JPH057144B2 - - Google Patents

Description

[Detailed Description of the Invention] A. Object of the Invention Industrial Application Field The present invention relates to a surface polishing method and apparatus, and more specifically, a constant pressure polishing method for a workpiece surface in a numerically controlled machine tool connected to a computer. and equipment.

Conventional technology When manufacturing a workpiece with a free-form surface, such as a mold, first rough finishing is performed using a machine tool such as a copy milling machine or machining center, and then smoothing is performed using a hand tool such as a hand grinder, so-called final polishing. It is common to apply For rough finishing, highly automated numerically controlled machine tools and copying machine tools are used, allowing extremely highly efficient automatic machining. However, the reality is that final polishing relies on manual finishing using hand tools, and it has been recognized that this is an obstacle that cannot be overlooked when trying to automate the polishing process and improve the dimensional accuracy of the workpiece. .

In order to achieve automation of such a polishing process, various measures have been proposed so far. As an example, a method is known in which a grindstone is attached to the main shaft of a machining center and the surface of the workpiece is polished by rotation of the main shaft. However, in this method, the locus of movement of the grinding wheel rotation axis is defined in the workpiece machining program that is input into the computer in advance, and simply moving the grinding wheel according to the machining program is insufficient for polishing with sufficient dimensional accuracy. The reality is that you cannot get a face.

Problems to be Solved by the Invention The following factors can be cited as reasons why practically sufficient dimensional accuracy cannot be obtained in polishing the surface of a workpiece using the above-mentioned numerically controlled machine tool.

Grinding wheels generally have lower rigidity than cutting tools, and moreover, the amount of grinding that a grinding wheel can do is an order of magnitude greater. For this reason, even if the polishing tool is given the same movement locus as the cutting tool, it often ends up in an empty polishing state due to polishing of the grindstone and changes in shape.

Chips are discharged from the polishing surface by moving the grindstone surface and the workpiece relative to each other while applying a predetermined contact pressure between the two. In order to maintain this chip evacuation function, it is necessary to maintain the contact pressure between the surface of the grindstone and the workpiece at a constant level. However, the grindstone itself is an elastic body, and the shape of the grindstone changes irregularly as the grindstone wears. The purpose of the final polishing process is to improve the surface roughness while maintaining as much as possible the dimensional accuracy of the workpiece obtained in the rough finishing process, and for this purpose, the above contact pressure must always be maintained at a constant level. This is a necessary condition. However, when polishing a free-form surface of a workpiece using a conventional numerically controlled machine tool, the contact pressure between the workpiece and the grinding wheel changes over time as the grinding wheel wears, and as a result, the dimensional accuracy of the workpiece changes over time. was severely impaired.

A main object of the present invention is to provide a surface polishing method and apparatus which can solve the above-mentioned problems observed in the known methods of polishing the surface of a workpiece using a numerically controlled machine tool.

Another main object of the present invention is to provide a numerical control device with an additional tracing function that can automatically correct the movement trajectory of the grindstone based on the displacement detection signal of the grindstone rotation axis transmitted from the constant pressure polishing head. The object of the present invention is to provide a surface polishing device with improved surface polishing properties.

(b) Means for Solving the Problems in the Structure of the Invention The present invention provides a method for polishing the surface of a workpiece using a constant pressure polishing head tool attached to the main shaft of a numerically controlled machine tool. The elastic displacement of the grinding wheel rotation shaft in the X-axis, Y-axis, and Z-axis directions due to contact with the workpiece is detected as the amount of displacement in the axial direction of the grinding wheel rotation shaft, and the detected displacement amount is sent to a computer. The first gist is a surface polishing method in which the workpiece surface is polished at a constant pressure by moving the grindstone while correcting the movement locus of the grindstone rotation axis by adding or subtracting command values from a workpiece machining program input in advance. be.

The present invention also provides a floating support mechanism that supports a grinding wheel rotation shaft of a constant pressure polishing head mounted on the main shaft of a numerically controlled machine tool so as to be elastically displaceable with respect to the constant pressure polishing head, and axis, and Z
a detection mechanism that detects each elastic displacement in the axial direction as an electrical signal representing the amount of displacement in the axial direction of the grinding wheel rotating shaft; and a workpiece machining device connected to the numerically controlled machine tool and into which the amount of displacement according to the detection signal is input in advance. The second aspect is a surface polishing apparatus in which a constant pressure polishing mechanism is formed by a computer that corrects the command value of a program by adding or subtracting it.

Embodiment The basis of the present invention is a general-purpose numerically controlled machine tool,
For example, a constant pressure polishing head 1 equipped with a built-in device for detecting the polishing resistance acting on the grinding wheel rotating shaft 2 is attached to the main shaft 26 of a machining center, and the constant pressure polishing head 1 is adjusted in accordance with a numerical control program preset as a workpiece machining program. The surface of the workpiece is polished while automatically correcting the movement trajectory according to the elastic displacement detection signal from the detection device.

FIG. 1 is a partial longitudinal cross-sectional view illustrating the main structure of a surface polishing apparatus according to the present invention, and FIG. 2 is a schematic explanatory diagram of the method of the present invention.

In FIG. 1, reference numeral 1 designates a constant pressure polishing head. The constant pressure polishing head 1 has a tool shank (not shown) connected to a main shaft 26 of a numerically controlled machine tool.
By manufacturing it in accordance with the shape of the machine, it can be installed in any numerically controlled machine tool that has the same spindle structure. Inside the constant pressure polishing head 1, a grindstone rotating shaft 2 of, for example, an air motor type (vane type) is floatingly supported so as to be elastically displaceable in the X-axis, Y-axis, and Z-axis directions. An air introduction port 3 is provided at the base end of the grinding wheel rotation shaft for introducing high-pressure compressed air supplied from a compressed air source outside the system into the inside of the grinding wheel rotation shaft and rotating the grinding wheel 4 at high speed. . A flange 5 extending perpendicularly to the axis of the whetstone rotation shaft 2 is provided on the side body of the whetstone rotation shaft 2, and a conical shape is formed at the base end of the flange on the whetstone 4 side over its entire circumference. A pressure receiving surface 6 having a shape is formed. A plurality of steel balls 8a arranged so as to be positioned on the same circumference within the holder 7 are arranged opposite to the steel balls 8a with the flange 5 in between.
b, and the flange 5 is sandwiched therebetween, forming a part of the floating support mechanism S of the grindstone rotating shaft 2.
That is, by floatingly supporting the flange 5 by the opposed steel balls 8a and 8b, the grindstone rotating shaft 2 is allowed to freely elastically displace within the XY plane. On the other hand, a retainer 10 is attached to the holder 7 as a holding member for the steel balls 9 urged by a coil spring 11. Steel ball 9 biased by coil spring 11
The rest of the floating support mechanism S of the grindstone rotation shaft 2 works together with the second coil spring 13 described later and the holder 7 so as to apply a pressing force in the negative direction of the Z axis to the conical pressure receiving surface 6. It forms part of the Therefore, the grindstone rotating shaft 2 is constantly pressed in the negative direction of the Z-axis by the compression reaction force of the coil spring 11 and the steel ball 9, and has a self-restoring function that allows it to automatically return to a mechanically stable zero point. It is being When the grindstone 4 contacts the workpiece W during polishing and a reaction force of the polishing load is applied, the pressure receiving surface 6
The steel ball 9 and the coil spring 11 are elastically displaced within the XY plane, and as a result of the elastic displacement, the steel ball 9 and the coil spring 11 are compressed and moved in the positive direction of the Z axis. In this way, a movement resistance uniquely defined by the inclination angle of the conical pressure receiving surface 6 and the compression reaction force of the coil spring 11 is generated on the grindstone rotating shaft 2 .

Further, the holder 7 is supported by a linear guide element 12 such as a ball slide so as to be linearly movable in the Z-axis direction, and is constantly pressed in the positive direction of the Z-axis by a coil spring 13. Therefore, grindstone 4
When a contact reaction force occurs in the negative direction of the Z-axis, the entire grindstone rotating shaft 2 is guided by the linear guide element 12 and retreats in the negative direction of the Z-axis. As can be understood from the above explanation, the grinding wheel rotating shaft 2 has a self-restoring property that automatically returns to a mechanically stable zero position when a polishing load is applied, and moreover, It is configured so that it can be elastically displaced in any direction depending on the size.
Furthermore, since a reaction force proportional to the amount of deflection is generated in the coil springs 11 and 13, a proportional relative relationship is established between the polishing load applied to the grindstone 4 and the elastic displacement generated in the grindstone rotating shaft 2. ing.

In this way, the polishing resistance applied to the whetstone rotating shaft 2 is
Since it is detected as the elastic displacement of the grinding wheel rotation axis,
By transmitting the elastic displacement to the workpiece machining program that has been input into the computer in advance as a parameter for modifying the movement trajectory of the grinding wheel rotation axis, a constant pressure that can always maintain a constant contact pressure regardless of the amount of wear on the grinding wheel 4 is created. A polishing mechanism can be formed. Hereinafter, the detection mechanism D for detecting the elastic displacement of the grindstone rotating shaft 2 will be explained. Reference numeral 14 denotes a holder for an elastic displacement detector, which is fixed to the constant pressure polishing head 1 in a suitable manner. Inside the detector holder 14, there are three displacement detectors that detect the elastic displacement of the grindstone rotating shaft 2 along the X-axis, Y-axis, and Z-axis directions;
For example, a differential transformer is fixed. The first detector 15 is a detection means for detecting elastic displacement of the grindstone rotation shaft 2 in the X-axis direction, and is a detection means for detecting elastic displacement of the grindstone rotation shaft 2 in the X-axis direction.
The elastic displacement in the XY plane is measured by the first
The displacement is converted into a displacement in the Z-axis direction via a measuring element 19 and a displacement conversion lever 17 for detection. The displacement conversion lever 17 is swingably supported around a pin 18 as a center of rotation, and uses the swinging motion to convert a radial displacement of the grindstone rotating shaft 2 into a displacement in the Z-axis direction. A measuring element designated by reference number 16 is a second measuring element fixed to the tip of the first detector 15. The elastic displacement of the grindstone rotating shaft 2 along the Y-axis direction is also detected by a second detector (not shown) having the same structure as the first detector 15 described above. However, the second detector is arranged such that its angular position is offset by approximately 90 degrees with respect to the first detector 15. Reference number 2
The third detector indicated by 1 is the Z of the grinding wheel rotation axis 2.
It is provided for the purpose of detecting elastic displacement along the axial direction, and when the third probe 22 fixed to the detector is brought into contact with the holder 7, the Z of the holder is
It is configured to be able to detect axial displacement, that is, elastic displacement of the grindstone 4 along the Z-axis direction.

On the other hand, the constant-pressure polishing head 1 has three displacement detectors for detecting the elastic displacement of the grinding wheel rotating shaft 2 along the X-axis, Y-axis, and Z-axis, and sends electric signals to the computer. A signal extraction device is attached for this purpose. More specifically, FIG. 1 shows the constant pressure polishing head 1 connected to the main shaft 26 of a machining center, and reference numeral 23 indicates an arm protruding from the constant pressure polishing head 1. Reference number 24 is
A signal sending rod is shown extending in a direction substantially perpendicular to the axis of the arm 23. displacement detector 15,
The electrical signal transmitted from 21 etc. is transmitted to arm 23,
Electrical connector 2 attached to signal sending rod 24
5. On the other hand, a spindle cap 27 fixed to the front surface of a spindle head (not shown) is disposed around the spindle 26, and a signal take-out block 28 and an electrical connector 2 are attached to the spindle cap.
9 is installed in a positioned state. Therefore, at the same time that the constant-pressure polishing head 1 is mounted on the spindle 26 from the tool magazine by a known automatic tool changer, the electric signal cables extending from the three displacement detectors are connected to the computer connected to the machining center (Fig. (not shown) will be automatically connected to the connection terminal. The compressed air supply route to the air motor-driven grinding wheel rotating shaft 2 is also
Similar to the electrical signal system described above, the constant pressure polishing head 1 is put into communication with the main shaft 26 at the same time.

Hereinafter, a method for polishing the surface of a workpiece using the apparatus of the present invention will be explained based on FIG. In the following description, in order to facilitate understanding, the case where a circular grindstone is used will be explained. For simplification, Figure 2 shows the constant pressure polishing head 1 shown in Figure 1.
This diagram schematically shows a case where elastic displacement occurs only within the XZ plane. The constant pressure polishing head 1 is elastically supported by two coil springs with spring constants K _x and K _z .
Spring constant K _x in the X-axis direction and spring constant K _z in the Z-axis direction,
Further, the spring constants K _y in the Y-axis direction are adjusted to be equal to each other. Reference number S _u in FIG. 2 indicates the surface of the workpiece W that has been roughly finished by a cutting tool such as a ball end mill in the previous process. A locus L _p that is offset by an amount equal to the radius r of the grindstone 4 in the normal direction to the surface S _u
Even if the grindstone 4 moves while rotating on the top,
Since the contact pressure acting between the grindstone and the workpiece is almost zero, substantially no polishing is performed. Therefore, in this state, the output signals of the displacement detectors 15 and 21 become almost zero.

Here, in order to apply the contact pressure necessary for polishing between the grinding wheel 4 and the workpiece W, a combined displacement E = √ _x ² + _z ² is applied to the roughly finished surface S _u of the workpiece ( However, E _x is the elastic displacement along the X-axis direction of the grinding wheel rotation axis 2, and E _z is the elastic displacement along the Z-axis direction of the grinding wheel rotation axis 2), and the envelope of the surface of the grinding wheel 4 is S _p The grindstone 4 is moved so that In this way, the surface of the workpiece is polished while maintaining the contact pressure corresponding to the resultant displacement E.

The following three technical issues should be considered at this time:
Items are listed.

The amount of pushing required to apply a constant contact pressure, that is, the setting accuracy of the resultant displacement E, the measurement accuracy of the grindstone radius r, and the increase in the amount of grindstone wear over time.

All of the above three items are factors that cannot be ignored when setting the contact pressure, but since it is difficult to understand them quantitatively, conventional polishing processes rely on the operator's experience and rely on trial and error. Therefore, it was necessary to correct the contact pressure each time. That is, since the grinding wheel 4 itself is an elastic body, the measurement accuracy of the diameter 2r of the grinding wheel 4 is not necessarily high, and the change in the diameter and shape of the grinding wheel due to wear is not uniform, making it impossible to quantitatively understand it. Due to certain factors, conventional polishing processes have experienced significant difficulties in maintaining contact pressure at a constant level.

By adopting the method of the present invention, the above problems are solved all at once, and a constant contact pressure is always maintained between the grinding wheel 4 and the work surface S _u without being affected by the elastic displacement or amount of wear of the grinding wheel. You can force it.

Hereinafter, a rectangular coordinate diagram in which the movement trajectory S _p of the envelope of the grinding wheel surface in FIG. 2 is subdivided into minute sections Δx along the X-axis direction is shown as FIG. 3, and
At that time, the resultant displacement E of the grindstone rotating shaft 2 and the contact pressure P
(=k·E) The features of the present invention will be described in detail with reference to FIG. 4, which is a graph schematically showing the relationship between In conventional surface polishing methods, the movement trajectory of the grinding wheel 4 is defined by the machining program for the workpiece W that is input into the computer in advance, so the grinding wheel 4 is 4 is designated by the reference number S _p in FIG. Assuming that the wear amount of the grindstone 4 gradually increases as it moves from position X ₄ to X ₇ , the actual movement locus of the grindstone surface changes as shown in S ₁ . As a result, the combined displacement E and the contact pressure P change as shown in a and b in FIG. 4 in response to the amount of wear, and normal polishing is not performed.

On the other hand _, in the method of _{the present invention, as shown in FIG .} The displacement detection signal is detected as a displacement detection signal, and by distributing the displacement detection signal into each axis component by a distributor (not shown) and comparing it with the command register of each axis, the workpiece that has been input into the computer in advance can be detected. The command value of the machining program is corrected. That is, in the present invention, as shown in FIG. 3, the surface of the grindstone 4 draws a movement trajectory S ₂ that is obtained by adding or subtracting corrections ΔE ₁ to ΔE ₄ to the trajectory movement S ₁ , and as a result, The contact pressure P will be maintained at a constant level, as indicated by reference numeral b' in FIG.

FIG. 5 is a flowchart illustrating the signal flow of the correction operation in FIG. This is the sending route of the command, and the signal flow indicated by the bold line arrow is the sending route of the movement command of the grindstone rotating shaft 2 corrected by the method of the present invention.

C. Effects of the Invention As can be understood from the above explanation, by inputting the detection signal of the elastic displacement of the grinding wheel rotating shaft transmitted from the constant pressure polishing head to the computer connected to the numerically controlled machine tool, the distance between the grinding wheel and the workpiece can be Surface polishing conditions are obtained in which the contact pressure is always maintained at a constant level. According to the present invention, the machining program of the workpiece, especially the movement trajectory of the grinding wheel rotation axis, is automatically corrected in response to wear and changes in the shape of the grinding wheel, so that the polishing process can be performed under the action of a stable and constant contact pressure. is carried out. Therefore, the dimensional accuracy of the workpiece surface is significantly improved compared to conventional polishing methods. Furthermore, by monitoring the detection signal of the elastic displacement, it is possible to detect the contact pressure acting between the grindstone and the workpiece, and to quantitatively manage the amount of wear of the grindstone. Further, by using an external work offset mechanism and a tool radius offset mechanism of a known numerical control device, numerically controlled profile polishing can be performed simply by attaching a constant pressure polishing head to a general-purpose numerically controlled machine tool.

[Brief explanation of the drawing]

FIG. 1 is a partial longitudinal cross-sectional view illustrating the main structure of a surface polishing apparatus according to the present invention, and FIG. 2 is a schematic explanatory diagram of the method of the present invention. Also, Figure 3 shows
This is an orthogonal coordinate diagram that subdivides and displays the movement locus of the envelope of the grinding wheel surface in Fig. 2 above in minute sections Δx along the X-axis direction, and Fig. 4 shows the resultant displacement of the grinding wheel rotation axis. It is a graph schematically displaying the relationship with contact pressure. Furthermore, FIG. 5 is a flowchart illustrating the signal flow of the correction operation in FIG. 4. DESCRIPTION OF SYMBOLS 1... Polishing tool, 2... Grindstone rotating shaft, 3... Floating support mechanism for grinding wheel rotating shaft, D... Elastic displacement detection mechanism, 26... Main shaft of numerically controlled machine tool.

Claims (1)

[Scope of Claims] 1. In polishing the surface of a workpiece using a tool of a constant-pressure polishing head mounted on the main shaft of a numerically controlled machine tool, a grindstone rotating shaft is supported elastically with respect to the constant-pressure polishing head, and the workpiece is polished. The elastic displacement of the grinding wheel rotation axis in the X-axis, Y-axis, and Z-axis directions due to contact with the grinding wheel is detected as the amount of displacement in the axial direction of the grinding wheel rotation axis, and the detected displacement amount is input into the workpiece machining program that has been input into the computer in advance. A surface polishing method characterized in that a workpiece surface is polished at a constant pressure by moving a grindstone while correcting the locus of movement of a grindstone rotation axis by adding or subtracting from a command value. 2. A floating support mechanism that supports the grinding wheel rotation shaft of a constant pressure polishing head mounted on the main shaft of a numerically controlled machine tool so as to be elastically displaceable with respect to the constant pressure polishing head; a detection mechanism that detects each elastic displacement in the axial direction as an electrical signal representing the amount of displacement in the axial direction of the grinding wheel rotating shaft; and a workpiece machining device connected to the numerically controlled machine tool and into which the amount of displacement according to the detection signal is input in advance. A surface polishing apparatus characterized in that a constant pressure polishing mechanism is formed by a computer that corrects a command value of a program by adding or subtracting it.