JPS618202A - Machine tool for article having noncircular section - Google Patents

Abstract

PURPOSE:To permit the working with high accuracy by relatively shifting a tool rest in the direction of Y-axis by a prescribed distance corresponding to the position in the direction of X axis and shifting a tool by the difference between the radius of the sectional surface form at each revolution angle position and the position of the tool rest in the direction of Y-axis. CONSTITUTION:A workpiece W is set onto the main spindle 3 of a lathe 1 and revolved around the revolution axis line O. When a tool 13 is set at a position IIon the standard plane of an aimed article, and the workpiece W is revolved, a hydraulic cylinder 15 is operated by the signal corresponding to the revolution angle theta of a computer 8, and the position of the tool 13 in the direction of Y-axis, is controlled, and the tool 13 is shifted in the direction of Y-axis according to the angle theta, and the workpiece W is lathed into noncircular sectional form. At the samt time, a feed screw 5 is turned to shift a tool rest 9 in the direction of X-axis, and the tool 13 is shift-controlled in the Y-direction with respect to the tool rest 9 by the output signal corresponding to the position X of the computer 8 and the revolution angle theta.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a machine tool suitable for machining a workpiece into a non-circular cross section, and in particular, it relates to a machine tool suitable for machining a workpiece into a non-circular cross section. The invention relates to a machine tool such as a lathe or a grinder for machining into a non-circular cross section.

(Prior Art) Articles that require machining are not limited to those with a circular cross section, but there are also many items that require machining to have a non-circular cross section, such as camshafts and rotary engine rotors. , shaft joints, etc., can be made highly reliable if the shaft itself is processed to have a non-circular cross section.

To process objects with such non-circular cross sections, it is conceivable to use a milling machine or the like that moves the tool in the axial direction of the workpiece, but the target cross-sectional profile of the workpiece is a smooth closed curve. In such cases, machining using a milling machine or the like is not only inefficient, but also has low machining accuracy.Therefore, in the past, in such cases,
It was common to use a hydraulic copying lathe, etc., which controlled the position of the cutting tool relative to the rotated workpiece using a copying model. However, with such a hydraulic copying lathe, it is necessary to produce a copying model for each desired shape of an article, and it cannot be said to be suitable for a wide variety of products.

In order to deal with such problems, it is conceivable to use an NC machine tool that can control the position of a tool with respect to a rotated workpiece by numerical control (hereinafter referred to as NG). In theory, with an NC machine tool, a workpiece can be machined into any shape by simply changing the program or data. Therefore, if the position of the tool is controlled according to the rotation angle of the spindle, even articles with non-circular cross sections can be processed.

By the way, in a normal NC machine tool, the tool is fixed on a tool rest, and the tool rest is rotated in a direction parallel to the main axis, that is, the rotational axis of the workpiece (hereinafter referred to as the X-axis direction).
and the vertical direction (hereinafter referred to as the Y-axis direction). And as for its movement mechanism.

A feeding mechanism in the X-axis direction and the Y-axis direction using a servo motor and a pole screw is used. When such a feeding mechanism is used, highly accurate position control can be performed over a long distance from several hundred mm to several thousand layers. However, on the other hand, such a feeding mechanism using a ball screw has a problem in that the feeding speed is slow. For this reason, if you try to machine an article with a non-circular cross section by controlling the position of the tool in the Y-axis direction using a conventional NC machine tool, the tool will not work properly unless the rotation speed of the spindle is reduced to less than a few revolutions per minute. It was not possible to make the position respond to the rotation angle of the workpiece. On the other hand, in order to ensure a good finished surface and machining efficiency, it is required that the rotation speed of the main shaft be 100 rotations or more. For this reason, conventional NC
In practice, it has been difficult to process articles with non-circular cross sections using machine tools.

In view of these circumstances, the present inventor proposed an NC machine tool in which the positioning of the tool in the Y-axis direction is performed by an electro-hydraulic servo mechanism (Japanese Patent Application No. 58-53130).
No. 5), such electro-hydraulic servomechanisms are excellent in terms of high-speed response and power, so NC machine tools using them can efficiently process objects with non-circular cross sections. It becomes like this. By the way, when positioning the tool is performed by an electro-hydraulic servo mechanism like this,
Most commonly, the tool is driven by a hydraulic cylinder. However, when using a hydraulic cylinder, there is a problem in that the stroke of the tool is limited to the effective operating range of the hydraulic cylinder.

It is possible to increase the stroke by using a longer hydraulic cylinder, but this increases the weight of the moving parts and increases the inertia, and also causes problems such as the compressibility of the hydraulic fluid in the cylinder. Furthermore, in hydraulic cylinders, there is also the problem that the dynamic characteristics vary depending on the position of the piston within the cylinder.For example, when the piston is near the end of the cylinder, A difference occurs between the characteristics when the piston moves toward the end of the cylinder and the characteristics when it moves toward the center. Therefore, when positioning a tool using a hydraulic cylinder, it is difficult to perform highly accurate machining unless the center of the reciprocating motion of the piston is always located near the center of the cylinder.

As described above, even with NC machine tools using electro-hydraulic servomechanisms, problems still remain when attempting to process with high precision an article that has a large difference between the minimum radius and maximum radius of the target machining shape.

(Objective of the Invention) The present invention has been made in view of such problems, and its purpose is to minimize the reciprocating stroke of the tool itself, which needs to be reciprocated at high speed in NC machine tools. The purpose of the present invention is to enable the position of the tool relative to the workpiece to be changed significantly while the tool remains the same, thereby enabling high-speed response and high-precision machining.

(Means for Achieving the Object) In order to achieve this object, in the present invention, a tool is mounted on a tool stand that is installed to be movable relative to the workpiece in the X-axis direction and the Y-axis direction. The tool stand is supported so as to be able to reciprocate in the direction, and the positions of the tool stand and tools are controlled separately. The tool rest is relatively moved in the Y-axis direction by a predetermined amount corresponding to the position in the X-axis direction, based on the target machining shape of the workpiece. Further, the tool is moved according to the rotation angle of the workpiece by the difference between the radius at each rotational angular position of the target cross-sectional shape of the workpiece and the position of the tool rest in the Y-axis direction.

Therefore, since the position of the tool rest only needs to be controlled at a relatively low speed, the control device of a normal NC machine tool can be used as is. Although the position of the tool needs to be controlled at high speed, the present invention only needs to control the position relative to the tool stand, so a small stroke electro-hydraulic servomechanism can be used.

Next, the present invention will be explained in more detail based on the drawings.

Now, as shown in Fig. 3, an article having a non-circular cross section and whose cross-sectional shape changes in the axial direction is subjected to NC processing.
Consider the case of turning with a lathe As shown in Figure 0, the distance from the center axis of the object is r, the angle from the reference plane I that includes the center axis is θ, and the reference plane ■ perpendicular to the center axis When the distance between is set to X, the target processed contour shape of the article can generally be expressed as r=f (θ, x).

In this way, when turning a target article that can be expressed as r=f (θ+' Matches the rotation angle. Further, the direction of X coincides with the X axis. Therefore, the workpiece is defined as r=f(θ,
In order to turn the workpiece into the contour shape represented by 1, where Y.

is a constant representing the distance between the reference point for feeding in the Y-axis direction of the lathe and the rotation axis 0 of the workpiece.

If it is assumed that the cutting edge of the tool is located on the rotational axis O when Y-0, then yo=o. Even if this is done, generality is not lost, so in the following explanation, it is assumed that Y=0. Also, the position X of the cutting edge of the tool in the X-axis direction is.

X=X+X.

Control so that Here, XO is the distance between the reference point for feeding in the X-axis direction of the lathe and the reference plane (■) of the target article. Since the generality is not lost even if the cutting edge of the tool is on the reference plane (2) when x=0, in the following explanation, it is assumed that X0=O.

In this way, when controlling the position of the tool separately in the X-axis direction and the Y-axis direction, it is sufficient that X=x is satisfied in the X-axis direction. That is, any control may be used, such as moving at a constant speed in the X-axis direction or changing the moving speed depending on the magnitude of cutting resistance.

Such control can be performed with sufficient accuracy using a feed mechanism using a pole screw in a normal NC lathe.

In the Y-axis direction, Y=f(θ,X), that is, Y=f(θ
, x). Therefore, it is necessary to perform high-speed control in synchronization with the rotation angle θ of the workpiece. By the way, the function f (θ, x) representing the contour shape of such an article has a part fl (θ, x) that changes depending on the rotation angle θ, a part fo (X) that does not need to be changed depending on the rotation angle θ, and a part fo (X) that does not need to be changed depending on the rotation angle θ. can be separated into That is, Y=f(θ,X)=fo(X)+ft(θ,X). Then, if fo(X) is selected appropriately, fx
The amplitude of (θ, X) can be made small. Furthermore, fo(X) generally changes slowly.

Therefore, in the present invention, the position of the tool stand in the Y-axis direction is fo
(X), and the tool supported on the tool stand so that it can reciprocate in the Y-axis direction is controlled by f+ (θ, x).

An example of a specific configuration for this purpose is shown in FIGS. 1 and 2. In these figures, FIG. 1 is a plan view showing an example of the NC lathe according to the present invention, and FIG. 2 is a front view thereof. .

As is clear from these figures, the base 2 of this lathe 1
A linear motion guide surface 2a in the X-axis direction parallel to the rotation axis O of the main shaft 3 is provided on the top, and on this guide surface 2a,
A movable table 4 is slidably supported. The position of the movable table 4 in the X-axis direction is controlled by a feed screw 5 rotatably supported by the base 2. A general servo motor can be used for this control.
For example, when a step motor is used, the feed screw 5 is rotated by a step motor 7 driven by an oscillator 6, and the oscillator 6 generates a signal based on a command signal from a computer 8. . Therefore, the position of the moving table 4 in the X-axis direction is
It is always understood by

A tool stand 9 is supported on the upper part of the movable table 4 so as to be slidable in the Y-axis direction perpendicular to the rotation axis 0 of the main shaft 3 of the lathe 1 . As shown in FIG. 2, a feed screw lO in the Y-axis direction is rotatably supported on the moving table 4.
A ball nut 9a provided on the tool stand 9 is engaged with the ball nut 9a. The feed screw 10 is rotated by a servo motor 11 that operates based on a command signal from the computer 8. The computer 8 generates a signal proportional to fo(X) according to the position of the moving table 4 in the X-axis direction, thereby causing the tool table 9 to move f in the Y-axis direction.
It is configured to be moved by o(X).

The tool stand 9-L is provided with a linear motion guide surface 12 in the Y-axis direction, and a tool holding member 14 that holds a tool 13 is supported so as to be able to reciprocate along this guide surface 12. The position of this tool holding member 14 in the Y-axis direction is controlled by a hydraulic cylinder 15 installed on the tool stand 9. This hydraulic cylinder 15 forms part of an electrohydraulic servo mechanism 16, and a servo valve 17 is switched and controlled by a command signal from the computer 8.
The hydraulic pressure from the hydraulic pressure source 18 is thereby controlled.

A rotary encoder 19 is attached to the main shaft 3 of the lathe l, and the rotary encoder 19 detects the rotation angle θ of the main shaft 3, and the detection signal is guided to the computer 8. The computer 8 calculates fl (θ, x
), and controls the electro-hydraulic servomechanism 16 to move the tool 13 to the tool stand 9 at fl (θ,
x) in the Y-axis direction. The computer 8 calculates the position X of the tool 13 in the X-axis direction and the main shaft 3.
It may be possible to output fo (X) and fs (#, It may also be something that calculates and outputs those values.

(Function) Next, the function of the NC lathe configured as described above will be explained.

A workpiece W is set on the main shaft 3 of a lathe 1, and the workpiece W is rotated together with the main shaft 3 about its rotation axis O. Then, move the tool 13 to the reference plane of the target article.
Position it at the position of x=0. In this state, turn!
11 is activated, as the workpiece W rotates, the computer 8 generates a signal corresponding to the rotation angle θ, the hydraulic cylinder 15 is activated, and the position of the tool 13 in the Y-axis direction is controlled. . In this way, by moving the tool 13 in the Y-axis direction according to the rotation angle θ of the workpiece W, the workpiece W is turned into a non-circular cross-sectional shape.

At the same time, the feed screw 5 is rotated to move the movable table 4 and therefore the tool table 9 in the X-axis direction, and the
The axial position X changes.

As a result, the computer 8 outputs a signal corresponding to the current position Move by fl (θ, x) in the axial direction. Therefore, the position of the tool 13 in the Y-axis direction is 1iY
is Y= f o (X) + ft (θ, X)
The workpiece W is turned into a predetermined shape.

For example, the tool stand 9 is controlled as shown in FIG. 4(a),
Assuming that the tool 13 is controlled as shown in FIG. 5(b), the workpiece W is machined into the shape shown in FIG. 4(c). In the same figure (b), the amplitude represents the stroke in which the tool 13 is reciprocated according to fl (θ, x) while the workpiece W makes one rotation. That is, the tool 13 is moved at high speed with a relatively small stroke, and by configuring the control device using the electro-hydraulic servomechanism 16, such high-speed control becomes possible. In addition, since the position of the tool rest 9 only needs to be changed gradually, its control is similar to the tool rest control device in a normal NC lathe, which consists of a pole screw mechanism of the feed screw lO and the ball nut 9a, and a servo motor II. It is possible to perform accurate control even when the amount of control is large.

(Example) Next, an example will be described in which an article having a specific shape is machined using the machine tool shown in FIG. 1.2.

As shown in Fig. 5, for an article having a substantially triangular cross section and tapered in the axial direction, using cylindrical coordinates, r = rl) + kx + a ain3θ (ro, to, a
is an arbitrary constant). Therefore, when trying to obtain an article with such a shape, the position Y of the cutting edge of the tool 13 in the Y-axis direction is determined as follows: Y= ro + kX + a 5in3
It is sufficient to perform control so that θ is satisfied. Therefore, this formula is
If it is separated into a part fo (X) not related to θ and a part fl (θ, x) related to θ, it becomes f(1(X)=ro+kX fl (θ, X)=a 5in3θ.

In this way, fo(X) becomes an amount that changes linearly with respect to the amount of movement in the X-axis direction, and its control does not require high-speed responsiveness.

Therefore, this control can be performed using the feed when turning a taper on a normal NC lathe. Therefore, a tool stand position control device consisting of a servo motor 11, a feed screw lO, and a pole nara) 9a is used to control the tool stand 9 so that it is moved by ro+kX in the Y axis direction as it moves in the X axis direction. do.

On the other hand, fs (θ,

Therefore, the control is carried out by an electro-hydraulic servo mechanism 16, and the tool 13 is rotated at a 5in3θ in synchronization with the rotation angle θ of the main shaft 3 detected by the encoder 19.
control so that it is moved only.

In this way, the position Y of the tool 13 in the Y-axis direction can be controlled regardless of the rotation angle θ of the main shaft 3.
Separate into (X) = r(1+kX and the part molecule 1 (θ, By controlling the hydraulic servo mechanism 16, the center position of the amplitude of the hydraulic cylinder 15 in the servo mechanism 16 becomes constant, so that cutting is performed under almost the same conditions regardless of the position X in the X-axis direction. In addition, the hydraulic cylinder 15 only needs to have a stroke of 2a, and can be a hydraulic cylinder with a short effective operating range and a small weight of movable parts.On the other hand, if the Y-axis of the tool 13 If the entire directional position control is to be performed by a single hydraulic cylinder, that hydraulic cylinder will require a stroke of 2a+kh (h is the length of the target article).

Formula for determining the position Y of the cutting edge of the tool 13 in the Y-axis direction: Y=f
(θ, x) is a part unrelated to θ as in the above example fo(X) and a part fl
), the cross-sectional shape of the target workpiece at each position Xi in the X-axis direction is considered. Its cross-sectional profile is a closed curve as shown in FIG. 6, represented by f(θ, Xi). Therefore, the average radius from the center axis of the cross-sectional contour, that is, the average value of the maximum and minimum values of Y in the Xi section is determined. Letting the average value be Ya (Xi), Y (θ, Xi ) = Ya (Xi ) + (f
(θ, Xi) −Ya (Xi)).

Therefore, if such an average value Ya(Xi) is obtained for each position in the X-axis direction, Y=Ya(X)+(f(θ,X)−Ya(X)) can be obtained. By doing this, Ya(X) becomes a term unrelated to θ, so it is set as fo(X), and the tool stand 9 is controlled accordingly. Furthermore, the position of the tool 13 with respect to the tool stand 9 is controlled according to the following formula: fI CO,

As Ya, in addition to using the average value of the maximum value and minimum value of Y as described above, it is also possible to use an average value such as the average of the sum of squares between θ:=0 and 2π.

By doing this, the formula for determining the position Y in the Y-axis direction of the tool 13 for turning an article of any shape can be determined by determining the position Y of the tool 13 in the Y-axis direction. The parts unrelated to θ and the parts related to θ can be determined in advance based on the target machining shape, so the data Alternatively, by inputting a calculation program into the computer 8, the positions of the tool stand 9 and the tool 13 can be controlled accordingly.

(Effect of the Invention) As is clear from the above description, according to the present invention, the position of the tool rest can be controlled in the X-axis direction and the Y-axis direction by the tool rest position control device, and the tool rest position can be controlled in the X-axis direction and the Y-axis direction. The position of the tool in the Y-axis direction relative to the table can be controlled by an electro-hydraulic servo mechanism, and among the control amounts of the tool position in the Y-axis direction,
The parts that need to be controlled at low speed regardless of the rotation angle of the spindle are controlled by the position of the tool rest, and only the parts that need to be controlled at high speed depending on the rotation angle of the spindle are controlled by the position of the tool relative to the tool rest. Since the bridge is provided, the hydraulic cylinder used in the electro-hydraulic servomechanism can have a small stroke, which reduces the weight of the moving parts and further improves high-speed response. become able to. Therefore, even when machining an article having a non-circular cross section, the rotational speed of the spindle can be increased, and the machine tool can have high machining efficiency and obtain a good finished surface.

Furthermore, when performing turning processing, normally the final target shape is obtained by performing small-scale turning several times, but the machine tool according to the present invention can control the return of the tool and the depth of cut in this case. However, the holder can be held by controlling the position of the tool stand, so even in such cases, the center of the reciprocating motion of the piston in the hydraulic cylinder can be maintained near the center of the hydraulic cylinder, achieving high machining accuracy. can be kept.

Furthermore, the machine tool for articles having a non-circular cross section according to the present invention utilizes an NC machine tool equipped with a tool rest feeding mechanism in the X-axis and Y-axis directions by means of a conventional pole screw, and has an electric current on the tool rest. This can be achieved simply by installing a hydraulic servo mechanism and supporting the tool so that the servo mechanism positions the tool. Therefore, it is easy to modify, and if necessary, the added electro-hydraulic servo mechanism can be stopped to hold the tool fixed, allowing it to be used in the same way as a normal NC machine tool. can do.

Note that the machine tool according to the present invention is not limited to one that processes the outer circumferential surface of a workpiece, but can also be applied to a machine tool that processes the inner circumferential surface of a cylindrical workpiece or performs face turning of an end surface, etc. . For example, in the above-mentioned machine tool, if the direction of the tool and the hydraulic cylinder installed on the tool stand can be rotated by 80 degrees, it becomes possible to process an uneven end face.

Furthermore, it is clear that the machine tool according to the present invention can be applied not only to lathes but also to grinders and the like. It is also applicable to a device in which the tool rest supporting the tool is fixed in the X-axis direction and the workpiece is moved in the X-axis direction.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an embodiment of a machine tool according to the present invention, FIG. 2 is a front view of the machine tool, and FIG. 3 is a view of an article having a non-circular cross section to be machined by the machine tool. FIG. 4 is an explanatory diagram illustrating the control amount for the processing. FIG. 5 is a side view and front view showing a specific example of the article to be processed. FIG. 6 is a tool stand and a tool. FIG. 2 is an explanatory diagram for determining each control amount. 1...NC lathe 3...Main shaft 4...Moving table 5...Feed screw B...Computer 9...Tool stand lO...Feed screw 11
...Servo motor 13...Tool 15.
...Hydraulic cylinder 16...Electro-hydraulic servo mechanism 19...Encoder

Claims (2)

[Claims] (1) With respect to the rotated workpiece W, when the direction parallel to the rotation axis O is the X-axis direction and the perpendicular direction is the Y-axis direction, it is installed so that it can move relative to the X-axis direction and the Y-axis direction. The tool stand 9 that has been
a tool rest position control device that relatively moves in the Y-axis direction by a predetermined size based on the target machining shape of the workpiece W; the tool 13, and the tool 13 at each position in the X-axis direction,
Target machining cross-sectional contour shape of the workpiece W and the tool stand 9
The tool stand 9 is moved by a predetermined amount corresponding to the rotation angle θ of the workpiece W by the amount of movement in the Y-axis direction.
electro-hydraulic servo mechanism 16 for moving in the Y-axis direction
A machine tool for an article having a non-circular cross section, comprising: (2) The amount of movement of the tool stand 9 in the Y-axis direction, which is moved by the tool stand position control device, is determined from the rotation axis O of the target machining cross-sectional profile of the workpiece W at each position in the X-axis direction. The machine tool according to claim 1, characterized in that it is defined by an average radius of .