DE2248789A1 - FRICTION WHEEL LENGTH KNIFE - Google Patents

Description

The invention is concerned with a friction wheel length measuring device of the type, for example, in the
US Patents 3,311,985 and 3,378,929 is described "

A measuring device operating according to these patents can be attached to a lathe slide
and, for example, drive along the lathe bed during an operation. A friction wheel on the measuring device rests against a section of the lathe bed and rolls along on it when the slide is moved transversely. Translated in a common embodiment
a precision gear of the measuring device the rotation
the measuring wheel to get an indication on a scale or the like. Depending on your requirements, you can read off directly or you can use enlargement aids

ORIGINAL IMSFECTED

TELEGRAMS 3098 16/0297

can be used. Since the circumference of the wheel is precisely known, an exact length measurement of the displacement can be made the lathe can be obtained by reading the display. Of course, a length measuring instrument can can also be used on other machines or tools.

Precision length meters that work with a friction wheel are extremely widespread and can serve many different purposes. A widely used measuring device sold by the applicant is known under the designation "TRAV-A-DIAL". Such gauges are calibrated in units of five-ten thousandths of an inch, or 0.01 cm, or even 0.0001 inches. The measured length is equal to the circumference of the measuring wheel, which is monitored very precisely before the length indicator rotates again. A friction wheel length meter whose measuring range is a multiple of the measuring wheel circumference is marketed by the applicant under the designation ¹¹ TEDD ¹¹ . Such a device covers a length of 100 inches or more before the length indicator begins a new revolution. However, measuring devices with such a large measuring range present problems with regard to the exact repeatability of the measuring display.

The accuracy of a measuring instrument is defined as the instrument's ability to accurately measure length to be displayed after running over the path to be measured? gen. For example, the accuracy can be set in that the measuring instrument has a large Accuracy known path is performed, which is determined, for example, with conventional gauges or the like can be. When a length measuring instrument has a path

309816/0297

of 10 inches in length according to the standard specification, the gauge should be exactly 10 inches. Accuracy is a measure of the instrument's ability to perform a to deliver such a result.

Repeatability is a measure of the instrument's ability to show the value "zero" if it is after a movement away from its initial position. is returned to its original position. The measuring instrument For example, it can be zeroed back and forth several times over a distance of 50 inches be guided and then returned to its original position. Any deviation from a zero value after Return to the starting position is considered a repeatability error. It has been found that such Repeatability errors are caused by mechanical hysteresis in the measured devices or in the Have type of attachment for the measuring device. This mechanical hysteresis is mainly due to non-reciprocal elastic deformations, so that after several such back and forth runs an essential. Errors can add up.

A length measuring instrument can have a high degree of accuracy and essentially no repeatability problems if it is only used over short lengths, while using the same instrument at exactly the same Mounting in a machine tool can show repeatability errors with no change in accuracy, though it is used a number of times over greater lengths. The size of the repeatability error can be qleiehern measuring instrument from a machine tool to other sway even if the machine tool! normally are identical.

3098 1 6/0297

In U.S. Patents 3,307,265 and 3,561,121, friction wheel length meters are described in which the friction wheel has a curved surface on its circumference, so that the effective radius and thus the The circumference of the measuring wheel can be changed by tilting the length meter across the measuring path can. Such a device improves the accuracy of the length measurement by the device. In the U.S. Patent 3,561,120 disclose measures for improvement the repeatability of the measurements of a friction wheel length meter described, according to which the measuring instrument runs obliquely relative to the direction of the path to be measured. Figures A, B and C show in plan view and in side views a length measuring instrument with friction wheel. Although these figures are an instrument after To explain the state of the art, they show schematically an instrument that can also be used according to FIG Invention is suitable.

In these figures, a measuring wheel 11 is rotatably mounted in an instrument housing 10. The measuring wheel 11 extends with a small part of its periphery through the housing delimitation. A button 12 is connected to the wheel 11 and carries calibration marks, not shown, which can be read on the top of the measuring instrument. One full turn of the knob usually corresponds to one full turn of the wheel. In some embodiments an arrangement can be used in which the button only after several revolutions of the measuring wheel circulates once. Inside the housing 10 is a conventional transmission gear (not shown) arranged without a dead gear that connects the wheel 11 to a scale 13 that is in thousandths of an inch or hundredths of a second Centimeter is calibrated as required. The calibration marks on the button 12 thus give a rough indication

3098 16/0297

the distance covered by the wheel, while the dial pointer provides the associated fine display. When the wheel has a circumference of 6 inches, the display repeats itself every 6 inches. In others, not shown In some embodiments, an electronic sensor is provided for the wheel rotation, which adds up the revolutions, so that several sizes can be scrolled before the display repeats itself. Of course, others can too Indicators, motion translators, and the like can be used.

The measuring instrument is on a movable part 14 of a machine tool via a support 16, which here is only is shown schematically, be attached. The easy one Part 14 can, for example, be a slide of a lathe or another movable part of a work- '. be a machine tool. The measuring wheel 11 of the instrument is in frictional engagement with a fixed section 17 of the machine, for example with a guide for the machine bed; this frictional engagement is achieved by means of a support on the Housing 10 causes acting clamping force. Thus, when the slide 14 runs along the lathe bed, it rolls the wheel 11 along the guide 17, whereby the knob 12 and the scale 13 are rotated. By reading on The covered length can be measured on the button and on the scale.

The support mentioned here or the attachment plate can have a diverse design in detail, those for using the measuring instrument on a machine tool is necessary and can also have the necessary adjustment devices. The mounting plate can take many forms depending on the type and design of the machine tool, and a large number are more common and more particularly mounting plates are known. So can

309816/0297

the support can be, for example, a mounting plate as described in US Pat. No. 3,378,929 where a compression spring presses the instrument against the measuring surface have, as in U3- »Patent 3 307 is mentioned, which connects the measuring instrument with the tool and also adjustable the angle between the two power. A variety of other adjusters for the angle and tension of the instrument are available familiar to the person skilled in the art, so that the support or the mounting plate are only shown here in general

In the figures A, B and C are Cartesian coordinates with respect to the measuring surface on which the measuring wheel 11 runs, registered. The direction X represents the main direction of the measuring path, for example along the guide 17 The X axis would be approximately a tangent to the measuring wheel 11. The Z axis points perpendicular to the main direction of the cycle path and approximately parallel to the axis of rotation of the wheel. The Y-axis is of course perpendicular to the X-axis and the Z-axis and the XY plane is approximately the plane in which the measuring wheel 11 lies.

As will be explained below, the measuring device must also be positioned at a correct angle for an accurate reading. Therefore, an angle * ^ "is defined as a rotation around the Y-axis (Fig. C). According to the terminology used here, this is also referred to as the ^M skew" of the measuring wheel. Another angle of interest is the inFig. A shown angle /, which represents a measure of the rotation of the measuring instrument about the X-axis and is referred to here as "tilt". It should be noted that in the drawings the angles * G and ^ y are shown greatly exaggerated for purposes of explanation. Note further that when adjusting the angle of the

309816/0297

Measuring instrument the center points of the actual rotation often not with the center of the coordinate system coincide. Their exact location is typically determined by the respectively selected support 16. According to US Pat. No. 3,561,121, the measuring wheel preferably has a relatively larger radius and thus circumference on one side and a relatively smaller radius on the other side, the intermediate surface of the periphery being curved. In the one shown in Figures A, B and C. Instrument lies, the line of maximum wheel circumference in a plane perpendicular to the axis of rotation of the wheel and is closer on the lower side of the wheel than on the upper side. When the measuring instrument is aligned so that the axis of rotation of the wheel is perpendicular to the Y-axis. (WinkelV = 0), then the line of maximum wheel circumference touches the stationary one Section 17 of the machine tool. If further the measuring instrument to increase the angle ^ / (Fig.A) tilted then lays the contact point between the wheel and the fixed portion 17 on a line of smaller circumference.

The support base 16 is a conventional component and, for example, in the aforementioned US patents described. Various types of adjustment devices in connection with the base used in the usual way. For example, the position of the instrument along the Y-axis cannot be changed by one adjusted dovetail. In addition to the adjustment in the Y direction, there are facilities for this intended to apply a spring force to the instrument in order to achieve a relatively large (for a TRAV-A-DIAL device recommended 40 Ib) and preferably a substantially constant load between the measuring wheel and the measuring surface to have. This force ensures frictional engagement and reduces the possibility of the

309816/0297

Wheel of the lead to a substantial and unpredictable measurement error can lead. The metal elastic crowding see US Patent 3 307 265, the must be compensated to achieve the accuracy, results from the measuring wheel on a small area force exerted on the measuring surface., Even with relatively The metal-elastic feed can be significant because the contact area is equilateral relative to small forces is small. The effect does not increase linearly with increasing force and a substantial force is preferred to to reduce the size change of the effect due to smaller changes in force.

The support base 16 also has set screws, not shown or the like in order to incline the instrument around the Y-axis by an angle and around the instrument to bend the X-axis by an angle ν · The Movement of the instrument during the setting of the skew actually takes place around an axis which is shifted relative to the point of contact between the measuring wheel and the measuring surface. So when the angle changes a slight rotation of the wheel in contact with the measuring surface can occur. Similarly, it becomes the center of instrument rotation moved out of the point of contact between wheel and measuring surface when the fold is changed, was flatter it has hitherto been desirable to keep the spring loading of the instrument against the measuring surface during the accuracy adjustments only to be completely removed or reduced to avoid overloading the spring system and possible damage of the instrument.

3098 16/0297

As stated in US Pat. No. 3,561,121, a local deformation (metaXlelastic advancement) called, in the wheel and in the measuring surface on which the wheel runs, to a faulty, short length measurement guide through the friction wheel length meter. By . Bending the measuring instrument by a winkely. will the effective wheel circumference, which is in contact with the measuring surface, less, whereby that of the local deformation attributable error is compensated · Thus, the accuracy of the measuring instrument is maintained and the displayed lengths are exactly the same as the actual lengths covered. The local influences Deformations are reversible and their compensation ensures the desired accuracy. Local deformations do not lead to repeatability errors.

The repeatability text errors associated with the use of friction wheel length meters are caused by non-reproducible Press in both the components of the machine tool itself and the fastening device for the measuring device on the machine tool. Such deformations are very minor, but sufficient to generate repeatable text errors in a friction wheel gauge that uses over long lengths especially when a measurement is carried out repeatedly. The fact that such a measuring instrument the small elastic hysteresis dei: machine tool establishes, testifies to the extraordinarily large Accuracy and sensitivity of such devices.

In US Pat. No. 3,561,120 measures are taken for the attachment of a friction wheel measuring instrument proposed to compensate for repeatability errors and thereby essentially eliminate, which have their cause in the non-reproducible deformations. Repeatability

309816/0297

-IG-

errors will be made without affecting the accuracy avoided.

Own the individual components in the machine tool usually only one degree of freedom of movement. The machines are designed to prevent distractions in all other directions except for intended movement be depressed as much as possible · inevitable Displacements in other directions lead to errors Errors can still be caused by worn machines or by built-in tolerances, which means a certain "wobble" or a dead passage in the directions other than that intended. The measuring device is attached to a component of the machine in such a way that the measuring wheel rolls in frictional engagement on the surface of a second component that is parallel to the Direction of the desired relative movement between the components takes place. To compensate for repeatability errors, the size of such an error is first determined when the device is mounted so that the plane of rotation of the wheel is parallel to the relative direction of movement. The measuring device is then adjusted so that the plane of rotation of the measuring wheel is shifted from the parallelism to the relative direction of movement by an amount which compensates for the repeatability error.

This means that the measuring device is intentionally attached so that the measuring wheel is slightly at rest at an angle to the permitted relative direction of movement between the two components of the machine tool seems to be running and this slip angle is like that chosen so that its size automatically compensates for repeatability errors that would otherwise occur. One

309816/0297

such intended initial skew attachment-der Contrary to the expectation, the device does not produce any measurement accuracy errors, regardless on the amount of relative movement between the components. The term "relative movement" is used to denote the basically intended type of movement that must be available for the operation of the measuring device and for differentiation of those movements that only assume very small dimensions and are undesirable and, moreover, generate repeatability errors.

The skew technique for a measuring instrument does best can be taken from FIG. The instrument is initially oriented so that the plane of the wheel 11 is parallel to the XY plane. If a repeatability error is detected, the instrument may skew to be adjusted at the angle so that it is no longer runs parallel to the X-axis. The size of the angle * ^ around the the instrument should skew is determined empirically.

The adjustment of the measuring instrument with regard to repeatability errors is described in detail in U.S. Patent 3,561,120, previously mentioned. After that will be the indicators 12 and 13 of the measuring instrument are set so that they are in a known position, preferably Point to zero on a fixed stop of the instrument defined by the structure of the lathe. Of the Lathe slide or the like is then several times (for example 10 times) as far as possible along the lathe bed moved back and forth from its starting position. Because of the non-reciprocal deformations of the lathe, the measuring device can after the first revolution show a measurement error across the slide along the lathe bed, and these errors add up for

309816/0297

every cross run so that after several runs the display devices show a defined value, which is different from the initial zero setting. The mounting plate 16 is then so at stationary Adjusted slide that the fine indicator 13 shows a run of the measuring wheel in such a direction that the The pointer returns to the zero position. The size of the return towards the zero position depends on the The length of the advance, however, is typically sufficient to bring the dial pointer halfway to a zero position traced back.

The slide is then pushed back and forth several times along the lathe bed and the The accumulated residual errors indicated by the indicator are recorded. Then the skew of the measuring instrument adjusted again so that a skew mounting angle is reached gradually, which creates a corrective "error", the size of which is absolutely equal and opposite in sign to the repeatability error, that of the non-reproducible Deformation of the machine tool arises. Such adjustment can be tedious and tedious be time consuming and require a fairly precise initial adjustment of the measuring device, the plane of the measuring wheel is parallel to the XY plane. However, it is desirable to have such a precise initial adjustment to avoid and the difficulty as well as the time required for the necessary adjustment to compensate for the repeatability error without reducing the accuracy.

According to the invention, a device is therefore proposed that the sensitivity of a friction wheel removal

3098 16/0297

Measuring instrument compared to skew reduced, with several unevenly distributed ridges on the wheel circumference are distributed, the longitudinal axis of which runs transversely to the circumference of the measuring wheel.

These and other features and advantages of the invention will become apparent from the following description of a presently preferred embodiment of the invention reference being made to the accompanying drawings. Show in detail:

Figures A to C show a prior art measuring instrument;

Fig. 1 is a side view of a measuring wheel according to the invention;

FIG. 2 shows a side view of a section from the circumference of the wheel according to FIG. 1; and

FIG. 3 shows a schematic representation of the burrs on the wheel according to FIG. 1.

The actual cause of the repeatability error in a friction wheel length measuring instrument is to be seen in non-reciprocal deformations of the machine tool and the clamping with which the measuring instrument is attached to the machine tool. These deformations produce (1) an inclined course of the measuring wheel relative to the Hatspt relative direction of movement between the measuring wheel and the measuring surface; (2) fluctuations in the tilt (v ·) of the measuring wheel relative to the measuring surface; or (3) fluctuations in the contact force of the measuring wheel on the measuring surface. These three effects can be achieved either simultaneously or individually by non-reproducible deformation of the machine tool and the fastening device for the . Messinatru ment are caused.

309816/0297

The deformations of the machine tool and the fastening device are not reproducible in that they are of different nature and size in one direction of movement are along the machine tool relative to movement in the opposite direction. If the elastic deformations would be reciprocal, i.e. would be the same in both directions, the measuring instrument would Provide repeatable results · The degree of non-reciprocity, and hence the repeatability error, is not easily predictable and therefore becomes empirical determined by simply measuring the repeatability error.

The measuring instrument has six degrees of freedom relative to the measuring surface, namely translation along each of the three Directions and rotation or panning about each of these three axes. Only three of these six degrees of freedom are actually of importance in terms of measurement accuracy or repeatability. The rotation of the meter around the Y-axis (angle «^) creates a skew. the Rotation of the instrument around the X-axis (angle ^) produces a fluctuation in the effective diameter of the measuring wheel 11. The translation of the measuring instrument along the Y-axis can fluctuate due to the pressure force of the measuring wheel generate against the measuring surface, whereby the size of the metal-elastic feed is changed.

The inclination of the measuring wheel caused by the deformation skewing in the X direction is not directly a significant cause. The skew of the measuring wheel, however produces a change in the tilt * "of the measuring wheel and often also a difference between the pressure of the measuring wheel on the measuring surface during the movement of the instrument in one direction

309816/0297

about its movement in the opposite direction. The X-axis translation does not pose any problems themselves. The Z-axis translation is either problem-free because of the sliding of the measuring wheel parallel to its axis of rotation, or because of the force-applied pressure of the measuring wheel against the measuring surface, appears as an X-axis rotation (Winkely) due to the deformation of the fastening device for the measuring instrument. The Z-axis rotation is reflected in an "X-axis translation".

Because of the different coupling effects between the different degrees of freedom, the skew of the measuring wheel can altogether fluctuate in the tilt angle of the measuring wheel relative to the measuring surface and thus the effective wheel diameter. The coupling effects can also cause skew, which manifests itself as changes in the pressure applied by the measuring wheel manifested on the measuring surface, whereby the effect of the metal-elastic feed is changed. Both circumstances can lead to repeatability errors «,

Fig. 1 shows a side view ein.Meßrad H ₉ which is designed according to the invention. The measuring wheel 11 is shown enlarged in FIG. 1 for the purpose of explanation. In the currently preferred embodiment, the wheel has a first surface 21 and an opposite surface 22 lying parallel to this. The circumference 23 of the wheel has a curved profile, the radius of curvature preferably being greater than the radius of the wheel and the centers of curvature being asymmetrical, that the line 24 of greatest circumference is much closer to the lower surface 21 than to the upper surface 22 of the wheel. As already mentioned, the wheel circumference near the upper surface 22 is smaller than the wheel circumference near the lower surface 21.

309816/0297

edges of the wheel can therefore be varied the effective amount to any desired degree of accuracy as described in detail in U.S. Patent 3,561,121. The radius of the curved Area can be less than or equal to the radius of the wheel.

So far it has been customary to grind the measuring wheel for a measuring instrument in such a direction that the grinding marks extend in the circumferential direction around the wheel circumference, this was done for reasons of easier manufacture and also to maintain the circularity of the wheel, and to gain a precisely predetermined amount. The measuring wheels are sometimes used after grinding polished.

In contrast, it is provided according to the invention, the measuring wheel at least to grind in the last stage of its dressing in a direction that is transverse to the circumference of the measuring wheel lies. This leads to several irregularly distributed, sharp-edged degrees 26 on the periphery of the wheel, whose longitudinal axis extends transversely to the circumference. As a result, significantly better results are achieved and the Adjustment for repeatability is significantly simplified. The irregularity of the degree spacing is of of no particular importance, as will emerge from the following.

As will be explained, it is rather important that the largest mean distance between ridges is about ten thousandths of an inch (about 0.254 mm) and that the minimum mean distance between ridges is greater than about one microinch. Preferably the middle one is Distance between ridges at about a thousandth of an inch for best results. It is important, that the angle between the rise of the ridge near its apex and a tangent to the wheel at the

3098 1 6/0297

The tip of the ridge is significantly larger than the angle of static friction between the wheel and the surface to be measured, so that slip is excluded. It is also important that the ridges have a mean length across the circumference of the Wheel that is greater than about three times the mean distance between the ridges. This will achieved that a maximum force is exerted through the burrs in the correct circumference of the wheel, without the forces exerted in the axial direction are significantly increased. This further ensures that the wheel is on a measuring surface follows the same track, despite slight changes in the tilt of the wheel or translation in the Z direction.

For explanation it is assumed that the length measuring instrument is on a lathe slide for the feed in the main direction of the lathe bed, i.e. in the X-direction. The Keßrad 11 of the length measuring instrument lies against a guide of the lathe bed to the size of the advance of the slide along the To measure the bed. The lathe guide thus represents the measuring surface. If a state-of-the-art, smooth or in the circumferential direction ground friction measuring wheel is rolled along over the guide, can a repeatability error may occur because of a specific Point on the measuring wheel touches a given point on the guide during the forward thrust and slightly will be shifted from this predetermined point when the feed is reversed. This occurs because no measures ensure that the measuring wheel exactly the same track during the forward thrust and the Backward thrust follows. Exact repeatability could be obtained if the measuring surface was in the form of a rack with teeth and the measuring wheel would be a pinion with teeth that mesh with those on the rack.

309816/0 297

Since the pinion necessarily pushes the Must follow the rack, absolute repeatability would be ensured. Some known measuring wheels have a Pinion that presses teeth on a measuring surface and necessarily runs along these teeth when reverse gear to ensure repeatability \.

A regular rack and pinion arrangement, it is given on the surface or formed by embossing, excludes the possibility of adjusting the friction wheel measuring instrument for accuracy by tilting the wheel As long as the wheel is constrained to follow a track of periodic teeth, it must follow the same Return to the point from which it started, even if the circumference of the wheel is changed slightly, such as when tilting the wheel with a curved peripheral surface happens. If you grind the circumference of an ordinary pinion so that the teeth are only half the height, it will still roll on a rack just like before. The gear ratio is not changed. With regularly arranged teeth, the repeatability is gained by sacrificing the possibility to select a desired one To be able to adjust the burr of accuracy.

In order to obtain accuracy it is important that the measuring wheel get to the origin of its path along exactly the same Returns to the track along which it followed when leaving the origin. From the point of view of repeatability it should follow this track despite minor changes in the tilting of the wheel or changes in the pressure force between the wheel and the measuring surface However, one must be able to provide a completely new track if desired in conjunction with the arbitrary one Edging of the wheel to adjust the accuracy so that a pre-existing track has no influence

309816/0297

Therefore, sharp ridges will appear on the radura muzzle provided, the longitudinal axis of which is transverse to the wheel circumference. The ridges are irregular in contrast to periodically distributed, i.e. the distance between the ridges fluctuates from ridge to ridge irregularly or statistical.

For operation, the measuring instrument is attached to the machine tool in the usual way, the accuracy measured and then adjusted, as required, by using the instrument to change the effective Measuring wheel circumference is folded. If that were all, the jammed wheel would have ridges next to the same Trace that was previously made. The effect would be similar to an ordinary rack and pinion no improved accuracy would be obtained. Therefore, the instrument is disengaged from the before folding Measuring surface brought so that the burrs on the wheel no longer touch the surface »The measuring wheel is in front of the renewed application of the wheel to the measuring surface rotated. The tilt angle of the instrument can either be before or after turning the wheel.

By disengaging the wheel from the measuring surface and turning the wheel can turn the unevenly distributed ridges on it into one before on the Track generated by the measuring surface. Without such a fit, the track along which the measuring wheel will be renewed Feed follows, delete any previous track and create a new track. When the circuit is reversed the burrs on the measuring wheel will follow the new track instead of the old one. This fact becomes the importance the irregular distribution of the ridges. If the ridges were periodically spaced, the Rotation of the wheel while it is disengaged from the

3098 16/0297

The measuring surface has no effect, as the wheel will necessarily intervene again in the old periodic track would if it were brought back onto the plane. The teeth of a pinion mesh with the Teeth of a usual rack * by placing them in the spaces between them fall, regardless of the rotational position of the pinion.

The improved method of adjusting the accuracy of the measuring instrument has only a few steps. First, a six inch long gauge is typically used to match the circumference of the measuring wheel, for example of the commercial instrument TRAV-A-DIAL, English system, coincides. A common dial test pointer is positioned on one of the measuring surfaces of the six inch gauge and zeroed to 0.0001 inch; this happens after the housing was aligned parallel to the X-axis in a known manner. The measuring instrument is also zeroed. The lathe or other machine tool is then advanced exactly six inches so that the dial test pointer points to zero on the second measuring surface of a six inch gauge. Any deviation from what is shown on the Meter of zero (i.e. 6 inches) represents a deviation from accuracy. If the meter indicates more than 6 inches, it means that the measuring instrument must be adjusted so that the tilt angle is reduced. On the other hand, if the meter does not indicate quite six inches, it is necessary to increase the cant angle even further until the measurement is accurate is reached.

Once the size and direction of the measurement error have been recorded, the spring load that the measuring wheel presses against the measuring surface, removed from the measuring device. this

3098 16/0297

however, leaves the measuring wheel still in contact with the measuring surface in a conventional machine tool. The measuring instrument is therefore withdrawn so that the wheel is clear of the measuring surface. The measuring instrument is tilted how this is necessary to improve the accuracy. The scale wheel or display wheel is also turned around rotated an amount that ensures that the same burrs are not again in the same place on the measuring surface be put on. A relatively small rotation of the wheel is sufficient because the ridges are relatively close to one another. That The extent of the displacement should not be equal to an integer number of full revolutions of the wheel, i.e. should be different from a zero revolution or a full revolution. This makes it clear that no more than one effective rotation is necessary and that, if desired, an advance of the retracted measuring instrument relative to the Measuring surface actually causes the same effect of the wheel movement from its earlier track «In practical implementation it is easier to put the wheel on a new part mark. It should also be noted that an important measure the displacement of the wheel circumference is relative to the measuring surface and that this is done by moving the wheel the area can be achieved instead of loosening and readjusting the wheel. This, however, grinds the edges the grade even with hardened wheels and the advantages of the burrs to improve the repeatability are gradually lost. Any kind of displacement between the wheel and the measuring surface can be sufficient to bring about an effective rotation of the wheel «Pulling back and turning has a special advantage.

After the wheel has been rotated relative to the measuring surface, it in turn is brought into engagement with the measuring surface and the spring load is put into action again «Pie Ge—

3 09 8 16/0297

2248799

Accuracy is then measured in exactly the same way and, if necessary, the individual steps are repeated until a desired degree of accuracy is achieved is.

The retraction of the measuring instrument from the measuring surface can be carried out by manipulating the usual fastening device with which the instrument is fastened to the machine. It has been found, however, that once the spring load has been removed from the instrument, it is a very simple matter to manually move the instrument away from the measuring surface, de the flexibility of the attachment and the machine tool allows sufficient deformation so that the Wheel can be rotated freely without it coming into engagement with the measuring surface. In practical implementation, the essential measures therefore consist in loosening the wheel from the measuring surface before the subsequent effective rotation of the wheel and by re-engaging in order to then carry out the measurement. The canting of the measuring instrument for adjusting the accuracy characteristic either before or after resetting of the wheel to happen and can be performed on the In contact property with the measuring face wheel, although it advantageously iat _t that the wheel is detached from the measurement surface · The spring should before be loosened after bending in order to avoid overloading.

As can also be seen from FIGS. A to C, buffers 28 are formed on the instrument housing 10 and are carefully ground parallel to the plane of the measuring wheel 11 . When setting the skew of the measuring instrument is attached to a dial pointer or the like on the lathe bed and adjusted over the buffers · The carriage is then advanced so that the scales

309816/0297

pointer against the other buffer 28 is adjusted by the scale. The skew of the measuring instrument is then adjusted so that the wheel is parallel to the X axis. Was before. the deviation ν on the parallelism of the wheel from the X axis is set to less than about 0.0005 inches, as is that between the two buffers measured about 13/32 of an inch (about 35.72 mm) apart. From this starting point the The skew of the measuring instrument is adjusted so that every repeatability error is eliminated. Typically there are three or four additional adjustments to the slip angle necessary to completely eliminate the repeatability error «,

In the practice of the invention, in which non-uniformly distributed ridges extend across the circumference of the wheel extend, a similar adjustment is used to eliminate the repeatability error; However the initial skew adjustment only needs to be made to only about 0.004 inches, like that is measured between the buffers 28 and it is very common that when an additional skew adjustment is required, such an adjustment is sufficient. This possibility of improved Measuring instrument to compensate for the repeatability error with a skew angle that is about 8 times larger than it used to be, is probably due to the formation of a track by the measuring wheel, which the measuring wheel during the backward stroke follows.

It is desirable to have a high coefficient of friction between the wheel and the measuring surface in the X-direction (circumferential direction) to have the possibility of slippage to press down, which should lead to a measurement error. The burrs that lie against the measuring surface form one of the—

3098 16/0297

like high coefficient of friction. At the same time it is desirable to have one in the Z-direction (transverse direction) to have a relatively low coefficient of friction in order to suppress the coupling effect, which tends to change the canting of the wheel and the pressure force au, both of which contribute to the repeatability error Thus, a high coefficient of friction in the X or circumferential direction improves repeatability and a lower one Coefficient of friction in the Z or cross direction also improves repeatability

The irregularly distributed ridges, the longitudinal axes of which extend in the transverse direction, result in a high Coefficients of friction in the X direction without significant Increase in the coefficient of friction in the Z direction. That the same would not result with depressions or peaks that are uniformly formed on the wheel circumference are how they can be found by sandblasting the circumference or would result from a porous wheel. It has thus, in order to obtain a large ratio between the coefficient of friction in the X direction and the coefficient of friction in the Z direction is the mean Length of ridges. Greater than about three times the mean Distance between the ridges should be. The mean length and the distance are used here in that sense understood that they are a numerical mean without major differences are. A mean let necessary because the actual distance between the ridges is uneven or is statistical. Typical catfish has further been found that when the ridges through Loops are obtained even their length is irregular. The mean length of the ridges is preferably the same five to ten times the mean distance, because this means a large ratio of the coefficients of friction is obtained; this is without major manufacturing problems

3098 16/0297

easy to reach.

Another reason for ridges with a substantial mean length in relation to the mean distance between they can be seen in the fact that it is to be ensured that the wheel is actually in the same track remains despite certain minor changes in the cant angle or translation in the Z direction during a feed. If the burrs were too short, a little canting of the wheel could cause it misses its original track and that again a repeatability error would arise.

It is desirable that the burrs be small and sharp so that a good track is formed and they are used during the Backward thrust does not go off track. The maximum mean distance between the V-shaped ridges on a Wheel circumference is determined by the formula -

2C _for R.
S. -,

where S is the mean distance between the ridges, C _{f is} the coefficient of friction of the measuring wheel material on the measuring surface, R is the radius of the wheel and K is a safety factor. In a typical application where a hardened steel wheel is used on a cast iron or steel part of a machine tool, there can be a coefficient of friction of about 0.2 and the wheel can have a radius of about one inch. If 10 is chosen as the safety factor, a maximum groove spacing of about ^ thousandths of an inch is obtained. This is essentially an absolute maximum; From a practical standpoint, a maximum value of the mean groove spacing of about ten thousandths of an inch is preferable. In a preferred embodiment, the wheel is ground so that the mean

309816/0297

Distance between ridges at about! Thousandths of an inch which results in exceptional accuracy and excellent repeatability without significant manufacturing difficulties. Advantageously, the middle one The burrs are spaced more than about 1 micro-inch as the wheel will be so smooth that there will be no significant increment the ratio of the coefficients of friction is obtained.

It is also important that the burrs are sharp enough to properly grip the measuring surface. When the burrs are sharp, the pressure (force per unit area) of the wheel against the measuring surface is relatively high and a track is formed in the measuring surface. Conventional grinding of the measuring wheel in a direction transverse to its circumference leads to very sharp burrs. The ridges or peaks formed are typically of the same order of magnitude as the crystal size of the metal from which the wheel is made. In a hardened steel wheel preferred in the practice of the invention, an extremely small grain size is typical and grinding produces very sharp, irregularly distributed burrs The edge of the sharpness is essentially that which is produced by grinding with a conventional abrasive grinding wheel. Such sharp edges may slightly abraded during use of the Meßinetrumentes ^11, # 3 but die..noraalt wear can not significantly reduce the usefulness of the instrument.

Any substantial blunting of the ridges, such as the wise in 'polishing, burnishing, electrolytic etching or the like occurs, the usefulness of the The measuring device. Note that such intentional blunting of the sharp ridges, an essential

309316/0297

must have reached a certain size before the instrument no longer works as described above. Thus, by the term "sharp" used to define the ridges, it is expressed that the combs or points remain essentially as they were produced by ordinary grinding, no intentional blunting or smoothing is performed on the ridges or tips of the ridges.

The tips of the ridges not only have to be very narrow, the slope of the ridge sides must also be large. The angle between the slope of the ridges near the ridges and a tangent to the wheel at the tips must be significantly larger than the angle of static friction between the wheel and the surface to be measured (the coefficient of friction between two surfaces is the tangent of the angle of the static friction ). 3 shows the tip of a pair of adjacent ridges 26 which are spaced S apart. The slope Ό between the ridge side and a tangent to the wheel should be significantly larger than the angle of static friction. If this angle is not significantly larger than the angle of static friction, the ridge can slip out of the previously pronounced track. The wheel is preferably hard steel, in any case harder than the measuring surface, so that the burrs are not burnished or blunted even after long use.

Although the invention has been described above in detail with reference to a measuring wheel that is used to adjust the Accuracy of measurement was intentionally rotated spherically, the invention can be applied in the same way to a measuring instrument, in which the circumference of the measuring wheel has the shape of a straight circular cylinder. Such a cylinder area with unevenly distributed sharp ridges that run across

309 8 16/0297

22 * 8789

extend to the circumferential direction of the wheel prevents repeatability errors regardless of the canting technique used to compensate for measurement errors.

In one embodiment of a meter, a wheel has one straight circular cylinder as periphery. If you find that the straight circular cylinder is not quite what you want Or if there is another measurement error, external compensation for this measurement error can be carried out will. Typically, such an instrument has an electronic reading device in which the rotation of the Measuring wheel is determined directly or indirectly by an electronic sensor, for example a photocell. With a suitable, conventional circuit, this rotation of the measuring wheel can be converted into a length or angle measurement in selected units can be transferred without substantial difficulty. Various methods are available for adjustment the displayed measurement is available by the instrument to match the display with the actual distance traveled by the wheel To match length. These techniques distribute the measured deviation from accuracy over the entire measuring length, so that a high accuracy over short or long length measurements or angle measurements is obtained. With such an adjustable electronic reading, a wheel with a right circular cylinder can be used as the periphery in place of the curved periphery described and illustrated above.

Even if the accuracy of the instrument's measurement is electronically calibrated, repeatability errors can occur due to the mechanical hysteresis of the machine tool,., on which the instrument is attached. The unevenly distributed sharp ridges write anyway a track in the measuring surface and thereby prevent reproducibility errors. The fact that the ridges are un-

3098 16/0297

evenly distributed becomes less important if the wheel has a periphery in the form of a right circular cylinder has as if it has a curved periphery, since the measurement errors are electronically compensated and the calibration technology, in which the instrument is detached from the surface and tilted, is not required. The sharpness and substantial length across the circumference of the wheel nevertheless remains of essential importance. The unevenness remains but of some importance since the preferred technique for producing the sharp burrs is conventional grinding provides. This is by far the most economical method of recovering the sharp burrs in the periphery of the wheel. The measuring wheel is preferably hardened steel, ". Allowing the cutting of burrs at regular intervals on the periphery is relatively expensive. If the wheel has sharp transverse burrs before hardening, can the hardening process result in distortion that could generate errors of a small order of magnitude, which cannot easily be compensated for by electronic measures can.

In addition to the above-mentioned deviations, the person skilled in the art is still conceivable of various changes without deviating from the concept on which the invention is based. If, for example, it was mentioned above that the burrs are unevenly distributed, as results from the grinding _s , pseudo-unevenly distributed burrs can also be provided which have a predetermined, non-uniform, aperiodic spacing. Long ridges running across the periphery from side surface to side surface of the wheel are advantageous for practical reasons; however, from other circumstances, shorter burrs can be produced during the grinding process, the length of which is three to ten times the length

309816/0297

mean distance between the ridges.

Overall, measures were taken to reduce the sensitivity of a friction wheel length measuring instrument Skewing described in which several unevenly distributed ridges are provided on the circumference of the wheel, the longitudinal axis of the ridges being transverse to the circumference of the Measuring wheel lies. The length measuring device is advantageously to compensate for accuracy errors adjusted by the fact that the measuring wheel circumference is relative to the measuring wheel Area is adjusted in connection with the setting of a cant angle of the wheel.

309816/0297

Claims (1)

Expectations ί 1 ylength measuring instrument with one along the measuring path rollable measuring wheel and a measuring device for displaying the value of the measuring wheel rotation, characterized in that, that the circumference (23) of the measuring wheel (11) has several irregularly distributed ridges (26), the longitudinal axis of which runs transversely to the circumferential direction of the measuring wheel. 2. Instrument according to claim 1, characterized in that that the mean length of the ridges is greater than about three times the mean distance between the ridges. 3. Instrument according to claim 1 or 2, characterized in that the angle between the slope of the ridges near their crest and a wheel tangent to the Comb is much larger than the static friction angle between the ridge and the measuring path. 4. Instrument according to one of the preceding claims, characterized in that the mean distance between the ridges are less than about 0.010 inches (0.254 mm) from each other. 5. Instrument according to one of the preceding claims, characterized in that the mean distance between the ridges from each other larger than about 10 ~ inches (10 ~ χ 25.4 mm) 6. Instrument according to one of the preceding claims, characterized in that the mean distance between —3 —3 the ridges roughly on the order of 10 inches (10 χ 2 5.4mm). 3098 16/0297 7. Instrument according to one of the preceding claims, characterized in that the burrs from grinding marks are formed by a grinding tool placed essentially parallel to the axis of rotation of the measuring wheel originate. 8. Instrument according to one of the preceding claims, characterized in that the crests of the ridges substantially have the sharpness produced by grinding 9. Instrument according to one of the preceding claims, characterized in that the peripheral surface (23) of the measuring wheel, that bears the ridges is curved. 10. Instrument according to one of claims 1 to 8, characterized in that the circumferential surface of the wheel which the Bears ridges, has the shape of a straight circular cylinder 11. Instrument according to one of the preceding claims, characterized in that the irregularly distributed Burr the coefficient of friction of the wheel in the circumferential direction and do not significantly increase the coefficient of friction of the wheel transversely to the circumferential direction. 12. Procedure for adjusting the accuracy of a length measuring instrument with a frictional connection over the Meßweq rollable Keßrad, characterized in that the measuring wheel circumference and the measuring path are displaced relative to one another and adjusted for greater accuracy. 13. The method according to claim 12, characterized in Dais shifting disengagement of the wheel from engagement with the measure path and rotation of the wheel relative qelösten 0 9 8 16/0297 to the measuring path includes. 14, the method according to claim 12 or 13, characterized in that the shifting a retraction of the Wheel out of engagement with the measuring path and a translation of the retracted wheel relative to the measuring path includes. '15. Method according to Claim 12 or 13, characterized in that the shifting comprises withdrawing the wheel from engagement with the measuring path \ vc \ a rotating the wheel about its axis. 16. The method according to any one of claims 12-15, characterized in that the adjustment for accuracy comprises a folding of the measuring wheel relative to the measuring path. 1670297 3 «* Blank page