CN204404992U - High-precision flat face measuring apparatus - Google Patents

Abstract

The utility model relates to a measuring instrument, in particular to a high-precision plane measuring instrument for measuring a circular knife, comprising a measuring plate, a measuring device located on the measuring plate, and a bracket for supporting the measuring plate. The measuring device includes a Three positioning points protruding from the measuring plate on the measuring reference plane, a circular knife positioning screw with a supporting bearing, and a measuring point set on the center line of the measuring plate, wherein the positioning screw is detachably installed At the bottom of the measuring plate, the supporting bearing is used to support the outer circle of the measured circular knife; the three positioning points protruding from the measuring plate are also used to support the measured circular knife; among the three positioning points , one is a fixed point, which is located at the bottom of the center line of the measuring board and the upper part of the positioning screw; the other two positioning points are moving points. The utility model has the advantages of simple structure, improved measurement efficiency and accuracy, and the like.

Description

High precision plane measuring instrument

technical field

The utility model relates to a measuring instrument, in particular to a high-precision plane measuring instrument for measuring the thickness, flatness and parallelism errors of circular knives used for cutting metal thin plates.

Background technique

The applicant's existing patent ZL2010101106005 discloses a plane accuracy measuring instrument for measuring thickness, flatness and parallelism errors, which can accurately measure the thickness, flatness and parallelism errors of the measured workpiece. The plane accuracy measuring instrument includes a measuring board and a measuring device located on the measuring board, a bracket for supporting the measuring board is arranged under the measuring board, and at least three not in a straight line and protruding from the measuring board are arranged on the measuring board. Support protrusions on the upper surface. Since three points that are not on a straight line can determine a plane, any three support protrusions protruding from the upper surface of the measuring plate form a support plane for supporting the measured circular knife and related tools, and with this support The plane is used as the reference, which can accurately obtain the thickness of the workpiece to be measured, the thickness error of the same circular knife (parallelism error) and flatness error, which is not affected by whether the measuring board is flat or not, which can greatly improve the measurement accuracy, especially suitable for It is widely used on measuring devices for measuring thickness, parallelism and flatness errors of similar parts.

During the use in the past five years, the applicant has found some shortcomings in the original patent one after another, and hopes to make improvements. For example: the measurement of flatness in the original patent is to use a dial gauge. But the dial indicator is not accurate, its scale is too dense, the pointer is too short, it swings by the pointer, and the minimum scale of 1μ (is) is read by the naked eye, and the reading error is relatively large. Another example is in the original patent, there is a special mechanism in the measuring instrument, that is, three points pass through the slider, and the three points are moved synchronously along their respective radial directions by means of the plane spiral groove, so as to measure the three points when they move in the radial direction. , the height change of the midpoint between two points. However, this structure is very complicated and difficult to manufacture, and the slider moves by dynamic cooperation, so it is not fixed during measurement, its rigidity and stability are not good, and its operation is inconvenient.

At the same time, another published patent document CN1851386A relates to a flatness tester for the glass substrate of a circular optical disc master disk, which includes: a triangular worktable, three circular seats are respectively arranged on the triangular worktable, A round steel ball is placed on each round seat; at the triangular position on the edge of the triangular worktable, a group of small ball bearings are evenly distributed with fixed seats; below the center hole of the triangular worktable, a A dial gauge; it overcomes the unfavorable factors that affect the measurement accuracy due to the deformation of the substrate of the circular disc master disc of various specifications due to the weight of the glass, so that the measurement accuracy is greatly improved, reaching 0.001mm, especially suitable for common large areas (such as φ160 ~φ240mm) ultra-thin and easily deformable circular disc master glass substrate (outer diameter/thickness=10:1～200:1).

For reasons already stated by the applicant, although such a design is an improvement over conventional measurement methods of the past, it still leaves room for many further improvements. For example: using a dial indicator, the highest reading accuracy is 0.001 mm, which may not be able to meet the accuracy requirements in actual work. Simultaneously, the described "a rotatable small steel ball is installed on each circular seat" disclosed in this published document also increases the error of the steel ball diameter itself produced when the steel ball rolls. In addition, since this public document is used for measuring the glass substrate of a circular optical disc master, it is a device placed on a plane, relying on three small bearings to fix the outer circle, which is inconvenient for adjustment. For another example, its discs of the technology disclosed in this patent are adjusted in stages, which is also inconvenient during operation.

At present, the applicant hopes to provide new methods and ideas for the shortcomings of the above-mentioned existing technologies, and continue to improve the technical measurement technology of the plane measuring instrument.

Utility model content

The utility model aims to provide a high-precision plane measuring instrument, which can obtain more accurate measurement of flatness and parallelism, is simple and convenient to use, and is suitable for circular knives with different diameters.

In order to achieve the above-mentioned purpose of the invention, the technical solution provided by the utility model is:

A high-precision plane measuring instrument is used for measuring round knives, including a measuring board and a measuring device located on the measuring board, and a bracket arranged under the measuring board to support the measuring board, and the measuring device includes three a positioning point protruding from the measuring plate, a positioning screw with a support bearing circular knife, a measuring point of a high-precision inductance micrometer sensor arranged on the center line of the measuring plate, wherein the positioning screw is It can be detachably installed on the bottom of the measuring board, and the supporting bearing is used to support the outer circle of the measured round knife; the three positioning points protruding from the measuring board are used to support the measured round knife on the one hand, and the other On the one hand, for the principle of determining a plane by three points, the three positioning points can form a measurement reference plane; among the three positioning points, one is a fixed point, which is located at the bottom of the centerline of the measuring board, positioned The upper part of the screw rod; the remaining two positioning points are moving points; an auxiliary measuring instrument bracket is also provided on the column of the measuring plate, and the measuring instrument bracket is also used for installing an external sensor to measure the thickness and parallelism of the circular blade.

On the basis of the above scheme, the three positioning points all include a support block and hard alloy steel balls protruding from the support block; wherein, the support block of the fixed point is fixed at the center line of the measuring plate The bottom, the top of the positioning screw; the supporting blocks of the two moving points are arranged in the two inclined positioning grooves on the surface of the measuring board, and the moving points can slide along the inclined positioning grooves, and the inclined positioning grooves are The above-mentioned fixed point is the origin, and the chute is provided on both sides of the centerline of the panel passing through the center of the fixed-point steel ball; the angle between the above-mentioned oblique positioning groove and the centerline of the measuring plate is 30°; that is, the three The anchor points form the three vertices of an inverted equilateral triangle. Trace it to its design reason, be because the accuracy of measuring the middle point of any two points of them is the highest when the distance between three positioning points is the farthest from each other, and here it is the equilateral triangle of the inscribed circle that just can reach this requirement. Because one of the three anchor points is fixed and is fixed in the middle of the lower end of the measuring panel, the equilateral triangle is inverted. Moreover, when the outer circle at the lower end of a round knife is placed on a fixed point, as the outer circle increases and shrinks, the moving tracks of the two moving points of the inverted equilateral triangle are just at the point where the two moving points are 30 degrees from the center line. degree chute.

The hard alloy steel ball cannot rotate relative to the support block. Specifically, no matter whether the cemented carbide steel ball is fixed or adjustable, it cannot rotate, which avoids the possibility of bringing in the diameter error and garbage of the steel ball itself and affecting the measurement accuracy.

The measuring point is a sensor measuring point of an external precision inductance micrometer, which is measured by a measuring head installed on the measuring point; the measuring head is connected to the external precision inductance micrometer body through a cable; the measuring point Set in the measuring groove coincident with the center line of the measuring plate, it can slide along the measuring groove. There is a scale next to the measuring groove, and the position of the measuring point can be determined according to the size of the round knife and the scale outside the groove. In actual use, the position of the measuring head can not only slide along the measuring groove, but also fine-tune up and down in its axial direction, so as to withstand the lower plane of the circular blade to be measured. The measuring range of the sensor is one millimeter, and it can use a very light spring force to push the measuring head on the lower plane that has been positioned on the measured circular knife. This extremely light spring force, which cannot be compared with the weight of the blade, will not interfere with the measurement results. Such a measurement method makes the measured plane of the circular blade completely coincide with its reference plane, and eliminates the interference of the blade thickness error on the flatness.

The positioning screw is a screw with left and right threads; a slider is respectively connected to the left and right threads of the screw, and the bottom surface of the slider is close to the measuring plate, so that the slider can only move along the screw; Each slide block is equipped with a bearing to move together with the slide block, and the bearing is used to support the outer circle of the measured circular knife.

The positioning screw is also connected with a hand wheel, and when the hand wheel is turned, the bearings on the slider will move closer to or move away from the center of the screw synchronously.

Both the fixed positioning point and the center of the positioning screw are located on the center line of the measuring board.

The reading accuracy of the inductance micrometer is not less than 0.1μ. Specifically, the reading accuracy of the meters used in the workshop can reach 0.1μ, while the digital meters used in the measurement room appraisal can reach 0.01μ.

The measuring board forms an included angle of 30° with the horizontal plane. After being placed in this way, the circular blade to be tested will use its small self-weight component force to make its outer circle close to the outer circle of the bearing. And because of the symmetry of the bearing position, one diameter of the circular knife to be tested can always coincide with the centerline of the measuring plate.

In addition to the advantages that have been set forth above, compared with the prior art, the utility model has the following advantages:

(1) Replace the dial indicator with an inductance micrometer to make the reading more accurate and reduce the reading error;

(2) The measurement point of the sensor is on the datum plane determined by the three positioning points, which makes the measurement flatness simple and improves the measurement efficiency;

(3) The positioning screw is a double-bearing positioning structure, which makes the operator easy, efficient and accurate in use;

(4) Use the positioning screw to steplessly adjust the position of the fixed round knife to adapt to the measurement of different diameter round knives;

(5) Using this technology to measure, the operation is simpler, faster and more accurate.

Description of drawings

Accompanying drawing 1 is panel layout drawing of the present utility model;

Accompanying drawing 2 is a side view of the utility model;

Accompanying drawing 3 is the structural representation of positioning screw in the utility model;

Accompanying drawing 4 is the layout schematic diagram of three reference points of the measuring instrument of the present invention.

Explanation of the numbers in the accompanying drawings:

1 - measuring board;

2 - bracket;

30——datum; 31——fixed point;

32, 33 - moving point; 320, 330 - moving track of moving point;

34——measuring point; 341——measuring head slide;

342——measuring head; 343——external cable;

311, 312, 313 - support blocks;

321, 322, 323 - steel balls;

35 - positioning screw;

351——left thread; 352——right thread;

353, 354——slider; 355, 356——slider bearing;

357—hand wheel;

3581, 3582 - screw support;

359 - connecting rod;

36——Measuring board center line;

371, 372——oblique positioning groove; 38——measuring groove;

4——Inductance micrometer;

5——Measuring instrument bracket; 51——Meter frame; 52——Sensor connection hole;

6 - round knife;

71,72——spare bearing holes.

Detailed ways

Please further illustrate the utility model below in conjunction with the accompanying drawings of the description.

As shown in accompanying drawing 1 and accompanying drawing 2, high-accuracy plane measuring instrument comprises measuring board 1 and is positioned at the measuring device on measuring board 1, described measuring board 1 is provided with support 2 for supporting measuring board, described The measuring device includes three positioning points protruding from the measuring plate constituting the measuring reference plane 30, a positioning screw 35 with a support bearing, and a high-precision inductance micrometer sensor measuring point 34 arranged on the center line of the measuring plate , wherein, the positioning screw 35 is installed on the lower end of the measuring plate 1 through the screw support 3581, 3582, and is used to support the outer circle of the measured circular knife 6; the three positioning points protruding from the measuring plate are also Used to support the outer circle of the measured circular knife 6; among the three positioning points, one is a fixed point 31, and the remaining two are moving points 32, 33; the fixed point 31 is located at the bottom of the centerline 36 of the measuring plate , the top of the positioning screw 35. The other two positioning points are moving points 32 , 33 , and the moving points 32 , 33 can slide along the inclined positioning grooves 371 , 372 .

As shown in accompanying drawing 1 and accompanying drawing 4, specifically, the oblique positioning grooves 371, 372 take the fixed point 31 as the origin, and are opened on both sides of the center line 36 of the measuring plate passing through the center of the fixed point steel ball 321. Inclined groove; the included angle of above-mentioned oblique positioning groove 371,372 and measuring plate centerline 36 all forms 30 ° (as in accompanying drawing 4, moving point moving track 320,330 is the measuring position of oblique positioning groove 371,372, moving point The two 30° included angles formed by the moving tracks 320, 330 and the center line 36 of the measuring plate are the angles formed by the oblique positioning grooves 371, 372 and the center line 36 of the measuring plate); particularly as shown in Figure 4, the three The three positioning points form the three vertices of an inverted equilateral triangle inscribed in the outer circle of the circular knife to be tested. For example, the three vertices of the inscribed equilateral triangle of the Φ160 circular knife in the figure are the fixed point 31, point A and point B. ; The three vertices of the inscribed regular triangle of the Φ240 round knife are fixed points 31, A1 and B1; the three vertices of the inscribed regular triangle of the Φ300 round knife are fixed points 31, A2 and B2. No matter how the diameter changes, the fixed point 31 will always be a vertex of an equilateral triangle inscribed on the circular knife.

An auxiliary measuring instrument support 5 is also arranged on the measuring board, and a sensor can be installed to measure the parallelism and thickness of the circular knife. As shown in Figure 2, the measuring instrument bracket 5 is equipped with a meter frame 51 that can move up and down along the measuring instrument bracket 5, and the meter frame 51 can be equipped with a measuring meter such as a micrometer, and the measuring sensor can pass through the sensor connecting hole 52 Place it so that the measured circular knife 6 can be measured from above the measuring board. The specific measurement method will be described in detail below.

On the basis of the above solution, each of the positioning points includes a support block and hard alloy steel balls protruding from the support block. Specifically, the fixed point 31 includes a support block 311 and a hard alloy steel ball 321 protruding from the support block 311; the moving point 32 includes a support block 312 and a hard alloy steel ball 322 protruding from the support block 312; the moving point 33 It includes a support block 313 and a cemented carbide steel ball 323 protruding from the support block 313 .

Wherein, the supporting block 311 of the fixed point 31 can be fixed on the measuring plate 1 by screws; the center line 36 of the measuring plate passes through the center of the hard alloy steel ball 321 of the fixed point, at the upper end of the measuring plate center line 36 Set measuring groove 38 (also can be referred to as: measuring instrument sensor groove), be used for positioning measuring point, this measuring point can move in measuring groove 38 and locate according to groove edge scale; Then take described fixed point as origin, in measuring The 30° directions on both sides of the center line of the plate are respectively provided with oblique positioning grooves 371, 372 of equal length; the supporting blocks 322, 323 of the two moving points 32, 33 move and press in the two oblique positioning grooves 371, 372 respectively. Groove edge scale positioning. The measuring board 1 can also be marked with a scale, so that when the circular knife is measured, the positioning point can slide to an appropriate position.

The principle of the above design is:

To support the three positioning points forming the measuring datum surface 30 of the circular knife, the maximum distance between them is to be obtained, which is the inscribed equilateral triangle of the outer circle of the blade. When the lower end of each circular knife is placed on the fixed point 31 of the positioning point, and the other two moving points 32, 33 need to be adjusted for measuring different diameter cutters, their tracks are starting from the fixed point and moving along the center line 30 ° straight line. Therefore, the direction of the positioning groove is 30° to the centerline, and the angle between the two oblique positioning grooves is 60°, and the measuring groove 38 located on the centerline of the measuring plate is specially set for the sensor measuring point.

When the diameter of the round cutters changes, the other two points A and B on their inscribed inverted triangles always extend along the direction of 30 degrees from the fixed point to the center line of the panel. Therefore, as long as two 30-degree oblique lines are slotted, two movable points can be used to adapt to blades of different diameters, thereby greatly simplifying the structure of the measuring panel. In order to improve the measurement accuracy, the distance between the three positioning points should be the largest, and such an arrangement can only meet the requirement of a regular triangle inscribed in a circle. Based on the above considerations, the three positioning points in this scheme design are are the three vertices of an inverted equilateral triangle.

On the basis of the above scheme, the sensor measuring head 342 is installed in the measuring head sliding seat 341, and the measuring head sliding seat 341 can slide along the measuring groove. 4 (not shown in the figure) is connected to display the value of the thickness, flatness and flatness of the round knife measured on the reference plane. With such a design, it will neither entangle the parallelism errors of the blades when using a marble plate to measure the flatness of the round knife as is commonly used in China, nor will it require sampling like some existing high-end roundness meters. Thousands of points are used to find the datum plane where the measured flatness is not disturbed by the parallelism of the circular knife.

Based on the above solution, the cemented carbide steel balls 321 , 322 , 323 cannot rotate relative to the support blocks 311 , 312 , 313 . In actual use, the wear caused by the movement of the measured round knife on the cemented carbide ball is negligible and completely negligible in the process of completing the measurement of a piece of blade.

In order to adapt to different blade diameters, the positions of the support blocks 312, 313 can be adjusted, but the support blocks 312, 313 are locked during measurement and cannot slide freely, so that the measurement system has good rigidity. Therefore, the measurement accuracy and reliability are greatly improved.

Specifically, as shown in accompanying drawings 1 and 3, the positioning screw 35 is a symmetrical screw with a left thread 351 and a right thread 352; a slider 353 is provided on each of the left and right threads of the screw , 354, slide blocks 353, 354 are arranged symmetrically along the center line 36 of the measuring plate, and the bottom of the slide block 353, 354 is close to the measuring plate, so that the slide block 353, 354 can only move along the positioning screw 35; the slide block A sliding block bearing 355,356 is respectively adorned on 353,354, and this sliding block bearing 355,356 moves together with described sliding block 353,354.

On the basis of the above solution, the screw supports 3581 , 3582 are connected to the measuring plate, and the screw supports 3581 , 3582 are detachably fixed on both sides of the measuring plate and connected by a connecting rod 359 . If the diameter of the measured circular blade is too large, the connecting rod 359 and the screw supports 3581, 3582 on both sides can also move downwards, and the two bearings 355, 356 supporting the outer circle of the circular blade can be adjusted to the slider 353 , 354 below the spare bearing holes 71,72.

On the basis of the above scheme, the positioning screw 35 is also connected with a handwheel 357. When the handwheel 357 is turned, the bearings 355, 356 on the sliders 353, 354 will move towards or away from each other synchronously with the center of the screw. .

On the basis of the above solution, the centers of the fixed positioning point 31 and the positioning screw 35 are both located on the centerline of the measuring plate. To ensure that the slider bearings 355, 356 are arranged symmetrically according to the centerline 36 of the measuring plate, the purpose is to ensure that the three positioning points are the three apexes of the inscribed inverted equilateral triangle of the measured circular knife.

On the basis of the above scheme, the measuring point is externally connected with an inductance micrometer 4 . The reading accuracy of the inductance micrometer 4 is not less than 0.1μ. For this inductance micrometer, two different models can be used: one is: pointer type, the reading accuracy is 0.1μ, and the other is digital type, the reading accuracy is 0.01μ. The former is used for on-site measurement in the factory, and the latter is used for final qualification measurement in the metering room. Due to the accurate readings, good results can be achieved in practical work.

The measuring board forms an oblique angle of 30° with the horizontal plane. As shown in Figure 2, at the position of the 30° oblique angle formed by the measuring board 1 and the horizontal plane, the measured circular knife is placed on the positioning point by its own weight, and the measured circular knife is naturally moved downward through its self-weight component force. The outer circle of the circular knife rests on the two slider bearings; at the same time, the positions of the two slider bearings can be adjusted freely to obtain the most stable support for the tested circular knife. The bevel angle of 30° is not the only option for this application, as long as it can support the round knife 6 and lean against the slider bearings 355, 356 by the self-weight of the round knife, any angle can be used in this application.

The installation method of the measured circular knife is very simple:

In order to adapt to the measurement of blades with different diameters conveniently, the positions of two movable positioning points and one measuring point can be determined according to the diameter of the circular blade and the positioning groove on the measuring plate, and the scale next to the measuring groove, and their sliders are fixed. Then round knife 6 is put on three positioning points, and blade can move down because of its own weight, leans against on the sliding block bearing 355,356 of positioning screw rod 35, at this moment as long as shake hand wheel, adjust two sliding bearings 355, 356 distance until the outer circle of the bearing can lean against the outer circle of the round knife, and then make some fine adjustments to make the blade reach the best supporting position. If the diameter of the round knife (knife) is too large or too small, and the distance of the bearings cannot be adapted, the supports 3581 and 3582 at both ends of the positioning screw can also be adjusted up and down along the measuring plate 1, and the two bearings can also be moved. On the spare bearing hole 71,72 below the slide seat, to adapt to the needs of various diameter blades.

The utility model has at least the following measurement methods:

(1) The circumferential flatness and radial flatness of the circular knife are combined to give the full flatness

As mentioned above, use the measuring point of the sensor located in the measuring groove 38 to measure (that is, measure through the reference plane 30), the apex of the measurement point is on the datum plane formed by the vertices of the three positioning points, when the rotation When the circular knife is used, the measuring point of the sensor will move slightly up and down. This micromomentum is the measured value displayed by the external inductance micrometer, that is, the circumferential flatness of the plane measured by the circular knife.

In addition, when the hand wheel is turned, the two slider bearings on the screw rod will approach or move away from each other. At that time, the blade leaning on the bearing will move along the center line due to the bearing getting closer, or leave and move down. Thereby the purpose of letting the blade slide over the sensor to measure its radial flatness is achieved. But at this time, the two movable positioning points should be adjusted to ensure that the blade will not fall when it moves radially.

(2) Parallelism of circular knife

Repeat the method of measuring the flatness, adjust the positions of the three positioning points according to the outer diameter of the circular blade, and place the sensor of the inductance micrometer on the measuring instrument bracket (that is, install the sensor through the sensor connection hole 52 of the measuring instrument bracket to measure ), use the lower part of the round knife to jack up the measuring head of the sensor, and place it on the three positioning points, and then adjust the positions of the two supporting bearings. After everything is installed, start to adjust the relative position of the measuring head of the sensor of the inductance micrometer to the surface of the circular knife to be measured, so as to minimize the measuring force. By rotating the circular knife, the difference between the measured maximum and minimum data is the thickness difference of each blade, that is, the parallelism of the circular blade.

(3) The thickness of the round knife

In the prior art, the distance between the measuring head of the sensor and the reference plane composed of the three positioning points can be directly calibrated by using a measuring block gauge (that is, a block gauge), but the use of a block gauge on a fixed positioning point cannot guarantee Whether it is parallel to the datum plane or not, so only a piece of round knife can be used to achieve the purpose of calibration, because after the round knife is placed on the three positioning points, the upper plane of the round knife is basically parallel to the datum plane, because the two sides of the round knife are not parallel The thickness measurement error caused by the thickness is twice as small as it is completely negligible.

In this measurement method, the installation method of the sensor measuring head is consistent with the parallelism of the circular knife.

The specific method of measuring the thickness of the round knife is: find a blade with better parallelism and flatness from the tested round knife, and then use the block gauge of the same thickness and the high-precision digital display micrometer card to repeatedly compare the block gauge and the The thickness of this round knife at a certain point, and determine the thickness of this round knife as the standard thickness for future measurement. Then according to the aforementioned method, this circular knife is placed on the reference plane 30 of the measuring instrument, and then the "zero position" of the inductance micrometer is adjusted to the measured thickness of this circular knife. If you want to measure the thickness of other round knives, insert the outer circle of the lower part of the round knives between the measuring head of the sensor and the fixed point steel ball 321, and then place the whole round knives to be measured on the reference plane 30 for three-point positioning. Move down circular knife, allow tested circular knife to lean on sliding bearing 355,356. The correcting offset read at this time is the thickness difference between the measured circular knife and the standard circular knife. Adding and subtracting this deviation on the basis of the thickness of the standard circular knife is the actual thickness of the measured circular knife.

Claims (9)

1. A high-precision plane measuring instrument is used to measure round knives, comprising a measuring board and a measuring device positioned on the measuring board, and a support for supporting the measuring board being located at the bottom of the measuring board, wherein the measuring device includes Three positioning points protruding from the measuring plate, a circular knife positioning screw with a support bearing, and a measuring point of a high-precision inductance micrometer sensor arranged on the center line of the measuring plate constitute the measuring reference plane, wherein, The positioning screw is detachably mounted on the bottom of the measuring plate, and the supporting bearing is used to support the outer circle of the measured circular knife; The three positioning points protruding from the measuring plate are also used to support the measured circular knife. Among the three positioning points, one is a fixed point, which is located at the bottom of the center line of the measuring plate and the upper part of the positioning screw. The remaining two anchor points are moving points; An auxiliary measuring instrument support is also arranged on the column of the measuring plate, and the measuring instrument support is also used for installing external sensors. 2. The high-precision plane measuring instrument according to claim 1, wherein the three positioning points all include a support block and hard alloy steel balls protruding from the support block; wherein, The support block of the fixed point is fixed at the bottom of the center line of the measuring plate and the upper part of the positioning screw; The supporting blocks of the two moving points are arranged in two inclined positioning grooves on the surface of the measuring board, and the moving points can slide along the inclined positioning grooves, which are based on the above-mentioned fixed point as the origin. Chutes provided on both sides of the centerline of the panel passing through the center of the steel ball at the fixed point; The included angles between the oblique positioning grooves and the center line of the measuring plate are respectively 30°; that is, the three positioning points form three vertices of an inverted equilateral triangle. 3. The high-precision plane measuring instrument according to claim 2, wherein the hard alloy steel ball cannot rotate relative to the support block. 4. The high-precision plane measuring instrument according to claim 1, wherein the measuring point is a sensor measuring point of an external precision inductance micrometer, and is measured by a measuring head installed on the measuring point; The measuring head is connected with the body of the external precision inductance micrometer through a cable; the measuring point is set in the measuring groove coincident with the center line of the measuring plate, and can slide along the measuring groove. 5. The high-precision plane measuring instrument according to claim 1, wherein the positioning screw is a screw with left and right threads; a slider is respectively connected to the left and right threads of the screw, and the bottom surface of the slider is Close to the measuring plate, so that the slider only moves along the screw rod; each of the sliders is equipped with a bearing to move together with the slider, and the bearing is used to support the outer circle of the measured circular knife. 6. The high-precision plane measuring instrument according to claim 5, wherein the positioning screw is also connected with a hand wheel, and when the hand wheel is turned, the bearing on the slider will move closer to the center of the screw synchronously or opposite movement. 7. The high-precision plane measuring instrument according to claim 2 or 6, characterized in that, the center of the fixed positioning point and the positioning screw are both located on the center line of the measuring plate. 8. The high-precision plane measuring instrument according to claim 1, characterized in that, the reading accuracy of the inductance micrometer is not less than 0.1 μ. 9. The high-precision plane measuring instrument according to claim 1, characterized in that, the measuring board forms an included angle of 30° with the horizontal plane.