Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
  • G01B7/28—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring contours or curvatures
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
  • G01B7/34—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring roughness or irregularity of surfaces
  • G01B7/345—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring roughness or irregularity of surfaces for measuring evenness

Definitions

• the present invention relates to straightness measuring devices, in particular for measuring the straightness of a rail at its weld.
• FIG. 1 very schematically represents a conventional device for measuring rail straightness.
• This is a device known as the GEISMAR rule.
• This device includes a chassis, not shown, provided with two feet 10 which are placed on a rail 12.
• a toothed belt 14 is stretched between two pulleys 16 and 17 parallel to the rails 12.
• One of the pulleys, 16, is provided with a crank 16 -1 allowing to drive, parallel to the rails 12, a carriage 18 fixed to the belt 14.
• the carriage 18 is guided by slides, not shown, which must be manufactured with great care because their straightness must be particularly precise.
• the carriage 18 is provided with a probe 18-1 urged elastically towards the rail 12.
• a probe 18-1 urged elastically towards the rail 12.
• an operator actuates the crank 16-1 to move the carriage 18 from one pulley to the other.
• a stylus not shown, actuated by the probe 18-1 via a link system, traces the profile of the rail on a strip of unrolled paper while the carriage 18 moves.
• a first drawback of this device is that it is particularly heavy (it takes at least two people to transport it) because, to guarantee suitable precision, it is rigid in construction, which requires the use of massive steel parts.
• Another object of the present invention is to provide such a device which is particularly practical to use.
• a device for measuring the straightness of a conductive object comprising a plurality of non-contact distance sensors aligned along an axis of a ruler to be placed on the object, and means of communication of the measurements provided by each sensor.
• the sensors are capacitive sensors.
• the rule comprises at each end a shim to be placed on the object, at least one of which is conductive and provides the object with an electrical signal necessary for the operation of the capacitive sensors.
• the capacitive sensors are produced on rectangular printed circuits comprising on a face opposite to that where the sensors are made of surface-mount electronic circuits intended to process the signals from the sensors.
• the device comprises means for displaying in a coordinate system the amplitudes of the measurements supplied by the sensors as a function of the respective positions of the sensors.
• said object is a rail.
• each end of the rule is removably attached to a block which includes jaws intended to clamp the rail while aligning the axis of the sensors on the axis of the rail, means being further provided for, once the blocks are fixed on the rail, reposition the ruler laterally so as to be able to measure the straightness of a side of the rail at a predetermined position.
• the capacitive sensors are formed by the central part of aligned rings engraved on a layer of copper on the printed circuits, the copper remaining outside the rings playing the role of guard rings. .
• the printed circuits are held in two internal internal grooves of a U-shaped portion of the rule, one of the sides of each groove being straight and serving as a support for the printed circuits. and the other of the sides of each groove being inclined so as to come into contact with the printed circuit without the latter reaching the bottom of the groove.
• Clamping means are provided to bring the two flanks closer to the "U" portion.
• FIG. 1, previously described, represents a positive device. conventional portable rail straightness measurement
• FIG. 2 represents an embodiment of a portable device for measuring the straightness of a conductive object according to the present invention
• FIG. 3 schematically represents an architecture of an information processing circuit supplied by distance sensors used in the device according to the invention
• FIG. 4 represents capacitive distance sensors produced on printed circuit
• 5 shows a rule for maintaining a set of printed circuits of the type of that of Figure 4;
• FIG. 1 previously described, represents a positive device. conventional portable rail straightness measurement
• FIG. 2 represents an embodiment of a portable device for measuring the straightness of a conductive object according to the present invention
• FIG. 3 schematically represents an architecture of an information processing circuit supplied by distance sensors used in the device according to the invention
• FIG. 4 represents capacitive distance sensors produced on printed circuit
• 5 shows a rule for maintaining a set of printed circuits of the type of that of Figure 4
• FIG. 1 represents a positive device. conventional portable rail straightness measurement
• FIG. 2 represents an embodiment
• FIG. 6 represents an external perspective view of an embodiment of a measuring device according to the invention
• Figure 7 shows a sectional view of the device of Figure 6 placed on a rail, a second position of an element of the device being shown in dotted lines.
• FIG. 2 schematically represents a device for measuring straightness according to the invention placed above a weld 12-1 of a rail 12.
• This device comprises an elongated part 20, hereinafter rule, provided on its underside a plurality of non-contact distance sensors 22, for example inductive or capacitive, aligned along an axis corresponding to the axis along which the straightness is to be measured.
• Contactless sensors can be used thanks to the fact that the rail 12 is electrically conductive.
• the measuring device further comprises a housing
• the display 24 provided with a screen 24-1 making it possible to display, thanks to the electronic circuits described later, the measurements provided by each of the sensors 22.
• the display takes place in a coordinate system where the the values of the measurements are represented as a function of the positions of the corresponding sensors.
• the difference between sensors 22 is constant according to one embodiment. It could also be variable in other embodiments; it is possible to have more sensors per unit of length in the center of the rule 20 in order to raise the profile of the rail more precisely at the level of the weld 12-1.
• the coordinate axis assigned to the positions of the sensors is then graduated accordingly on display 24-1.
• the rule 20 is provided at each end with a wedge 26 to be placed on the rail 12.
• These wedges are made of a hard material, for example metal carbide, to minimize their wear during the many uses of the device.
• Such a measuring device is particularly easy to produce because it is not necessary to position the sensors 22 with great precision, in particular perpendicular to the rail 12.
• the sensors 22 are managed by a microprocessor (which is the easiest way to do this) which, on request, runs a calibration program to store values of correction for each sensor 22.
• a microprocessor which is the easiest way to do this
• the positions of the sensors 22 have been modified following a shock, for example, it suffices to rerun the calibration program.
• the measuring device according to the invention does not have heavy parts.
• a measuring device is particularly light and portable by a single person (for a measuring length of approximately 1 m, the device weighs approximately 8 kg).
• a device according to the invention is particularly practical to use since the micr ⁇ prO ⁇ esseur performs most of the measurement steps. The user only has to press a button to view the rail profile.
• FIG. 3 schematically represents an embodiment of the architecture of the sensor management circuit 22 of the capacitive type.
• capacitive sensors are chosen because they make it possible to provide an amplitude signal proportional to the distance measured.
• the same elements as in FIG. 2 are designated by the same references.
• Each sensor 22 consists of a metal plate surrounded by a guard ring 22-1 which is connected to a reference potential. The plates 22 are arranged close to and parallel to the rail 12 to be measured.
• Each plate 22 is connected to a terminal with an adjustable capacity C and to the input of a differential amplifier 28, another input of which is connected to the guard ring. Capacities C are adjusted once and for all during manufacture.
• the outputs of the amplifiers 28 are supplied to an analog multiplexer 30 which switches only one of the outputs of these amplifiers 28 to the input of an amplifier 32.
• the multiplexer 30 is controlled by a microprocessor 34.
• the output of the amplifier 32 is supplied to a demodulator 36, another input of which receives a sinusoidal signal supplied by a generator 38.
• the output of the demodulator 36 is supplied to a filter 40 which supplies a practically continuous voltage Vd corresponding to the distance measured by the sensor 22 selected by the multiplexer 30.
• the voltage Vd is applied to a modulator 42 whose other input receives the sinusoidal signal supplied by the generator 38.
• the generator 38 also supplies the adjustable capacitors C.
• the rail 12 receives the output of the demodulator 42 , which is connected to one of the shims 26 on which the measuring device is placed.
• one aspect of the invention is to group the amplifier 32, the demodulator 36, the generator 38, the filter 40 and the modulator 42 for all of the sensors 22 which may be in high number. These elements being grouped together being the most costly in a capacitive measurement system, significant savings are made.
• the output Vd of the filter 40 is supplied to an analog / digital converter 44 connected to the central unit 34.
• the microprocessor 34 is further associated with a memory 46 (ROM ROM and RAM), with a keyboard 48 and in the above-mentioned screen 24-1, which is for example a liquid crystal matrix display.
• a user presses a specific key on the keyboard 48.
• a program stored in ROM memory, is then executed by the microprocessor 34.
• This program successively selects the sensors 22, reads the corresponding Vd values supplied by the converter 44, and stores these values in RAM memory. Then, or simultaneously, the values read are corrected by values stored in a non-volatile memory, for example during a calibration step, and displayed adequately on the screen 24-1.
• the measured values can be displayed in a coordinate system as a function of the relative positions of the respective sensors, which directly gives the profile of the measured rail.
• the microprocessor 34 can also perform numerous operations on the stored values, for example smoothing or any other operation deemed useful.
• a calibration therefore consists in memorizing the values A and B for each sensor. To do this, we proceed as follows.
• a first calibration phase is carried out with the rule placed directly on a conductive reference plane.
• This plane can be a steel plate of precise flatness.
• the reference plane is a body of water whose flatness has the advantage of being perfect. It is possible, according to the invention, to use a water body as a reference plane because the sensors are non-contact, that is to say that they do not disturb the surface of the water which stays perfectly flat.
• the wedges 26 are then placed on metal pillars which bathe in the water. The user then selects, by pressing a specific key, this first calibration phase.
• the microprocessor performs a first series of measurements by measuring the voltages Vd for each sensor 22, these voltages Vd corresponding to distances d assumed to be zero.
• a second calibration phase is then carried out which consists in placing the rule on the reference plane by placing reference blocks of known height between the reference plane and the blocks 26.
• the user selects the second calibration phase which consists in carrying out a second series of measurements by memorizing the voltages Vd, which then correspond to distances d equal to the height of the reference blocks.
• Vd voltages
• the microprocessor calculates and stores the coefficients A and B for each sensor.
• FIG. 4 represents an embodiment of a set of sensors 22. These sensors are produced on one face of a rectangular printed circuit 50.
• the sensors 22 are formed by etching in the copper layer of one of the faces of the printed circuit of the rings whose internal zones constitute the sensors 22. The remaining copper surface constitutes the set of guard rings 22-1.
• FIG. 5 represents an embodiment of a measurement rule according to the invention, that is to say the part serving as support for the sensor 22. This rule is formed from a profile comprising a part 20-0 to inverted "U" section.
• One or more printed circuits 50 of the type of FIG. 4 are slid into internal grooves 20-1 of the sides of the U-shaped part, near the lower part.
• each groove 20-1 is horizontal and serves as a reference surface and as a support for the printed circuit 50.
• the other side of the grooves 20-1 is inclined so that the printed circuit 50 is supported on the two sides of the grooves without however reaching the bottoms of the grooves.
• Screws 52 distributed over the length of the rule, pass through one of the sides of the U-shaped part and are screwed into the other side. By tightening these screws 52, the two sides of the U-shaped part approach and jam the printed circuit 50 in the grooves 20-1, the inclined sides of these grooves press the printed circuit 50 on the reference plane formed by the right sides of the grooves.
• it includes an ascending part 20-2 so that the rule has a section in "h". This ascending part may have a folded end, as shown, which is used to fix elements such as printed circuits.
• the printed circuit 50 is provided, on its internal face, with components mounted on the surface 54, such as, for example, the amplifiers 28 and the capacitors C of FIG. 3. To perform rail straightness measurements, it is advisable to choose a rule about a meter long. Since it is diffi ⁇ cult to produce printed circuits of such a dimension, the printed circuit 50 is subdivided into, for example, five printed circuits 20 cm long. Each printed circuit 50 is provided with a surface-mounted connector making it possible to connect the outputs of the amplifiers 28 and the common connection of the capacitors C to a printed circuit, not shown, comprising the other elements of FIG. 3. The connectors of the printed circuits 50 are accessible through openings 20-3 made in the U-shaped part 20-0.
• FIG. 6 represents a perspective view of an external embodiment of the straightness measuring device according to the invention.
• the housing 24 of this device is generally elongated parailITApi conclusionsdique.
• Handles 62 are provided in three lateral recesses of the housing 24, one recess being located at the central part and the other two at the end parts.
• the screen 24-1 mentioned above is arranged between an extreme recess and the central recess, and the keyboard 48 is arranged between the central recess and the other extreme recess.
• Each end of the device is provided with a removable fixing block 64 including a quick mounting system on a rail or other profile.
• the housing 24 has an inverted "U" section closed at its lower part by a plate 65.
• the rule 20 is fixed by its longer part on a side of the housing 60, on the side opposite to the handle 62.
• the shims d 'support 26, only one of which is visible in Figure 7, are fixed at the respective ends of the rule 20.
• the wedges 26 are supported on a rail 12 and are electrically isolated from the rest of the device because one of they or both, as mentioned above, transmit an electrical signal to the rail 12 used to perform the distance measurements.
• the block 64 comprises, below the rule 20, a housing for the rail 12 provided with jaws 66. These jaws 66 allow, using a mechanical or hydraulic control, not shown, to tighten the rail 12 for fixing the device on the rail while centering the rule 20 on the axis of the rail in order to carry out a measurement at the appropriate place.
• the blocks 64 are removable. By actuating a mechanical control, the housing 24 of the measuring device can be detached from the blocks 64 which remain fixed on the rail. This possibility is provided so that the housing 24 can be repositioned according to the dotted representation to perform a straightness measurement of the side of the rail 12.
• the end of the housing 24 includes a groove 24-2 provided for sliding on a lug 64-1 of the block 64 and maintain the housing 24 in an adequate position.
• the straightness measuring device according to the present invention has been described in the context of the straightness measurement of rails. Of course, the invention applies to the measurement of straightness of any conductive object, even in a bad conductive material, such as water, graphite ...

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
• Length Measuring Devices With Unspecified Measuring Means (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=9447180

Family Applications (1)

Country Status (7)

Families Citing this family (16)

Family Cites Families (12)

• 1993
  • 1993-05-10 FR FR9305887A patent/FR2705145B1/fr not_active Expired - Fee Related
• 1994
  • 1994-05-09 HU HU9500025A patent/HUT71145A/hu unknown
  • 1994-05-09 EP EP94915602A patent/EP0649512A1/de not_active Withdrawn
  • 1994-05-09 JP JP6525056A patent/JPH08503777A/ja active Pending
  • 1994-05-09 KR KR1019950700084A patent/KR950702701A/ko not_active Application Discontinuation
  • 1994-05-09 US US08/362,576 patent/US5519944A/en not_active Expired - Fee Related
  • 1994-05-09 WO PCT/FR1994/000546 patent/WO1994027114A1/fr not_active Application Discontinuation

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events