit is driven by the acquiring, processing and computing means 30 through the local computing unit and operates as switch that opens and closes in such a way as to take the steady-state voltage value for every pixel. In this way, it is avoided that the transient can be confused with real (steady-state) pixel information.
  • the local computing unit is realised by using a development kit C8051F124DK manufactured by company Cygnal based on a 8051 microcontroller.
  • Such device has the advantage of not needing cooling devices when operating.
  • Data transmission from the local computing unit to the remote computing unit occurs in a serial way- converted on USB from the side of the remote computing unit through a USB-Serial converter, to improve the transfer rate that reaches, for example, in the embodiment shown, 921 kbit/s.
  • the remote computing unit acquires data from the local computing unit, preferably on a USB-port, and through a computer program can process the measure signal 90 and display to an operator, through more suitable displaying means 100, the value of the displacement measure of the observed object 40.
  • the remote computing unit is an electronic processor equipped, in particular, with a 2-GHz Intel® Pentium 4 CPU.
  • the system 1 according to the present invention has been mainly described as a monodimensional, fixed-focus system, but it is clear to any skilled person in the art that similar considerations can be made for a system 1 composed of many optical systems 20 which are able to measure three-dimensional displacements of the observed object 40, for example equipped with array CCD-type optical sensors and with acquiring, processing and computing means 30 modified in compliance with the higher number and type of data to be handled, without departing from the scope of the present invention.
  • the measuring process comprises the steps of: cyclically computing at least one correlation value existing between at least two video signals 80 representing video images coming from the optical system 20, and in particular from the CCD-type optical sensor 10, and acquired by the acquiring, processing and computing means 30; from the correlation value, determining a metric displacement value of the observed object 40; generating a measure signal 90 representing the metric displacement value of the observed object 40.
  • the process according to the present invention can provide the step of displaying a numeric measure value representing the measure signal 90.
  • the process according to the present invention can also comprise the steps of: generating synchronism signals for the CCD-type optical sensor 10 in compliance with what is required by the data-sheet of the sensor 10 itself; converting the analogue video signal supplied by the optical system 20 into a digital video signal 80.
  • the step of generating synchronism signals for the CCD-type optical sensor 10 is preferably performed by the local computing unit; the same local computing unit allows performing the step of converting the analogue input video signal with the 12-bit A/D converter for analysing the maximum information contained in the video signal, consequently transmitting 2 bytes per pixel. Since in the above-described example of configuration of the system 1, the transmission of two bytes per pixel (at the speed of 921 kbit per second) slows down the processing flow of the acquiring, processing and computing means 30 (at the system clock rate of 44 MHz) losing the synchronism, a solution has been employed.
  • a first cycle the synchronism signals are generated, the high conversion bytes are transmitted and moreover the low bytes are stored in the RAM memory of the local computing unit.
  • the second cycle the synchronism generation is stopped and then the acquisition is stopped, but all low bytes stored in the previous cycle are transmitted, then the loop is started again beginning from the first cycle.
  • the step of cyclically computing the correlation existing between at least two video images is preferably performed by the remote computing unit; in particular, for computing the correlation, the mathematical cross- correlation function is implemented; if x is a vector of n elements and y a vector of m elements, the cross- correlation between x and y is defined as:
  • the size of the final array must consequently be of at least (n + m -1) elements.
  • Such function actually is used on signals as they come from the CCD-type optical sensor 10 but, preferably, on signals filtered with a high-pass filter with a cutting frequency of 32 kHz. Such action has the effect of removing the low-frequency components, and of leaving all high-frequency signal components unaltered, such components being the richest with information.
  • the result will be a vector whose graph has a maximum placed next to the central vector index.
  • By cross-correlating the reference image with an image related to a following instant in which a displacement occurred there will be a graph with a maximum offset with respect to the centre.
  • Such displacement of the maximum index with respect to the central index of the cross-correlation vector exactly represents the displacement between the two affected images.
  • the minimum resolution that can be obtained when computing the thereby-obtained displacement is therefore one pixel. This means that, having a 1:1 optics, the smallest displacement that could be read is 14 ⁇ m (pixel size of the chosen CCD-type optical sensor 10).
  • the sub-pixelling technique performs a multiplication of the space resolution by exploiting the geometric linearity of the gradual passage of image contrasts between adjacent pixels. By performing a linear interpolation between the numeric value of the cross- correlation vector maximum and the adjacent index value, on the left or on the right depending on the displacement direction.
  • the cross-correlation maximum designated by reference 110
  • the cross-correlation maximum is moving by one pixel on the right as shown in FIG. 2A, 2B and 2C, being the pixels schematically represented by circles and designated by reference 120.
  • FIG. 2A the maximum is perfectly centered and the measure is exact; in FIG. 2B the luminous energy incident on the central pixel is decreasing and is increasing on the right pixel according to a linear law; in FIG. 2C the luminous energy on the central pixel has completely moved to the right adjacent one.
  • the cross- correlation has a distinct and stable maximum; by moving further, the CCD-type optical sensor 10 explores a new portion of space, therefore the points that the new video signal has in common with the reference signal decrease and consequently the whole behaviour of the cross- correlation waveform degrades, making it impossible to measure over the estimated range of 2 mm.
  • the first solution consists in adding 2048 pixels to the starting array, that the sensor obtains and stores by fixing the space in front of it at the beginning, all space increments over the above-mentioned 2-mm limit.
  • the second solution consists in a learning step where the static memory is loaed with the scene pattern with arbitrary length.
  • the invention also refers to a computer .program as defined and contained on a computer-readable medium.
  • a screen generated by the computer program according to the present invention preferably implemented on the remote computing unit, that performs in particular the steps of computing the correlation between images detected by the CCD-type optical sensor 10, determining the metric value of the displacement and displaying such value according to the process of the present invention.
  • the X ⁇ LabWindows/CVI" ver 4.0 development environment from National Instruments has been used.
  • the screen in FIG. 3 preferably shows the following commands and displaying boxes:
  • START ACQUISITION 101 and STOP ACQUISITION 103 allows activating and suspending the connection towards the microprocessor and therefore starting and ending the display of the acquisition lines of the optical system 20.
  • QUIT 105 allows exiting the program.
  • CCD BITMAP 107 shows the numeric value of the acquired signal lines converted into gray tones.
  • CORRELATION / SIGNAL 108 allows choosing the possibility of displaying in the side plotting space 109, the cross-correlation graph or the current signal, coming from the optical system 20 after having been filtered with a high-pass filter.
  • Full Display ON/OFF 111 allows displaying the bitmap on all 2100 signal points or only on a starting signal window, in order to better locate the focusing condition.
  • OPS 113 displays the numeric measure, in millimeters, that is a result of the algorithmic processing; obviously, the numeric measure can also be expressed in other measuring units, such as for example those for anglo-saxon use.
  • the RESET 115 key allows zeroing in order to start a new measure.
  • BROWSE 117 allows recording the acguisition of the optical system 20. It is equipped with functions for selecting the name and path of the file to be recorded and with the RECORD 119 and STOP 121 buttons for starting and stopping the recording.
  • WRONG SYNC 123 shows the number of wrong synchronsation lines when acquisitions tarts.
  • RX LINES 125 shows the number of lines recorded on file, in recording mode.
  • LINE 127 shows the number of lines acquired by the optical system 20 starting from reset in on-line mode.

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

Abstract

La présente invention concerne un système de mesure de précision (1) destiné à des machines industrielles, notamment à des outils de machines à commande numérique et en particulier destiné à capter le déplacement linéaire d’un objet (40), comprenant au moins un système optique (20) muni d’au moins un capteur optique de type CCD (10) conçu pour acquérir des images de l’objet (40) dans le temps, et des moyens d’acquisition, de traitement et de calcul (30) de signaux vidéo (80) générés par le capteur optique (10) afin de fournir des signaux de mesure (90) représentant une quantité de déplacement de l’objet (40). Cette invention concerne également un procédé de mesure utilisant le système (1).
PCT/IT2005/000464 2005-08-02 2005-08-02 Système et procédé de mesure de déplacement de précision pour machines industrielles WO2007015271A1 (fr)

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Application Number Priority Date Filing Date Title
PCT/IT2005/000464 WO2007015271A1 (fr) 2005-08-02 2005-08-02 Système et procédé de mesure de déplacement de précision pour machines industrielles

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PCT/IT2005/000464 WO2007015271A1 (fr) 2005-08-02 2005-08-02 Système et procédé de mesure de déplacement de précision pour machines industrielles

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7763875B2 (en) 2005-09-07 2010-07-27 Romanov Nikolai L System and method for sensing position utilizing an uncalibrated surface

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Publication number Priority date Publication date Assignee Title
SU1259112A1 (ru) * 1985-04-08 1986-09-23 Алтайский политехнический институт им.И.И.Ползунова Устройство дл измерени смещени объекта
DE4234849C1 (de) * 1992-10-15 1994-04-21 Steyr Daimler Puch Ag Optisches Wegmeßsystem
JPH09292215A (ja) * 1996-04-26 1997-11-11 Toyota Motor Corp 変位量計測装置および変位量計測方法
EP0999521A2 (fr) * 1998-11-05 2000-05-10 Tektronix, Inc. Alignement spatial à haute précision, au niveau du sous-pixel, d'images numériques
JP2001235310A (ja) * 2000-02-23 2001-08-31 Railway Technical Res Inst パンタグラフ変位並びに接触力及びトロリ線偏位の測定装置
GB2394543A (en) * 2002-10-25 2004-04-28 Univ Bristol Positional measurement of a feature within an image

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SU1259112A1 (ru) * 1985-04-08 1986-09-23 Алтайский политехнический институт им.И.И.Ползунова Устройство дл измерени смещени объекта
DE4234849C1 (de) * 1992-10-15 1994-04-21 Steyr Daimler Puch Ag Optisches Wegmeßsystem
JPH09292215A (ja) * 1996-04-26 1997-11-11 Toyota Motor Corp 変位量計測装置および変位量計測方法
EP0999521A2 (fr) * 1998-11-05 2000-05-10 Tektronix, Inc. Alignement spatial à haute précision, au niveau du sous-pixel, d'images numériques
JP2001235310A (ja) * 2000-02-23 2001-08-31 Railway Technical Res Inst パンタグラフ変位並びに接触力及びトロリ線偏位の測定装置
GB2394543A (en) * 2002-10-25 2004-04-28 Univ Bristol Positional measurement of a feature within an image

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* Cited by examiner, † Cited by third party
Title
DATABASE WPI Section EI Week 198719, Derwent World Patents Index; Class S02, AN 1987-134715, XP002352176 *
PATENT ABSTRACTS OF JAPAN vol. 1998, no. 03 27 February 1998 (1998-02-27) *
PATENT ABSTRACTS OF JAPAN vol. 2000, no. 25 12 April 2001 (2001-04-12) *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7763875B2 (en) 2005-09-07 2010-07-27 Romanov Nikolai L System and method for sensing position utilizing an uncalibrated surface

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