Apparatus for measuring gear

Abstract: A gear measuring apparatus comprises detecting means for outputting detection signals, an X-direction linear travel system for making the detecting means travel linearly in an X direction perpendicular to a radial line and rotation means for rotating the detecting means by causing the X-direction linear travel system to rotate around the rotation center of the gear (100). The gear measuring apparatus further comprises control means for interlocking the rotation and the X-direction linear travel of the detecting means so that a probe draws the standard involute tooth form, because the detecting means, which are set to an initial position, are rotated at only an extremely small angle ϑ by the rotation means, and at the same time the detecting means are made to travel linearly by ϑ·(Dp·cosα)·1/2 with the aid of the X direction liner travel system in the X direction, and recording means for recording the measured results based on detection signals from the detecting means. In addition, Dp is a pitch diameter and α is a pressure angle of the gear (100) to be measured.

Description: The invention relates to a gear measuring apparatus for measuring the profile of the involute tooth form of a gear, said apparatus comprising a - detecting means having a probe for delivering detection signals corresponding to the tooth form of said gear b - rotation means for rotating said detecting means and said gear relative to each other c - a linear travel system for making said detecting means travel linearly in such a way that the probe, contacting a tooth profile of the gear to be measured, would follow a path derived from the mathematically calculated involute tooth form of said gear, if said tooth profile would have the theoretical involute tooth form, said linear travel system being rotatable together with the detecting means d - control means, comprising measuring means to define the actual position of the probe at different points of the path followed thereby, and comparing means to establish the deviations between the measured and the calculated theoretical positions of the probe. A gear measuring apparatus of the above type is known from EP-A-0 131 537. During tooth profile measurements the gear to be measured is rotated. A detecting means is located in front of the gear to be measured, said detecting means being capable of moving in a rotational and translational direction. The rotation (₂) and translation (r₂) of the detecting means are controlled in dependence of the angular movement (₁) of the gear to be measured. The invention has for its object to provide a gear measuring apparatus, particularly for measuring the tooth form of internally toothed large diameter ring gears. According to the invention this object is achieved by providing an apparatus, which is characterized in that e - the rotation means are drivingly connected to the detecting means to make said means rotate relative to the centre of said gear being fixedly mounted, the probe being connected to said detecting means for swivelling movement, f - the linear travel system is connected to said detecting means to make said means travel linearly in a direction perpendicular to a line tangent at the tooth surface to be measured at a point where a radial line connecting the pitch circle and the centre of said gear intersects said tangent line under a pressure angle α, said linear travel system being rotatable around the fixed centre of said gear g - said control means further comprise means for interlocking said rotation means and said linear travel system in such a way that the probe of the detecting means contacting a tooth profile of the gear to be measured would follow a path identical to the standard involute tooth form if said tooth profile would have the theoretical involute tooth form starting from an initial position, causing said detecting means to rotate over an extremely small angle and to travel linearly over a distance ϑ.Dpcosα.1/2, wherein Dp is the pitch diameter of the gear to be measured, with the aid of said linear travel system in said direction and h - recording means for recording the measured results based on detection signals received from said detecting means during the measuring operation, in which said rotation means and said linear travel system are interlocked. With such apparatus the rotation and translation of the detecting means need not to be synchronized with or controlled in dependence of the rotational movement of the gear to be measured. An embodiment of the apparatus according to the invention is described hereinafter with reference to the drawings, in which Fig. 1 (a) is a plan view showing the gear measuring apparatus; Fig. 1 (b) is a front view of the gear measuring apparatus shown in Fig. 1; Fig. 2 (a) is an enlarged front view showing in detail a swing arm attaching portion; Fig. 2 (b) is an enlarged side view illustrating in detail the swing arm attaching portion; Fig. 3 is an enlarged view showing in detail a balance weight; Fig. 4 is a block diagram showing a control system; Fig. 5 is a view explaining the measuring principle; Fig. 6 is a flowchart showing procedures for measuring tooth forms. The measuring principle used for measuring the tooth form according to the present invention wall now be described with reference to FIG. 5. As shown in FIG. 5, numeral 51 indicates an internal gear to be measured, while numeral 12 indicates a detecting means or displacement sensor which rotates around the rotation centre 0 and travels linearly along the X axis. Dimensions of the internal gear to be measured are as follows: Module: M Number of tooth: N Pressure angle: α Pitch diameter: Dp (=M·N) Basic circle diameter: Dg(=Dpcosα) A probe 12a of the displacement sensor 12 is initially set to X coordinate Xg = (Dp·sinα)/2 and Y coordinate Yg = (Dp·cosα)/2 , which constitute the initial values for measuring the gear. The probe 12a is brought into contact with a point on the pitch circle of the tooth surface and the output of the displacement sensor 12 at this moment is set to zero. The pressure angle α is present between a tangent running along said point of the pitch circle of the internal gear 51 and the Y axis (radius line). Under these conditions, the measuring of the gear is started. For example, as shown in FIG. 5, to measure the tooth surface in the bottom direction, the displacement sensor 12 is rotated counterclockwise at only an extremely small angle ϑp and at the same time is made to travel upwardly by only Xp=(Dg/2)·ϑp along the X axis. Since the probe 12a is moved according to the standard involute tooth form, the measured tooth profile has the standard involute tooth form, if the output of the displacement sensor 12 remains zero. If the tooth form deviates from the standard involute tooth form, the sensor 12 delivers detection signals corresponding to the errors. By repeating such operation as described above, that is, repeating the ϑp rotation and the Xp linear travel until the probe 12a reaches the tooth bottom, the actual tooth form of the internal gear 51 is measured on the basis of the magnitude of the detection signals, which are delivered by the displacement sensor 12 at different measuring points. As shown in FIGS. 1 to 4, the gear measuring apparatus for measuring the tooth form of the internal gear 51 having an involute tooth profile without moving the gear comprises detecting means 12 for delivering detection signals corresponding to the tooth form of the gear, an X-direction linear travel system 4 for making the detecting means 12 travel linearly in a X direction, perpendicular to a tangent line which intersects, under the pressure angle α, a straight line connecting a point on the pitch circle and the tooth surface with the centre 0 of the gear 51, and rotation means 3 for rotating the detecting means 12 by causing the X-direction linear travel system 4 to rotate around the rotation centre 0 of the gear 51. The gear measuring apparatus according to the present invention further comprises control means 41 for interlocking the rotation means 3 and the X-direction linear travel system 4 so that a probe 12a moves according to the standard involute tooth form. The control means 41 causes the detecting means 12, which are set to an initial position, to rotate at only an extremely small angle ϑ by the rotation means 3, and at the same time the control means 41 causes the detecting means 12 to travel linearly by only ϑ·(Dp·cosα)·1/2 by means of the X-direction liner travel system 4 in the X direction, which is perpendicular to the tangent line defined above. The gear measuring apparatus further comprises recording means 49 for recording the measured results based on detection signals received from the detecting means 12 during the measuring operation, in which the rotation means 3 and the X-direction linear travel system 4 are interlocked and the interlocking operation is repeated. The detecting means 12 are so rotated and made to travel linearly by the control means 41 as to follow a path corresponding to the standard involute tooth form. During the above motion, the the tooth form measurements are recorded on the recording means 49, which show the signals delivered by the detecting means at different measuring points. The tooth form is thus measured. An apparatus according to the invention will be further described in detail below with reference to FIGS. 1 to 6. As shown in FIGS. 1 (a) and 1 (b), an apparatus 100 for measuring a gear 51 is so arranged on a surface plate 1 as to slide freely. After a position of the apparatus 100 for measuring the gear 51 is set with respect to the rotation centre of an internal spur gear to be measured, which is already fixed on the surface plate 1, measurement is performed. A turn table 3 rests on a base 2 having a large number of air exhaust nozzles on its under-face. The turn table 3 is rotatable in extremely small angles with the aid of a step motor. An X-axis travel system 4 is provided on the turn table 3 and a Y-axis travel system 5 is arranged on an X table 4a of the X-axis travel system 4. The X-axis travel system 4 moves the Y-axis travel system 5 in extremely small increments along the X axis, which runs through the centre of the turn table 3. A Z-axis travel system 6 is arranged at the end of the Y-axis travel system 5 and is capable of moving along the Y axis perpendicular to the X axis. The Z-axis travel system 6 moves a swing arm 8 up and down along the Z-axis with the aid of a bracket 7, which is disposed at the lower end the Z-axis travel system 6. As shown in FIGS. 2 (a) and (b), the swing arm 8 is fitted with a pin 10 running through a V-channel 9, which is fixed to the front of the bracket 7 and is fixed by a nut 11 while contacting the V-channel 9. The axial center of the pin 10 extends in a Y' axial direction running through the centre of the turn table 3 in the X and Y planes. The swing arm 8 can turn 180° symmetrically with respect to the Y' axis to allow an accurate position of the swing arm 8 by the V-channel 9. The front end of the swing arm 8 is bent in the Y axis direction only to the degree corresponding to a pressure angle α of the tooth form. A displacement sensor 12 called an electrical micrometer is attached to the front end of the swing arm 8. The displacement sensor 12 delivers a detection signal corresponding to the displacement of a probe 12a at the tip of the displacement sensor 12, when the probe 12a is pressed against the tooth surface. Denoted 13 is a counterweight to counterbalance various components on the X table 4a. As shown in FIG. 3, the counterweights 13 are so arranged as to slide on rails 14 in the X axis direction. One end CB of each of four cables 15a to 15d is respectively connected to each counterweight 13. The other end CA of each of the cables 15a to 15d is so fitted over pulleys 16a to 16d, which are arranged on the turn table 3, as to be attached to the X table 4a. When various components on the X table 4a move in one direction along the X axis, each counterweight 13 moves in the opposite direction the same distance traveled by the various components in order to counterbalance the Y-axis travel system 5 and other components with respect to the Y axis origin. Numeral 17 in FIG. 1 indicates a counterweight moving along the Y axis to counterbalance the Z-axis travel system 6 and the like. The counterweight 17 is positioned at the back end of the Y-axis travel system 5 and the position thereof is manually adjustable. The counterweight 17 counterbalances the Z-axis travel system 6 and the like with respect to the X axis origin. FIG. 4 is a block diagram showing a control circuit of the apparatus for measuring the gear. Signals from the displacement sensor 12 are delivered through an amplifier 42 to a controller 41 and various data and commands from a keyboard 43 are also put into the controller 41. A ϑ-rotation motor 44 for the turn table 3, an X-axis motor 45 for the X-axis travel system 4, a Y-axis motor 46 for the Y-axis travel system 5 and a Z axis motor 47 for the Z-axis travel system 6 are also connected to the controller 41. When the keyboard 43 produces a command for moving the travel system along the axes, the controller 41 controls each movement of the travel systems. A display 48 and a recorder 49 are further connected to the controller 41 to display or record measurements. Procedures for measuring the tooth form of an internal gear by using an apparatus for measuring the gear as described above will be described with reference to FIG. 5. The internal gear 51 is fixed on the surface plate 1 so that the rotation centre line of the apparatus 100 for measuring the gear 51 coincides with the imaginary rotation centre line of the internal gear 51. At this time air is streaming out of the under-face of the base 2 to move the apparatus 100 for measuring the gear 51 by a slight force, so that adjusting the position of the gear measuring apparatus 100 is easily made. After adjusting the position, with the air jets stopped, the position of the apparatus 100 is fixed by its dead weight. The Z-axis travel system 6 then directs the probe 12a to the substantially centre position of the gear face width. The X-axis travel system 4 and the Y-axis travel system 5 are so adjusted that the probe 12a of the displacement sensor 12 is located at the initial coordinates for measurement Xg, Yg as described above, which are determined by a pitch diameter Dp and a pressure angle α. The turn table 3 is rotated to bring the probe 12a into contact with a point on the pitch circle of the internal gear 51. By rotating the turn table 3, the position of the probe 12a is so changed as to put the displacement sensor 12 substantially at the centre of its measurement range. After the position of the probe 12a is set, the value on the display 48 is set to zero. The above-described operation provides an efficient measurement range for the displacement sensor 12. The keyboard 43 then produces commands to measure the internal gear 51. The measurement commands control the distance traveled by the displacement sensor 12 by means of the X axis motor 45 in the X direction and the amount of rotation of the displacement sensor 12 by the ϑ-rotation motor 44 so that the distance traveled corresponds to the amount of rotation in the way described below. The commands can be generated by depressing the space key of the keyboard 43 or inputting required commands. When the tooth form is measured from a point at the pitch circle to the tooth bottom, the turn table 3 is rotated counterclockwise by the commands from the keyboard 43 only by an extremely small angle ϑp, which has been previously determined, in order to cause the displacement sensor 12 to rotate. At the same time, the X-axis travel system 4 advances the displacement sensor 12 upwardly as shown in FIG. 5 by only the amount of (DG/2)·ϑ . By repeating the above-described interlock operation of the rotation and the linear travel through the commands from the keyboard 43, the probe 12 moves along a path according to the standard involute tooth form based on the dimensions of the gear. During the above procedure, when the tooth form is made without any errors, as compared with the standard involute tooth form, the output of the displacement sensor 12 at different measuring points is zero, while on the contrary, if some errors exist in the tooth form, the displacement sensor 12 produces a detection signal proportional to the errors. For these reasons, when the recorder 49 is actuated to correlate the position of the probe 12a on the tooth surface with the output of the probe 12a, the tooth form of the internal gear 51 can be displayed After the measurement in the direction of the tooth bottom is completed, the measurement in the direction of the tooth tip is started. In this measurement, the displacement sensor 12 is rotated clockwise at only an extremely small angle ϑp as shown in FIG. 5 and is moved downwardly by only an extremely small distance Xp. This operation is also performed by commands from the keyboard 43. The detection signals at various measuring points are read and are recorded on the recorder 49 to show accurately the tooth form from the tooth bottom to the tip of the gear. After the above-described procedure, the nut 11 is loosened to rotate the swing arm 8 at an angle of 180° so that the swing arm 8 is positioned symmetrically in relation to the Y axis of FIG. 5 and then the tooth form of the gear is measured. For the same measuring operation, the probe 12a is then withdrawn from between the two teeth for a while and then the turn table 3 is rotated to insert the probe 12a into a place between another two teeth. By repeating the above-mentioned procedure, the tooth form for the gear teeth can be measured. Furthermore, when the X-axis travel system 4 moves the displacement sensor 12, together with the Y-axis travel system 5 and the Z-axis travel system 6, the cables 15a - 15d move each counterweight 13 in such a way that the counterweight 13 and the X to Z axes travel systems 4 to 6 move in an opposed direction to each other with respect to the Y axis in order to counterbalance the Y-axis travel system 5, the Z-axis travel system 6 and other components on the X table 4a. The position of a counterweight 17 is adjusted in accordance with the coordinate position of the probe 12a so that the displacement sensor 12 is counterbalanced in relation to the Y axis. Therefore, the center of gravity of the apparatus 100 for measuring the gear 51 is set substantially at the centre of the turn table 3 to measure the gear very accurately without an eccentric load. Moreover, the swing arm 8 is only rotated 180° at the center of the Y' axis to measure the tooth form of the right and left tooth surfaces, and thus measuring efficiency is improved. The position of the swing arm 8, that is, the position of the displacement sensor 12, is substantially determined by bringing the slope defined on the swing arm 8 into contact with the V-channel 9. This eliminates measurement errors in the X axis direction as compared with those in the right and left tooth surfaces every time the displacement sensor 12 travels over a great distance in the X axis direction. Setting the length of the swing arm 8 in the X-axis direction to a value close to the Xg value described above allows the X-axis travel system 4 to travel around the center of its travel stroke range. As a result, the travel stroke of the X-axis travel system 4 is minimized, contributing to miniaturizing the gear measuring apparatus. Since the tooth form is measured by making the measuring apparatus travel, while the gear is fixed on the surface plate, a support structure for the internal gear 51 is unnecessary. For this reason, it is possible to miniaturize the apparatus. The procedure for performing completely automatically the interlock operation of the ϑ rotation and the X axis traveling is briefly described with reference to FIG. 6. After the probe 12a of the displacement sensor 12 is set at the initial position (Xg, Yg) and the output of the displacement sensor 12 is set to zero, an automatic tooth form measuring command is delivered from the keyboard 43 to the controller 41 to start a program shown in FIG. 6. The logical sequence needed for the execution of the program decides in step S1 whether or not the sensor 12 output is zero. If the sensor 12 output is not zero, the sequence goes to step S15 to display "Retry initial set" on the display 48 and terminates there. If the sensor 12 output is zero, the sequence goes further to step S2 to rotate the displacement sensor 12 counterclockwise over an extremely small angle ϑp and at the same time to move the sensor 12 upward along the X axis only by Xp = (Dp·cosα/2)·ϑp . The sequence then goes further to step S3 to decide whether or not the probe 12 reaches the tooth bottom. If the probe 12 does not reach the tooth bottom yet, the sequence goes back to step S2 to repeat the same logical step as before. If the probe 12 reaches the tooth bottom, the sequence goes further to step S4 for measuring the gear. In step S4, the displacement sensor 12 is rotated clockwise only at an extremely small angle ϑp and at the same time is moved downward along the X axis only by Xp = (Dp·cosα/2)·ϑp . The logical sequence then goes further to step S5, where the recorder 49 records the output of the displacement sensor 12. The sequence goes to step S6 to decide whether or not the probe 12a reaches the tooth tip. Then, steps S4 and S5 are repeated until the probe 12 reaches the tooth tip. During these steps, because the probe 12a moves based on the motion described in step 4 on the line drawn by the standard involute tooth form, if the output of the displacement sensor 12 is zero, the tooth surface is formed according to the standard involute tooth form. The sensor 12 would output detection signals corresponding to any errors in the tooth form. According to the aforesaid procedures, the interlock operation of the ϑp rotation and the Xp linear travel is repeated from the tooth bottom to the tooth tip so that the tooth form of the internal gear 51 can be measured by the detection signals, these signals being measured at various measuring points and being sent from the displacement sensor 12. In step S6, if it is determined that the probe 12a reaches the tooth tip, the logical sequence goes further to step S7, where the recording is stopped. The sequence then goes further to step S8, where the ϑp rotation and the Xp linear travel are repeated until the probe 12a comes to a point farther away from the tooth tip. The sequence goes to step S9 to decide whether or not the measuring process is finished. If the process is not finished, the sequence goes further to step S10. In step S10, the displacement sensor 12 is rotated counterclockwise (ϑn + 1° ). The sequence then goes further to step S11, where the displacement sensor 12 is rotated clockwise at an extremely small angle ϑp and at the same time is moved upward along the X axis by only Xp=(Dp·cosα/2)·ϑp . The procedure described in step S11 is repeated until the probe 12a reaches a pitch point. Then, the logical sequence goes further to step S12 to decide whether or not the probe 12a has reached the pitch point. If the probe 12a has reached the pitch point, the sequence goes further to step S13 to rotate the displacement sensor 12 further clockwise until the output of the displacement sensor 12 comes to zero. The sequence then goes further to step S14 to decide whether or not the output of the displacement sensor 12 has come to zero. If the output of the displacement sensor 12 has come to zero, the sequence goes back to step S2 to proceed with the same operation as described above for measuring the next tooth surface.

Claims: A gear measuring apparatus for measuring the profile of the involute tooth form of a gear, said apparatus comprising detecting means (12) having a probe (12a) for delivering detection signals corresponding to the tooth form of said gear (51) rotation means (3) for rotating said detecting means (12) and said gear (51) relative to each other a linear travel system (4) for making said detecting means (12) travel linearly in such a way that the probe (12a), contacting a tooth profile of the gear (51) to be measured, would follow a path derived from the mathematically calculated involute tooth form of said gear (51), if said tooth profile would have the theoretical involute tooth form, said linear travel system (4) being rotatable together with the detecting means (12) control means (41), comprising measuring means to define the actual position of the probe (12a) at different points of the path followed thereby, and comparing means to establish the deviations between the measured and the calculated theoretical positions of the probe (12a) characterized in that the rotation means (3) are drivingly connected to the detecting means (12) to make said means rotate relative to the centre (0) of said gear (51) being fixedly mounted, the probe (12a) being connected to said detecting means (12) for swivelling movement, the linear travel system (4) is connected to said detecting means (12) to make said means (12) travel linearly in a direction (X) perpendicular to a line tangent at the tooth surface to be measured at a point (X g , Y g ) where a radial line connecting the pitch circle and the centre (0) of said gear (51) intersects said tangent line under a pressure angle α, said linear travel system (4) being rotatable around the fixed centre of said gear (51) said control means (41) further comprise means for interlocking said rotation means (3) and said linear travel system (4) in such a way that the probe (12a) of the detecting means (12) contacting a tooth profile of the gear (51) to be measured would follow a path identical to the standard involute tooth form if said tooth profile would have the theoretical involute tooth form starting from an initial position (X g , Y g ), causing said detecting means (12) to rotate over an extremely small angle (ϑ) and to travel linearly over a distance ϑ.Dpcosα.1/2 , wherein Dp is the pitch diameter of the gear (51) to be measured, with the aid of said linear travel system (4) in said direction (X) and recording means (49) for recording the measured results based on detection signals received from said detecting means (12) during the measuring operation, in which said rotation means (3) and said linear travel system (4) are interlocked. A gear measuring apparatus according to claim 1, characterized in that said apparatus comprises an air supported turn table (3), the linear travel system (4) being arranged on top of said turn table (3). A gear measuring apparatus according to claim 1, characterized in that said apparatus further comprises a second linear travel system (5) capable of making said detecting means (12) travel in a second direction (Y) perpendicular to said first direction (X). A gear measuring apparatus according to claim 1, characterized in that said first linear travel system (4) comprises a table (4a) supporting said detecting means (12) and drive means (45) for driving said table (4a) in said first direction (X), said apparatus further comprising a counter balance system (13, 15, 16), which makes a counterweight (13) travel in a direction opposite to the travel direction of said table so that the centre of gravity of said table (4a) and the members supported thereon is maintained at a fixed point. A gear measuring apparatus according to claim 1, characterized in that said detecting means (12) are so attached as to be capable of being reversed over 180° symmetrically to said second direction (Y).

Inventors: AOKI HIROYUKI, KUBODERA KEIZOU, TAKEDA TOSHIAKI, AOKI, HIROYUKI, KUBODERA, KEIZOU, TAKEDA, TOSHIAKI
Applicants: HITACHI CONSTRUCTION MACHINERY, HITACHI CONSTRUCTION MACHINERY CO., LTD.
Application year: 1990
Main classification: G01B7
IPC codes: G01B21, G01M13, G01B7