JP6420639B2 - Tread shape measurement method - Google Patents

Description

  The present invention relates to a tread shape measuring method for measuring a tread surface shape of a tire using a laser displacement meter.

  Conventionally, an apparatus for measuring the tread surface shape of a tire has been proposed in, for example, Patent Document 1 below. However, this apparatus is limited to static measurement of a part of the tire, and the tread surface shape cannot be measured over the entire circumference of the tire.

JP 2006-153555 A

  One of the required characteristics of tires is steering stability when mounted on a vehicle, and it is understood that the correlation between the steering stability and the tread radius is high. However, the tread radius slightly changes at each position in the circumferential direction due to the tire expansion due to the internal pressure. For this reason, the conventional apparatus cannot measure the tread radius of the entire tire.

  In view of such a situation, the present inventors use a plurality of laser displacement meters to determine the distance in the tire radial direction between each laser displacement meter and the tread surface of the tire rotating around the tire axis around the tire circumference. It was proposed that the tread radius be determined based on the measured data. According to this, since the measured data includes an element of the RRO (radial run out) of the tire, it has been found that a tread radius having a higher correlation with steering stability can be obtained.

  As described above, when the tread surface shape is measured using a plurality of laser displacement meters, the optical axis of each laser displacement meter needs to be appropriately adjusted in order to obtain sufficient measurement accuracy. However, a technique for easily and accurately adjusting the optical axis of each laser displacement meter has not been established, and a proposal for a new technique has been expected.

  The present invention has been devised in view of the actual situation as described above, and provides a tread shape measurement method that can easily and accurately adjust the optical axes of a plurality of laser displacement meters and increase measurement accuracy. The main purpose.

  The present invention is a tread shape measurement method for measuring the tread surface shape of a tire using a plurality of laser displacement meters arranged at intervals in the tire axial direction, and a calibration step for calibrating each laser displacement meter; A measurement step of measuring a distance in the tire radial direction from each laser displacement meter calibrated in the calibration step to the tread surface, and a calculation step of calculating a tread surface shape based on the distance measured in the measurement step. The calibration step includes an optical axis adjustment step of adjusting optical axes of the laser displacement meters in parallel with each other in a plane including the tire axis and perpendicular to the tire axis.

  In the tread shape measurement method according to the present invention, the optical axis adjustment step moves a calibration plate having an irradiation surface irradiated with laser light emitted from each laser displacement meter in the tire radial direction along the plane. It is desirable to adjust the optical axis of each laser displacement meter based on the amount of deviation of the irradiation position of the laser beam on the irradiation surface.

  In the tread shape measuring method according to the present invention, in the optical axis adjustment step, when the moving distance of the calibration plate is 10 to 30% of the outer diameter of the tire to be measured, the deviation amount is 2 mm or less. It is desirable to adjust the optical axis of each laser displacement meter.

  In the tread shape measuring method according to the present invention, it is preferable that the irradiation surface is made of a material containing rubber.

  In the tread shape measurement method according to the present invention, it is preferable that the calibration step further includes an origin adjustment step of adjusting the origin of each laser displacement meter whose optical axis is adjusted in the optical axis adjustment step.

  In the tread shape measuring method according to the present invention, the origin adjustment step is performed on the first reflector that is separated from the axis of the support shaft by a known distance F1 in the radial direction at the base portion supported by the support shaft of the tire. It is desirable to carry out by emitting laser light from each laser displacement meter.

  The tread shape measuring method according to the present invention preferably further includes a gain adjustment step of adjusting a gain of each laser displacement meter whose origin is adjusted in the origin adjustment step.

  In the tread shape measuring method according to the present invention, the gain adjustment step may be performed by applying laser light from each laser displacement meter to a second reflecting plate that is separated from the first reflecting plate by a known distance F2 radially inward or outward. Is preferably performed by emitting light.

  In the tread shape measuring method according to the present invention, it is desirable that the calculating step calculates a tread radius of a tire based on a distance measured by three or more laser displacement meters.

  In the tread shape measurement method according to the present invention, it is preferable that the calibration step is performed simultaneously with the calculation step for a tire that has already completed the measurement step.

  The tread shape measuring method of the present invention is a method of measuring the tread surface shape of a tire using a plurality of laser displacement meters arranged at intervals in the tire axial direction, and calibrating each laser displacement meter And a measurement step for measuring a distance in the tire radial direction from each laser displacement meter calibrated in the calibration step to the tread surface, and a calculation step for calculating a tread surface shape based on the distance measured in the measurement step .

  The calibration process includes an optical axis adjustment process. In the optical axis adjustment step, the optical axes of the laser displacement meters are adjusted in parallel to each other within a plane including the tire axis. Thereby, the shape of the tread surface, for example, the tread radius can be measured on the tire meridian section including the tire shaft.

  Further, in the optical axis adjustment step, the optical axis of each laser displacement meter is adjusted perpendicularly to the tire axis. Thereby, the laser light emitted from each laser displacement meter is directed in the tire radial direction, and the distance in the tire radial direction from each laser displacement meter to the tread surface can be accurately measured.

It is a perspective view which shows one Example of the tread shape measuring apparatus used for the tread shape measuring method of this invention. It is the top view which looked at the principal part from the upper part. It is the conceptual diagram which looked at the internal structure of the laser measuring apparatus from the side. It is a fragmentary perspective view explaining the effect by a wide laser beam. It is a flowchart which shows the process sequence of the tread shape measuring method of this invention. It is a flowchart which shows the process sequence of calibration process S1 of FIG. It is a perspective view which shows the outline | summary of the optical axis adjustment process S11 of FIG. It is a perspective view which shows the specific method of adjusting the optical axis of laser displacement meter 5c, 5s, 5s. (A), (B) is a conceptual diagram explaining the origin adjustment process S12 and the gain adjustment process S13 of FIG. It is a conceptual diagram which shows the process of measuring tread radius TRs, and the process of measuring tread radius TRm.

Hereinafter, embodiments of the present invention will be described in detail.
As shown in FIGS. 1 and 2, the tread shape measuring device 1 used in the tread shape measuring method of the present invention includes a tire holder 2 and a laser measuring device 3. The tire holder 2 has a support shaft 4 that supports a tire T filled with internal pressure so as to be rotatable about a tire axis j. The laser measuring device 3 includes a plurality of laser displacement meters 5 that measure the radial distance to the tread surface Ts of the rotating tire T.

  The shape measurement of the tread surface Ts is preferably performed as part of the tire production process. This is because when an abnormality in the tread surface Ts is found, measures can be taken immediately by going back to the previous process. Therefore, the tread shape measuring apparatus 1 is installed on the tire production line, for example, on the post-process side of the vulcanizer.

  The tire holding machine 2 of this example includes a support shaft 4 that horizontally supports the rim-assembled tire T, and drive means (not shown) such as a motor that rotates the support shaft 4 at a predetermined rotational speed. . However, the support shaft 4 can be configured to support the tire T vertically, and a road wheel that directly presses the tire T while being in pressure contact with the tread portion can be used as a driving means. In this example, as the tire T, five circumferential land portions R extending in the tire circumferential direction on the tread surface Ts, specifically, a central center land portion Rc and middle land portions Rm and Rm on both sides thereof, A tire for a passenger car having a rib pattern in which outer shoulder land portions Rs and Rs are arranged is illustrated.

  The laser measuring device 3 includes a moving table 6, five laser displacement meters 5 arranged in the moving table 6, and tread radius based on radial distance data y measured by the laser displacement meter 5. And calculating means 7 for calculating TR. A computer device having a CPU, a memory and the like is applied to the calculation means 7.

  Specifically, the laser measurement apparatus 3 of the present example includes a gantry 8 and a first moving pedestal 10 supported by the gantry 8 via a guide unit 9 so as to be movable in a Z direction perpendicular to the tire axial direction X. And a second moving table 12 supported by the first moving table 10 through the guide means 11 so as to be movable in the tire axial direction X. The second moving table 12 constitutes the moving table 6.

  As the guide means 9 and 11, those of various known structures can be used, and in this example, as shown in FIG. 2, a guide rail extending linearly and a guide groove guided by the guide rail are provided. Things are shown. The guide means 9 includes a cylinder 9 </ b> A that is fixed to the gantry 8 and extends in the Z direction, and its rod end is connected to the first moving table 10. Therefore, the first moving base 10 can move in the Z direction between the standby position Q1 and the measurement position Q2 by expansion and contraction of the cylinder 9A. The guide means 11 is attached to the ball screw shaft 11A that is pivotally supported by the first moving table 10 and extends in the tire axial direction X, and the moving table 6 (the second moving table 12 in this example) and is screwed to the ball screw shaft 11A. Nut portion 11B. Accordingly, the movable table 6 can freely move in the tire axial direction X by the rotation of the ball screw shaft 11A by the motor Mc.

  As shown in FIG. 3, the five laser displacement meters 5 are spaced apart from each other in the tire axial direction X. In this example, the five laser displacement meters 5 are disposed on the central laser displacement meter 5c and on both sides thereof. The intermediate laser displacement meters 5m and 5m and the outer laser displacement meters 5s and 5s disposed on both sides thereof are also included.

  The central laser displacement meter 5c is fixed to the moving table 6, and therefore can move in the tire axial direction X together with the moving table 6. Each of the intermediate laser displacement meters 5m and 5m is supported by the movable table 6 so as to be movable in the tire axial direction X via the guide means 13, respectively. That is, the intermediate laser displacement meter 5m can move relative to the central laser displacement meter 5c in the tire axial direction X. Each of the outer laser displacement meters 5 s and 5 s is supported by the movable table 6 so as to be movable in the tire axial direction X via the guide means 14. That is, the outer laser displacement meter 5s can move in the tire axial direction X relative to the central laser displacement meter 5c and the intermediate laser displacement meter 5m.

  Therefore, for example, the central laser displacement meter 5c can be aligned with the reference position on the tire equator Co by the movement of the movable table 6 itself by the guide means 11. The guide means 13 and 14 move the intermediate laser displacement meter 5m and the outer laser displacement meter 5s to appropriate measurement positions based on the central laser displacement meter 5c according to the tire size and tread pattern. be able to.

  As shown in FIG. 2, at the measurement position Q2, the laser displacement meters 5 are arranged so that the irradiation-side optical axis Li is parallel on one radiation surface extending from the tire axis j.

  As the guide means 13 and 14, various well-known structures can be used. In this example, as shown in FIG. 3, the guide shaft 15A and the ball screw shaft 16A spanned between the side plates of the movable table 6 and the laser displacement meter mounting plate 17 are attached to the guide shaft 15A and guided to the guide shaft 15A. 15B and a nut portion 16B screwed onto the ball screw shaft 16A. Therefore, the intermediate laser displacement meter 5m and the outer laser displacement meter 5s can be independently moved freely in the tire axial direction X by the rotation of the ball screw shaft 16A by the motors Mm and Ms.

  As each laser displacement meter 5, as shown in FIG. 4, a laser beam L having a width W of 5 mm or more is employed. In such a laser displacement meter 5, for example, with respect to the unevenness 18 (for example, unevenness caused by the sipe 18 a, the notch 18 b, etc.) on the tread surface Ts locally present in the irradiated portion La of the laser light L It is removed by the filtering function of the displacement meter 5 itself. Therefore, there is an advantage that generation of noise data due to local unevenness 18 can be suppressed. On the other hand, when the entire laser light irradiated portion La such as the lateral groove 19 falls in the unevenness, it becomes noise data. However, this noise data is detected and deleted by a smoothing process to be described later by the calculating means 7.

  Hereinafter, the tread shape measuring method of the present invention will be described. FIG. 5 is a flowchart showing a processing procedure of the tread shape measuring method.

  The tread shape measuring method includes a calibration step S1 for calibrating each laser displacement meter 5, a measurement step S2 for measuring a distance in the tire radial direction from each laser displacement meter 5 calibrated in the calibration step S1 to the tread surface Ts, and And a calculation step S3 for calculating the tread surface shape based on the distance measured in the measurement step S2.

  In the tread shape measuring method of the present invention, since a plurality of laser displacement meters 5 are used simultaneously, high accuracy is required for each laser displacement meter 5. Therefore, prior to the measurement step S2 and the calculation step S3, a calibration step S1 is executed, and each laser displacement meter 5 is calibrated. The calibration step S1 is not necessarily performed before the measurement step S2 for each tire, but it is desirable to calibrate each laser displacement meter 5 periodically in order to accurately measure the tread shape.

  FIG. 6 is a flowchart showing the processing procedure of the calibration step S1. The calibration step S1 includes an optical axis adjustment step S11 for adjusting the optical axis of each laser displacement meter 5, an origin adjustment step S12 for adjusting the origin of each laser displacement meter, and a gain adjustment for adjusting the gain of each laser displacement meter 5. And step S13. The optical axis adjustment step S11 need not be executed for all the calibration steps S1, but it is desirable to periodically adjust the optical axis of each laser displacement meter 5 in order to accurately measure the tread shape.

  FIG. 7 shows an outline of the optical axis adjustment step S11. In the figure, the optical axis adjustment of the three laser displacement meters 5c, 5s, and 5s is shown, but the same applies to the optical axis adjustments of the other laser displacement meters 5m and 5m.

  In the optical axis adjustment step S11, the optical axes Lc, Ls, Ls of the laser displacement meters 5c, 5s, 5s are adjusted in parallel with each other in a plane PL (a plane extending radially from the tire axis j) including the tire axis j. The Thereby, on the plane PL including the tire axis j, that is, on the tire meridian section, the shape of the tread surface Ts, for example, the radius of the arc connecting the three points on the land portions Rc, Rs, Rs, that is, the tread radius TR can be measured. Become.

  In the optical axis adjustment step S11, the optical axes Lc, Ls, Ls of the laser displacement meters 5c, 5s, 5s are adjusted perpendicularly to the tire axis j. As a result, the laser light emitted from each laser displacement meter 5c, 5s, 5s is directed in the tire radial direction, and the distance Y1, Y2 in the tire radial direction from each laser displacement meter 5c, 5s, 5s to the tread surface Ts. , Y3 can be measured accurately. The tread radius TR can be calculated using the distances Y1, Y2, and Y3 as described later.

  FIG. 8 shows a specific method for adjusting the optical axes of the laser displacement meters 5c, 5s, and 5s as described above. In the optical axis adjustment step S11 of the present embodiment, a calibration plate 60 having an irradiation surface 61 on which the laser light L emitted from each laser displacement meter 5c, 5s, 5s is irradiated is used. The calibration plate 60 is disposed so as to be able to appear and retract between the support shaft 4 and the laser displacement meters 5c, 5s, and 5s with the irradiation surface 61 facing the laser displacement meters 5c, 5s, and 5s.

  The calibration plate 60 is provided between the support shaft 4 and the laser displacement meters 5c, 5s, and 5s so that the irradiation surface 61 and the plane extending radially from the tire axis j are perpendicular to each other. The calibration plate 60 is provided so as to be movable in the tire radial direction along the plane PL (see FIG. 7). The calibration plate 60 is driven by driving means such as a cylinder (not shown) and moves in the tire radial direction. Other driving means may be used for driving the calibration plate 60.

  On the irradiation surface 61, for example, a straight line 62 indicating an intersection with the plane PL including the tire axis j is drawn. The positions and orientations of the laser displacement meters 5c, 5s, and 5s are finely adjusted so that the laser beams emitted from the laser displacement meters 5c, 5s, and 5s are irradiated on the straight line 62. The positions and orientations of the laser displacement meters 5c, 5s, and 5s are finely adjusted by, for example, inserting shims between the laser displacement meter mounting plate 17 shown in FIG. 3 and the laser displacement meters 5c, 5s, and 5s. sell. Thereby, the optical axes Lc, Ls, Ls of the laser displacement meters 5c, 5s, 5s are positioned in the plane PL.

  Next, the calibration plate 60 is moved in the tire radial direction. The moving direction of the calibration plate 60 may be either inward or outward in the tire radial direction. At this time, when the optical axes Lc, Ls, Ls of the laser displacement meters 5c, 5s, 5s are perpendicular to the tire axis j, the irradiation positions Pc, Ps, Ps of the respective laser beams on the irradiation surface 61 Is immutable. Therefore, when the calibration plate 60 is moved in the tire radial direction, the positions and postures of the laser displacement meters 5c, 5s, and 5s are finely adjusted so that the deviation amounts of the irradiation positions Pc, Ps, and Ps become sufficiently small. The Thereby, the optical axes Lc, Ls, and Ls of the laser displacement meters 5c, 5s, and 5s are adjusted to be parallel to each other and perpendicular to the tire axis j in the plane PL.

  When the moving distance D in the tire radial direction of the calibration plate 60 is 10 to 30% of the outer diameter of the tire T whose tread shape is measured, a preferable range of the deviation amounts of the irradiation positions Pc, Ps and Ps is 2 mm or less. A more preferable range is 1 mm or less. When the deviation amounts of the irradiation positions Pc, Ps, and Ps are 2 mm or less, the measurement errors of the laser displacement meters 5c, 5s, and 5s are small, and the influence on the tread radius TR is small. In addition, the deviation | shift amount of irradiation position Pc, Ps, Ps is easily confirmed by visual observation etc. by marking the irradiation position Pc, Ps, Ps on the irradiation surface 61 before moving the calibration board 60, for example. it can.

  In the present embodiment, the irradiation surface 61 is made of a material including rubber (for example, silicon rubber). The irradiation surface 61 made of such a material can suppress irregular reflection of the laser light L, and the optical axis can be adjusted easily and efficiently. From the viewpoint of suppressing the irregular reflection of the laser beam L, it is also effective to color the irradiation surface 61 in black or to perform rough processing.

  FIG. 9 conceptually shows the calibration jig 30 used in the origin adjustment step S12 and the gain adjustment step S13. The calibration jig 30 includes a cylindrical base portion 31 supported by the support shaft 4 and a reflection plate 32 that is integrally attached to the base portion 31. The reflector 32 includes a first reflector 32a that is separated from the axial center 4i (corresponding to the tire axis j) of the support shaft 4 by a known distance F1 in the radial direction, and radially inward and outward from the first reflector 32a. And second reflectors 32b and 32c that are separated by a known distance F2. The distance F1 is preferably a value that approximates the radius of the tire T whose tread shape is measured, for example. The distance F2 is desirably a value that approximates the camber amount that is the distance in the tire radial direction between the tire equator position on the tread surface Ts and the tread ground contact edge, for example. The reflecting plates 32a, 32b, and 32c are arranged at intervals in the circumferential direction.

  In the origin adjustment step S12 (see FIG. 6), first, the origin that is the reference position for measuring the distance with each laser displacement meter 5 is adjusted using the first reflector 32a. The origin adjustment is performed based on the specifications of each laser displacement meter 5.

  Next, in the gain adjustment step S13 (see FIG. 6), the gain adjustment of each laser displacement meter 5 is performed using the second reflecting plates 32b and 32c. Gain adjustment is also performed based on the specifications of each laser displacement meter 5. In the gain adjustment step S13, the gain of each laser displacement meter 5 may be adjusted using the first reflector 32a and the second reflector 32b or 32c.

  The reflecting surfaces of the first and second reflecting plates 32a, 32b, and 32c are preferably formed of convex cylindrical surfaces having radii of curvature r1, r2, and r3 that are equal to the distance from the axis 4i. That is, r1 = F1, r2 = F1 + F2, and r3 = F1-F2. As a result, when the reflecting plates 32a, 32b, and 32c are repositioned around the axis 4i, the laser light L is accurately reflected even when the repositioning angles of the reflecting plates 32a, 32b, and 32c are slightly shifted. And the calibration process can be expedited.

  By adjusting the origin of each laser displacement meter 5 by the origin adjustment step S12 and appropriately adjusting the gain of each laser displacement meter 5 by the gain adjustment step S13, the measurement accuracy of each laser displacement meter 5 can be increased. In the present embodiment, prior to the origin adjustment step S12, the optical axis of each laser displacement meter 5 is accurately adjusted in the optical axis adjustment step S11, so the accuracy of origin adjustment and gain adjustment of each laser displacement meter 5 is improved. It is further enhanced.

  Hereinafter, the measurement step S2 and the calculation step S3 shown in FIG. 5 will be described. In this example, as shown in FIG. 10, a center land portion Rc extending on the tire equator in the tire circumferential direction, a pair of middle land portions Rm extending on both sides of the center land portion Rc in the tire circumferential direction, and each middle land portion Rc. The tread shape of a tire having a pair of shoulder land portions Rs extending outward in the tire axial direction in the tire circumferential direction is measured.

  For example, in the measurement step S2, the distance in the tire radial direction from each laser displacement meter 5 at one point on the center land portion Rc and one point on the shoulder land portions Rs and Rs of the five circumferential land portions R is measured. Is done. In the calculation step S3, the tread radius TRs connecting the three points is calculated. Further, in the measurement step S2, the distance in the tire radial direction from each laser displacement meter 5 at one point on the center land portion Rc and one point on the middle land portions Rm, ms of the five circumferential land portions R is measured. May be. In this case, in the calculation step S3, the tread radius TRm connecting the three points is calculated.

  The reason for measuring the two tread radius TRs, TRm is, for example, that the relationship between the tread radius TRs and the handling stability is strong in the usage conditions (air pressure, load, etc.) in country A, and the tread radius TRm in the usage conditions in country B. This is because the correlation with the steering stability changes depending on the use conditions of the tire and the like, for example, the correlation between the vehicle and the steering stability becomes strong. Therefore, it is possible to more accurately evaluate the steering stability by measuring the two tread radius TRs and TRm.

  Below, measurement process S2 and calculation process S3 in the case of calculating tread radius TRs are demonstrated.

  In the measuring step S2, the laser light L is irradiated from the three laser displacement meters 5 out of the five laser displacement meters 5 to the tread surface Ts of the tire T rotating around the tire axis, respectively. The radial distances Y1, Y2, Y3 to the surface Ts are measured. Thereby, m pieces of radial direction distance data y1, y2, y3 for each laser displacement meter 5 are acquired per tire circumference.

  When calculating the tread radius TRs, m pieces of radial distance data y1 to the center land portion Rc are acquired by the central laser displacement meter 5c per tire circumference. That is, m pieces of radial direction distance data y11 to y1m are acquired. In addition, m pieces of radial distance data y2 and y3 to the shoulder land portions Rs and Rs are acquired by the laser displacement meters 5s and 5s on the outer sides, respectively. That is, m pieces of radial distance data y21 to y2m and data y31 to y3m are acquired. The radial distance data y11 to y1m, y21 to y2m, and data y31 to y3m are transferred to the calculation means 7 and stored.

  The calculating means 7 performs calculation process S3. In the calculation step S3, smoothing processing is performed on each of m pieces of radial distance data y1, y2, and y3, and noise data due to the lateral grooves 19 is removed. Then, the radial distance data y1, y2, and y3 after removing the noise data are averaged to obtain average values y1N, y2N, and y3N.

  In the smoothing process, the i-th data yi obtained in time series for each of the m radial distance data y1, y2, and y3 obtained, and the latest k pieces of data obtained before that. Is compared with a moving average yN that is an average value of. When the difference | yi−yN | is larger than the threshold value, the data yi is deleted from the radial distance data y1, y2, and y3 as noise data.

  Specifically, the latest k pieces of data obtained prior to the i-th data yi mean yi-1 to yi-k. The moving average yN that is the average value of the most recent k pieces of data means (yi-1 + yi-2 +... + Yi-k) / k.

  In the case of the radial distance data y1, the i-th data yi is y1i, and the nearest k pieces of data yi-1 to yi-k are y1i-1 to y1i-k. The moving average yN means (y1i-1 + y1i-2 + ... + y1i-k) / k. The same applies to the radial distance data y2 and y3.

  Then, the computing means 7 compares the difference | yi−yN | between the moving average yN and the data yi with a threshold, and when the difference | yi−yN | is larger than the threshold, the data yi is deleted as noise data. The computing means 7 performs this operation in order from i = 1 to i = m. When k ≧ i, yi−1, yi−2, ˜y1, ym, ym−1, ˜ym− (ki) are adopted as the latest k pieces of data. Here, as the threshold value, a value larger than the assumed RR0 and a value smaller than the groove depth of the lateral groove 19 arranged in the circumferential land portion R to be measured are selected. Usually set to about 3.0 mm.

Thereafter, the calculation means 7 calculates the average values y1N, y2N, y3N and the tire axial distances x1, x2, x3 from the tire axial reference position (can be set arbitrarily) X to each laser displacement meter 5. Tread radius TR is calculated from the above. Specifically, the tread radius TR, which is the radius of curvature, can be obtained by substituting three points P (x1, y1N), P (x2, y2N), and P (x3, y3N) into the following equation (1). it can.
(Xa) ² + (y−b) ² = TR ^2- (1)

  The measurement step S2 and the calculation step S3 when calculating the tread radius TRm using the laser displacement meters 5c, 5m, and 5m are the same as described above. Note that the measurement step S2 and calculation step S3 when calculating the tread radius TRs and the measurement step S2 and calculation step S3 when calculating the tread radius TRm can be performed simultaneously. At this time, the radial distance data y1 acquired by the central laser displacement meter 5c, the average value y1N after smoothing the radial distance data y1, and the like can be used in common.

  Since the calculation step S3 involves a smoothing process for complicated calculations such as moving averages, the amount of data to be handled becomes enormous depending on the number m of radial distance data acquisition and the number k of moving averages, and a corresponding time is required. There is. In such a case, the calibration step S1 is preferably performed simultaneously with the calculation step S3 for the tire that has already completed the measurement step S2.

  The number m of the radial distance data acquisitions is preferably 500 or more. If the number m is less than this, the correlation between the tread radius and the steering stability tends to decrease. The upper limit of several meters is not particularly limited, but if it is too large, the processing becomes complicated and time is wasted. Therefore, the upper limit of several meters is preferably 2000 or less.

  The moving average number k is preferably 100 to 200000, more preferably 1000 to 20000. If the number k is less than 100, the accuracy of the smoothing process may decrease. On the other hand, when the number k exceeds 200,000, the smoothing process becomes complicated and time is wasted. Furthermore, in order to increase the accuracy of the smoothing process, it is preferable to set the rotation speed of the tire T in a range of 20 to 300 rpm, and when the rotation speed is less than 20 rpm, the accuracy is lowered. Moreover, if it exceeds 300 rpm, it will be difficult to acquire 500 or more radial direction distance data per round.

  Further, in order to increase the filtering accuracy by the laser displacement meter 5, as shown in FIG. 5, the width W of the laser light L is in the range of 10 to 70% of the width WR of the circumferential land portion R to be measured. Is preferred. When the width W of the laser beam L is less than 5 mm or less than 10% of the width WR, the ratio of the sipe 18a, the notch 18b, etc. in the irradiated portion La increases, and the filtering function is not sufficiently exhibited. On the other hand, if it exceeds 70%, the laser beam L may protrude from the circumferential land portion R.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  Using the measuring apparatus shown in FIG. 1, according to the measuring method of the present invention, 20 tread radius TRs of pneumatic tires (195 / 65R15) were measured according to the specifications shown in Table 1, and the average value and standard deviation σ were calculated. The tread pattern is a 5 rib pattern.

  For comparison, data measured without using a calibration plate is referred to as Comparative Example 1.

  As is clear from Table 1, it was confirmed that the tread shape measuring method of the present invention can measure the tread radius TRs more accurately than the comparative example.

DESCRIPTION OF SYMBOLS 1 Tread shape measuring apparatus 3 Laser measuring apparatus 4 Support shaft 5 Laser displacement meter 7 Calculation means 30 Calibration jig 31 Base 32a First reflecting plate 32b Second reflecting plate 32c Third reflecting plate 60 Calibration plate 61 Irradiation surface j Tire axis L Laser beam Lc, Ls Optical axis R Circumferential land portion Rc Center land portion Rs Shoulder land portion Rm Middle land portion S1 Calibration step S2 Measurement step S3 Calculation step S11 Optical axis adjustment step S12 Origin adjustment step S13 Gain adjustment step T Tire TR tread Radius Ts tread surface

Claims (7)

A tread shape measuring method for measuring the tread surface shape of a tire using a plurality of laser displacement meters arranged at intervals in the tire axial direction,
Based on the calibration step for calibrating each laser displacement meter, the measurement step for measuring the distance in the tire radial direction from each laser displacement meter calibrated in the calibration step to the tread surface, and the distance measured in the measurement step And calculating a tread surface shape.
The calibration step, the optical axes of the laser displacement meter, viewed including the optical axis adjustment process of adjusting perpendicular to mutually parallel, and tire axis in a plane including the tire axis,
In the optical axis adjusting step, a calibration plate having an irradiation surface irradiated with laser light emitted from each laser displacement meter is moved in the tire radial direction along the plane, and laser light on the irradiation surface is obtained. A tread shape measuring method, wherein the optical axis of each laser displacement meter is adjusted based on the amount of deviation of the irradiation position . The optical axis adjustment step adjusts the optical axis of each laser displacement meter so that the deviation amount is 2 mm or less when the moving distance of the calibration plate is 10 to 30% of the outer diameter of the tire to be measured. The tread shape measuring method according to claim 1. The tread shape measuring method according to claim 1, wherein the irradiation surface is made of a material containing rubber . A tread shape measuring method for measuring the tread surface shape of a tire using a plurality of laser displacement meters arranged at intervals in the tire axial direction,
Based on the calibration step for calibrating each laser displacement meter, the measurement step for measuring the distance in the tire radial direction from each laser displacement meter calibrated in the calibration step to the tread surface, and the distance measured in the measurement step And calculating a tread surface shape.
The calibration step includes an optical axis adjustment step of adjusting the optical axes of the laser displacement meters in parallel to each other in a plane including the tire axis and perpendicular to the tire axis, and the optical axis in the optical axis adjustment step. Including an origin adjustment step of adjusting the origin of each adjusted laser displacement meter,
In the origin adjustment step, a laser beam is emitted from each of the laser displacement meters to a first reflector that is separated from the axis of the support shaft by a known distance F1 in the radial direction at a base portion supported by the support shaft of the tire. The tread shape measuring method characterized by being performed by this . The tread shape measurement method according to claim 4, further comprising a gain adjustment step of adjusting a gain of each laser displacement meter whose origin is adjusted in the origin adjustment step . 6. The gain adjusting step is performed by emitting laser light from each of the laser displacement meters to a second reflecting plate that is separated from the first reflecting plate by a known distance F2 radially inward or outward. tread shape measuring method. A tread shape measuring method for measuring the tread surface shape of a tire using a plurality of laser displacement meters arranged at intervals in the tire axial direction,
Based on the calibration step for calibrating each laser displacement meter, the measurement step for measuring the distance in the tire radial direction from each laser displacement meter calibrated in the calibration step to the tread surface, and the distance measured in the measurement step And calculating a tread surface shape.
The calibration step includes an optical axis adjustment step of adjusting the optical axes of the laser displacement meters parallel to each other in a plane including the tire axis and perpendicular to the tire axis,
The calculating step calculates a tread radius of the tire based on a distance measured by each of the three or more laser displacement meters,
The tread shape measurement method , wherein the calibration step is performed simultaneously with the calculation step for a tire that has already completed the measurement step .

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