JPH0448578B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method and apparatus for surface polishing, and more particularly to a method and apparatus for constant-pressure polishing of the surface of a workpiece in a machine tool having a profile control device such as a copy milling machine. It is something.

Conventional technology When machining a workpiece with a free-form surface, for example, when manufacturing a mold, the rough finishing is usually first performed using a machine tool equipped with a copy control device such as a copy milling machine, and then smoothed using a manual polishing tool such as a hand grinder. Perform processing, so-called surface polishing.
Since highly automated machine tools are used for rough finishing, highly efficient automatic machining is possible. On the other hand, the reality is that surface polishing relies on manual finishing by workers, which poses major constraints in automating the surface polishing process and improving work efficiency and product dimensional accuracy. It was recognized. Naturally, various measures have been proposed in response to the demand for automation of such surface polishing process.
As an example, a method is known in which a polishing wheel shaft is attached to the main shaft of a copying machine tool, and the rotation of the main shaft is used to polish the surface of a workpiece, such as a mold. Hereinafter, a known example of surface polishing using a copy milling machine will be explained based on FIG. FIG. 4 schematically shows rough machining, ie, cutting, of the surface of the workpiece 3 by a known copy milling machine. Work 3 and work 3 are on table 1.
A model 2 having a curved surface shape corresponding to the rough finished surface to be formed is fixed to the model 2, and a cantilever-shaped tracer arm with a tracer head 6 attached to the tip is attached to the spindle head 4 of the copy milling machine. 5 is fixed. During copy cutting, the feeler 7 attached to the tip of the tracer head 6 is moved while being in contact with the surface of the model 2,
Execute copying motion. The displacement detection signal Ex transmitted from the tracer head 6 by this tracing operation,
Ey and Ez are processed by a known copy control device 8 attached to the copy milling machine, and sent as a movement command to the servo motor 9 that drives the spindle head 4 and table 1 of the copy milling machine. The rotational driving force of the servo motor 9 based on the movement command is:
Spindle head 4 and table 1 via feed screw 10
This causes the feeler 7 to move along the surface of the model 2. The spindle head 4 includes a spindle 11 equipped with a cutting tool 12 such as a ball end mill.
Since the cutting tool 12 is rotatably supported, the cutting tool 12
The same copying motion as that of the spindle head 4 is transmitted to
The workpiece 3 is cut into the same surface shape as the model 2 by the above-described copying operation.

The standard copy cutting process using a ball end mill has been described above, but when surface polishing is performed using the copy milling machine shown in FIG. 4, the method described below is adopted. That is, a polishing wheel is attached to the main spindle 11 instead of the cutting tool 12, and a tracing operation is performed on the surface of the model 2 according to the same procedure as the copying cutting process described above, and the surface of the workpiece is polished with the polishing wheel. .

Problems to be Solved by the Invention In the process of polishing the surface of a workpiece using the copy milling machine, the center movement locus of the polishing wheel is uniquely determined by the copying motion between the model 2 and the filler 7. The reality is that it is not possible to obtain a free-form surface with dimensional accuracy that satisfies practical requirements only through motion. The following factors are considered to be the reason for this.

A grinding wheel generally has lower rigidity than a cutting tool, and the degree of wear of a grinding wheel is an order of magnitude greater than that of a cutting tool. For this reason, even if the polishing wheel is given the same movement trajectory as the cutting tool,
There are cases where the grinding wheel becomes idle due to changes in the shape of the grindstone due to wear.

Chips are discharged only by displacing the grinding wheel relative to the workpiece while applying contact pressure. In order to maintain this function, it is necessary to adjust the relative position between the grinding wheel and the workpiece so that a constant contact pressure is always applied. However, since the grinding wheel itself has considerable elasticity, and the shape and dimensions of the grinding wheel change irregularly as the grinding wheel wears, it is practically impossible to maintain a constant contact pressure. It is extremely difficult.

A method of incorporating a mechanism that maintains a constant amount of displacement of the feeler 7, that is, the amount of pushing when the feeler 7 contacts the model 2 into the copying control device, and gradually increasing the amount of displacement of the feeler 7 according to the amount of wear of the grinding wheel. However, this method requires the operator to manually adjust the amount of displacement of the feeler 7 each time, and since the amount of displacement to be adjusted is itself warm, it is necessary to maintain the contact pressure at a constant level. This naturally hinders the automation of the polishing process and the improvement of workpiece machining accuracy.

A main object of the present invention is to provide a novel surface polishing method and apparatus that can overcome the above-mentioned disadvantages observed in workpiece surface polishing means using conventional copying machine tools.

Means for Solving the Problems The method of the present invention supports a grinding wheel rotating shaft having a grinding wheel at its tip so as to be elastically displaceable in the X-axis, Y-axis, and Z-axis directions with respect to the polishing tool body. The grindstone attached to the main spindle of a machine tool presses the tip of the grindstone against the surface of the workpiece with a constant pressure, and in this state, the main spindle of the machine tool is moved along the X-axis and Y-axis of the grindstone rotation axis due to the contact between the grindstone and the workpiece. and the amount of elastic displacement in the Z-axis direction, and controls the tracing motion of the main shaft of the machine tool so that the composite value of the detected displacement amounts becomes a constant value, thereby polishing the surface of the workpiece under constant pressure. .

The device of the present invention also includes a polishing tool body that supports a grindstone rotating shaft having a grindstone at its tip so as to be elastically displaceable in the X-axis, Y-axis, and Z-axis directions via a floating support mechanism, and the polishing tool body. The main shaft of a machine tool that is installed and presses the grindstone at the tip against the surface of the workpiece under a constant pressure and performs a copying operation while polishing the surface of the workpiece under a constant pressure, and each elastic displacement of the grindstone rotation axis in the X-axis, Y-axis, and axial direction. A detection mechanism converts the amount of displacement in the axial direction of the grinding wheel rotation axis and detects it as an electrical signal, and the detection signal obtained by this detection mechanism is synthesized, and the said machining is performed so that this synthesized value becomes a constant value. It is equipped with a copying control device that controls the copying of the main shaft of the machine.

Effects According to the method of the present invention, the polishing tool body is moved to follow the surface of the workpiece via the main axis of the machine tool, and at that time, displacements of the polishing tool in the X-axis, Y-axis, and Z-axis directions are detected, The workpiece surface is polished at a constant pressure by controlling the tracing motion of the main spindle of the machine tool so that the resulting amount of displacement remains constant.In short, changes in the shape of the workpiece are directly detected at the point where the grinding wheel is in contact with the workpiece. Since the surface of the workpiece is being polished while being detected, the contact pressure can be automatically kept constant and surface polishing can be carried out efficiently.

Furthermore, in the case of the device invention, the surface of the workpiece can be polished with the same effect as the method invention described above.

Embodiment FIG. 1 is a front view showing the overall structure of a copy milling machine illustrating the apparatus of the present invention, and FIG. 2 is a partial vertical sectional view schematically showing the structure of a constant pressure polishing head. In these drawings, reference numeral 21 indicates the main body of the polishing tool, which can be mounted on the main shaft of any machine tool by moving a tool shank (not shown) in accordance with the shape of the main shaft of the machine tool. Reference number 22 indicates the rotation of the grindstone, and in this embodiment, an air motor type (vane type) is used. That is, by introducing high-pressure compressed air from the air inlet 23 provided at the base end of the whetstone rotating shaft 22, the whetstone 24 is heated.
High speed rotation of 10000RPM or more is provided. A flange 25 extending in a direction perpendicular to the axis of the whetstone rotation shaft is provided on the body of the whetstone rotation shaft 22, and a conical pressure receiving surface 26 is formed on the surface of the flange 25 on the whetstone 24 side. ing. These flanges 25 and pressure receiving surfaces 26 are connected to steel balls 28a, 28
It is floatingly supported on the holder 27 via b and 29 so as to be elastically displaceable. More specifically, the flange 25 is rotatably supported by a plurality of steel balls 28a and 28b arranged oppositely on the same circumference. 21 so that it can be freely displaced within the XY plane.
Moreover, on the conical pressure receiving surface 26, a plurality of steel balls 2
9 are arranged on the same circumference at approximately equal intervals, and these steel balls 29 constantly receive pressure in the negative direction of the Z-axis due to the compression reaction force of the coil spring 31 fitted in the retainer 30. The surface 26 is pressed. By employing such a floating support structure S, the grindstone rotating shaft 22 is automatically positioned at a dynamically stable zero point.

When a reaction force is generated on the grindstone 24 due to contact with the workpiece 3 during polishing of the workpiece 3, the grindstone rotating shaft 22 tends to be displaced relative to the holder 27 in the XY plane, but due to this relative displacement, Natsute Steel Ball 2
9 and the coil spring 31 are compressed and moved in the positive direction of the Z axis. Therefore, movement resistance corresponding to the inclination angle of the conical pressure receiving surface 26 and the compression reaction force of the coil spring 31 is generated on the grindstone rotating shaft 22 .

Further, the holder 27 is supported so as to be linearly movable in the Z-axis direction via a linear guide element 32 such as a ball slide, and is constantly pressed in the positive direction of the Z-axis by a coil spring 33. Therefore, the grindstone 24
If a contact reaction force occurs in the negative direction of the Z-axis, the entire grinding wheel rotation shaft 22 is moved toward the linear guide element 3.
2 and retreat in the negative direction of the Z axis.
Since the surface polishing apparatus according to the present invention, particularly its constant pressure polishing head, is constructed as described above, the grindstone rotating shaft 22 has a self-restoring property that automatically returns to a dynamically stable zero position at all times. , and displacement in any direction is allowed depending on the direction and magnitude of the polishing resistance acting on the grindstone 24. Furthermore, coil spring 3
1 and 31, a reaction force proportional to the amount of deflection of the grinding wheel rotation shaft 22 is generated, so a proportional relative relationship is established between the load applied to the grinding wheel 24 and the displacement of the grinding wheel rotation shaft 22. ing.

As can be understood from the above explanation, the grinding wheel rotation shaft 2
Since the load applied to the grinding wheel 2 appears as an elastic displacement of the grindstone rotating shaft 22, the elastic displacement detection mechanism D will be explained here. Reference number 34 is the grindstone rotating shaft 2
Three displacement detectors 35, 3 detecting the displacement of
7, 41 fixed inside, the detector holder is a polishing tool main body 21.
It is fixed to via suitable fixing means. A first detector 35 that detects the displacement of the whetstone rotation shaft 22 in the X-axis direction is configured to detect the displacement of the whetstone rotation shaft 22 in the XY plane.
Forms a detection mechanism that converts the displacement in the X-axis direction into a displacement in the Z-axis direction via the measuring element 39 that contacts the reference ring 40 formed on the body of the grindstone rotating shaft 22 and the displacement conversion lever 37. are doing. The displacement conversion lever 37 is swingably supported around a pin 38 as a center of rotation, and through its swinging movement, the displacement in the X-axis direction, that is, the radial displacement, of the grindstone rotating shaft 22 is converted into the displacement in the Z-axis direction, In other words, it is converted into displacement in the axial direction. A displacement in the Y-axis direction of the grindstone rotating shaft 22 in the XY plane is also detected by a second detector (not shown) having the same structure as described above.
However, the fixed position of the second detector is adjusted so that the position of the measuring point is shifted by 90 degrees with respect to the position of the measuring point 39 of the first detector 35. . Reference number 41 is a third detector for detecting the displacement of the grinding wheel rotating shaft 22 along the Z-axis direction. In other words, it is configured to be able to detect the displacement of the grindstone 24 along the Z-axis direction. The main body 21 of the polishing tool also has an inlet 23 for introducing high-pressure compressed air supplied from an external compressed air source through a connection port 43.
An electrical connector 44 is provided for sending electrical displacement detection signals Ex, Ey, and Ez from the three displacement detectors to a tracing control device (not shown) of the machine tool.

FIG. 3 is a schematic diagram illustrating a method of performing copy polishing by attaching the constant pressure polishing head illustrated in FIG. 2 to the main shaft 11 of a copy milling machine. In the following description, a case will be described in which a circular grindstone 24 is used as the polishing tool to facilitate understanding. In FIG. 3, the reference number Su indicates the surface of the workpiece 3 that has been roughly finished by a cutting tool such as a ball end mill. Assuming that the whetstone 24 moves on a locus Lo with an offset r equal to the radius of the whetstone 24 in the normal direction to the surface Su, the whetstone 24 has the rotational drive necessary for polishing. Even if force is transmitted, the contact pressure acting between the grindstone 24 and the workpiece 3 is almost zero, so normal polishing is not performed. Furthermore, in this state, the output of the detection signals from the three displacement detectors incorporated in the polishing head illustrated in FIG. 2 is naturally zero, so that the copying operation itself becomes impossible. In the present invention, similarly to known copying control, the grinding wheel 2 is adjusted so that the resultant displacement E is maintained at a constant value.
4 into the workpiece 3, and at the same time, the locus of movement of the grindstone 24 is controlled so that the level of the composite displacement E does not substantially change. Generally, the resultant displacement E
is expressed as E=√ ² + ² + ² , but
For ease of understanding, in the embodiment shown in Fig. 3, it is assumed that displacement occurs only in the XZ plane, and the constant pressure polishing head shown in Fig. 2 has a spring constant.
Assume that it is elastically suspended and supported by two coil springs having kx and kz. Whetstone 2
4 with respect to workpiece 3 E = √ ² + ²
When pushed in by a length corresponding to , a coil spring with spring constants kx and kz is compressed depending on the magnitude and direction of the contact reaction force. The kx and kz are spring constants of the coil spring in the X-axis and Z-axis directions, respectively, and are usually adjusted so that kx=kz.

The displacement Ex and Z of the coil spring in the X-axis direction
The axial displacement Ez is detected as an electrical signal by the displacement detectors 35 and 41, and sent to the copying control device 8 of the copying milling machine. Copying control device 8
has a built-in arithmetic mechanism that converts the detection signal into a movement command for the grinding wheel rotating shaft 22, and is designed to maintain the composite displacement of the displacement detection signals Ex and Ez at a constant level at all times as shown in FIG. A rotation command is sent to the X-axis servo motor and Z-axis servo motor indicated by reference number 9. X-axis servo motor and Z
Due to the rotation of the shaft servo motor, a copying motion corresponding to the displacement detection signals Ex and Ez is transmitted to the grindstone rotating shaft 22, and the envelope of the surface of the grindstone 24 is
In Fig. 3, we draw a curved surface called So, which is indicated by a chain double-dashed line. By moving the grindstone 24 along the curved surface So under rotational drive, the grindstone contacts the surface Su of the workpiece 3 with a constant contact pressure, and polishes the surface of the workpiece 3 under constant pressure while performing a copying operation. .

In the method of the present invention, even if the grinding wheel 24 wears out as the workpiece machining progresses, the displacement of the grinding wheel rotating shaft is always controlled to be constant. Regardless, the contact pressure between the workpiece 3 and the grindstone 24 does not substantially change.
Therefore, the workpiece 3 can obtain good surface accuracy based on constant pressure polishing.

Effects of the Invention According to the method of the present invention, a change in the shape of a workpiece is directly detected with a grindstone and the surface of the workpiece is polished by controlling the tracing, so that a constant contact pressure is always maintained on the surface of the workpiece. The grindstone can be pressed against the grinding wheel, and the surface can be polished efficiently.

Further, according to the device of the present invention, the grindstone rotating shaft is floatingly supported within the polishing tool body so as to be elastically displaceable in the X-axis, Y-axis, and Z-axis directions, and a detection mechanism for displacement in each of these directions is provided. The structure is very simple because it is attached to the main shaft of a machine tool and controls the main shaft of the machine tool so that the composite value of the detected values from the above detection mechanism is constant. It is simple and allows the surface polishing of a workpiece to be performed automatically, efficiently, and with high accuracy by using a conventional copying machine tool as is.

[Brief explanation of the drawing]

FIG. 1 is a front view showing the overall structure of a copy milling machine illustrating the apparatus of the present invention, and FIG. 2 is a partial vertical sectional view schematically showing the structure of a constant pressure polishing head. Moreover, FIG. 3 is a schematic explanatory diagram of the method of the present invention. FIG. 4 is an explanatory diagram illustrating a known surface polishing process using a copy milling machine. 22... Grinding wheel rotating shaft, 24... Grinding wheel, 8... Copying control device, 3... Workpiece, S... Floating support mechanism, D... Elastic displacement detection mechanism.

Claims (1)

[Claims] 1. A grindstone rotating shaft having a grindstone at its tip is supported so as to be elastically displaceable in the X-axis, Y-axis, and Z-axis directions relative to the polishing tool body, and the polishing tool body is mounted on the main shaft of the machine tool. The grindstone at the tip is pressed against the surface of the workpiece with a constant pressure, and in this state, the main shaft of the machine tool is moved to follow, and the elasticity of the grindstone rotation axis in the X-axis, Y-axis, and Z-axis directions due to the contact between the grindstone and the workpiece is measured. A surface polishing method comprising: detecting the amount of displacement, and controlling the tracing operation of the main shaft of the machine tool so that a composite value of the detected displacement amounts becomes a constant value, thereby polishing the surface of the workpiece at a constant pressure. 2. A polishing tool body that supports a whetstone rotating shaft having a whetstone at the tip so that it can be elastically displaced in the X-axis, Y-axis, and Z-axis directions via a floating support mechanism, and this polishing tool body is attached, and the whetstone at the tip is attached. The main shaft of a machine tool that presses against the work surface with a constant pressure and performs a copying operation while polishing the work surface under a constant pressure, and the X of the grindstone rotation axis.
A detection mechanism that converts each elastic displacement in the axis, Y-axis, and Z-axis directions into an amount of displacement in the axial direction of the grindstone rotation axis and detects it as an electrical signal, and a detection signal obtained by this detection mechanism is synthesized, A surface polishing apparatus comprising: a tracing control device that controls the main axis of the machine tool to trace so that the composite value becomes a constant value.