JPH0248361B2 - - Google Patents

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, the present invention 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 rotor of rotary engines. Further, in a shaft joint or the like, if the shaft itself is processed to have a non-circular cross section, it can be made highly reliable.

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 if the target cross-sectional profile of the workpiece is a smooth closed curve. In such cases, machining using such a milling machine or the like is not only inefficient, but also has low machining accuracy. Conventionally, in such cases, it has been common to use a hydraulic copying lathe or the like that controls 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, numerical control (hereinafter referred to as
NC that can be controlled by
It is possible to use machine tools. In theory, NC machine tools can machine workpieces into any shape simply by 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 rotates 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 in a direction perpendicular to it (hereinafter referred to as the X-axis direction). Below, Y
It is designed to be moved in the axial direction.
As the moving mechanism, a servo motor and a ball screw are used for feeding in the X-axis direction and the Y-axis direction, respectively. When such a feed mechanism is used, highly accurate position control can be performed over a long distance of several hundred mm to several thousand mm. 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 control the position of the tool in the Y-axis direction using a conventional NC machine tool to machine an object with a non-circular cross section, the rotation speed of the main spindle must be reduced to less than a few revolutions per minute. It was not possible to make the tool position respond to the rotation angle of the workpiece. On the other hand, in order to ensure a good finished surface and machining efficiency, the number of revolutions of the spindle must be increased to 100 revolutions/
It is required that it be at least 1 minute. For this reason, it is actually difficult to process articles with non-circular cross sections using conventional NC machine tools.

In view of these circumstances, the present inventor proposed an NC machine tool in which the positioning of a tool in the Y-axis direction is performed by an electro-hydraulic servo mechanism (Japanese Patent Application No. 58-53905). Since such an electro-hydraulic servo mechanism is excellent in terms of high-speed response and power, an NC machine tool using this mechanism can efficiently process objects with non-circular cross sections. By the way, when the positioning of a tool is performed by an electro-hydraulic servomechanism in this way, it is most common that 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. If you use a long hydraulic cylinder,
It is possible to increase the stroke, but doing so increases the weight of the moving parts and increases the inertia, and also causes problems with the compressibility of the hydraulic oil in the cylinder, causing the response of the servo system to increase. Sexuality decreases. Moreover, in hydraulic cylinders,
There is also the problem that 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, there is a difference between the characteristics when the piston moves toward the end of the cylinder and the characteristics when it moves toward the center. for that,
When positioning a tool using a hydraulic cylinder, high-precision machining becomes difficult unless the center of reciprocation of the piston is always located near the center of the cylinder.

In this way, NC using electro-hydraulic servo mechanism
Even with machine tools, problems still remain when attempting to process with high precision an article that has a large difference between the minimum radius and the maximum radius of the target machining shape.

(Object of the Invention) The present invention was made in view of the above 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, the position of the tool rest only needs to be controlled at a relatively low speed, so 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, let us consider a case where an article as shown in FIG. 3, which has a non-circular cross section and whose cross-sectional shape changes in the axial direction, is to be turned using an NC lathe. As shown in the figure, if the distance from the central axis of the article is r, the angle from the reference plane including the central axis is θ, and the distance from the reference plane perpendicular to the central axis is x, then the target machining contour of the article The shape 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. Furthermore, the direction of x coincides with the X axis. Therefore, in order to turn a workpiece into the contour shape represented by r=f(θ, Y may be controlled so that Y=f(θ,x)+ _Y0 . Here, Y ₀ is
This is a constant representing the distance between the reference point for feeding in the Y-axis direction of the lathe and the rotation axis O 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 Y ₀ =0. Since there is no loss of generality in this way, in the following explanation,
Assume that Y ₀ =0. Further, the position X of the cutting edge of the tool in the X-axis direction is controlled so that X=x+X ₀ . Here, X ₀ 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 when X=0, in the following explanation, it is assumed that X ₀ =0.

In this way, when controlling the tool position separately in the X-axis direction and the Y-axis direction, in the X-axis direction,
should be satisfied. 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 by a feeding mechanism using a ball screw in a normal NC lathe.

In the Y-axis direction, Y=f(θ,x), that is, Y=
It must be controlled to satisfy 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
is the part f ₁ (θ,X) that changes depending on the rotation angle θ
and a portion f ₀ (X) that does not need to be changed depending on the rotation angle θ. That is, it can be set as follows: Y=f(θ, X)=f ₀ (X)+f ₁ (θ, X). If f ₀ (X) is appropriately selected, the amplitude of f ₁ (θ, X) can be made small. Moreover, f ₀ (X) generally changes slowly.

Therefore, in the present invention, the position of the tool stand in the Y-axis direction is controlled by f ₀ (X), and the tool supported on the tool stand so that it can reciprocate in the Y-axis direction is controlled by f ₁ (θ, )
It is controlled by

An example of a specific configuration for this purpose is shown in Figures 1 and 2.
As shown in the figure. In these figures, Figure 1 is a plan view showing an example of the NC lathe according to the present invention, and Figure 2 is a plan view showing an example of the NC lathe according to the present invention.
The figure is its front view.

As is clear from these figures, on the base 2 of this lathe 1, there is a
An axial linear motion guide surface 2a is provided,
A movable table 4 is slidably supported on this guide surface 2a. 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 using a step motor, the feed screw 5 is rotated by a step motor 7 driven by an oscillator 6, which generates a signal based on a command signal from a computer 8. Make it. Therefore, X of the moving platform 4
The axial position is always grasped by the computer 8.

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 O of the main shaft 3 of the lathe 1 . As shown in FIG.
A feed screw 10 in the Y-axis direction is rotatably supported, and a ball nut 9a provided on the tool stand 9 is engaged with the feed screw 10. The feed screw 10 is rotated by a servo motor 11 that operates based on a command signal from the computer 8. computer 8
is f ₀ (X) according to the position of the moving table 4 in the X-axis direction.
generates a signal proportional to the tool stand 9.
is moved by f ₀ (X) in the Y-axis direction.

On the tool stand 9, there is a linear motion guide surface 1 in the Y-axis direction.
2 is provided, and a tool holding member 14 that holds a tool 13 is supported along this guide surface 12 so as to be able to reciprocate. This tool holding member 14 is
The position in the Y-axis direction is controlled by a hydraulic cylinder 15 installed on the tool stand 9. The hydraulic cylinder 15 is a part of an electro-hydraulic servo mechanism 16, and the hydraulic pressure from the hydraulic source 18 is controlled by a servo valve 17 which is switched and controlled by a command signal from the computer 8. It's summery.

A rotary encoder 19 is attached to the main shaft 3 of the lathe 1, and the encoder 19 detects the rotation angle θ of the main shaft 3, and its detection signal is guided to the computer 8.
The computer 8 outputs a signal corresponding to f ₁ (θ, Control the electro-hydraulic servomechanism 16 to move the tool 13 to the tool stand 9 f ₁ (θ, X)
, in the Y-axis direction. The computer 8 outputs data of f ₀ (X) and f ₁ (θ, Alternatively, the values may be calculated and output according to a pre-installed program.

(Operation) Next, the operation 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, the tool 13 is positioned at the position of X=0, which is the reference plane of the target article. When the lathe 1 is operated in this state, as the workpiece W rotates, the computer 8 generates a signal corresponding to the rotation angle θ, and the hydraulic cylinder 1
5 is activated to control the position of the tool 13 in the Y-axis direction. 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 moving table 4 and therefore the tool table 9 in the X-axis direction,
The position X of the tool 13 in the X-axis direction changes. As a result, the computer 8 outputs _a signal corresponding to the current position f ₁ (θ, X) in the Y-axis direction
move only. Therefore, the position Y of the tool 13 in the Y-axis direction is controlled to be Y=f ₀ (X) + f ₁ (θ, X), and the workpiece W is turned into a predetermined shape.

For example, if the tool stand 9 is controlled as shown in FIG. 4a and the tool 13 is controlled as shown in FIG. 4b, the workpiece W is machined into the shape shown in FIG. 4c. In Figure b, the amplitude represents the stroke in which the tool 13 is reciprocated according to f ₁ (θ, X) while the workpiece W makes one revolution. 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 ball screw mechanism of a feed screw 10 and a ball nut 9a, and a servo motor 11. 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 FIGS. 1 and 2.

An article with a nearly triangular cross section and a taper in the axial direction, as shown in Figure 5, can be expressed using cylindrical coordinates as r=r ₀ +kx+a sin3θ (r ₀ , k, and a are arbitrary constants). Can be done. Therefore, in order to obtain an article having such a shape, the position Y of the cutting edge of the tool 13 in the Y-axis direction may be controlled so as to satisfy the following equation: Y=r ₀ +kX+a sin3θ. Therefore, if we separate this equation into a part f ₀ (X) that is unrelated to θ and a part f ₁ (θ, X) that is related to θ, we get f ₀ (X)=r _{0 +} k ,X)=a sin3θ.

In this way, f ₀ (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, the tool stand 9 is moved in the Y-axis direction by r ₀ +kX as it is moved in the X-axis direction.
Control is performed using a tool stand position control device consisting of a servo motor 11, a feed screw 10, and a ball nut 9a.

On the other hand, f ₁ (θ,
Its control requires high-speed response. Therefore,
The main shaft 3 is controlled by an electro-hydraulic servo mechanism 16 and detected by an encoder 19.
The tool 13 moves in synchronization with the rotation angle θ of a sin3θ
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 spindle 3, and the part f ₀ (X) = r ₀ +kX, which needs to be controlled according to θ. By separating the part f ₁ (θ, X) = a sin3θ and controlling only the part f ₁ (θ, The center position of the amplitude of the hydraulic cylinder 15 at 16 becomes constant, and cutting is performed under substantially the same conditions regardless of the position X in the X-axis direction. In addition, the hydraulic cylinder 1
5 can be a hydraulic cylinder that only needs to have a stroke of 2a, has a short effective operating range, and has a small weight of movable parts. On the other hand, if we try to control the entire position of the tool 13 in the Y-axis direction using a single hydraulic cylinder, that hydraulic cylinder would need a stroke of 2a+kh (h is the length of the target object). becomes.

_The formula Y = (θ _, θ,
If it cannot be easily separated into X), consider the cross-sectional shape of the target workpiece at each position Xi in the X-axis direction. Its cross-sectional profile is a closed curve as shown in FIG. 6, represented by f(θ, Xi). Therefore, the average radius from the central axis of the cross-sectional contour, that is, Y in the Xi section
Find the average value of the maximum and minimum values. Letting the average value be Ya (Xi), Y (θ, Xi) = Ya (Xi) + {f (θ, Xi) - Ya (Xi)}.

Therefore, such an average value Ya(Xi) is
If each position in the X-axis direction is determined, 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 f ₀ (X), and the tool stand 9 is controlled accordingly. Also, as f ₁ (θ, X) = f (θ,
control the position of

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 value 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 calculated using a formula that is not related to the rotation angle θ of the main shaft 3. and a part related to θ. These parts unrelated to θ and parts related to θ can be determined in advance based on the target machining shape, so by inputting that data or calculation program into the computer 8, the tool stand can be 9 and tool 13 can be controlled accordingly.

(Effects of the Invention) As is clear from the above description, according to the present invention, the position of the tool rest is controlled by the tool rest position control device.
In addition to controlling the tool position in the axial direction and the Y-axis direction, the position of the tool in the Y-axis direction with respect to the tool rest can be controlled by an electro-hydraulic servo mechanism. 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 by the rotation angle of the spindle are controlled by the position of the tool relative to the tool rest. As a result, the hydraulic cylinder used in the electro-hydraulic servo mechanism can be used with a small stroke, reducing the weight of moving parts and further improving high-speed response. become. 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 with the machine tool according to the present invention, the return of the tool and the amount of cut in that case are control can also be taken over by controlling the position of the tool stand, so even in such cases, the center of the reciprocating motion of the piston inside 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 direction and Y-axis direction using an ordinary ball 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 servomechanism can be stopped to hold the tool fixed, making it work just like a normal NC machine tool. It can be used for.

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 90 degrees, it becomes possible to process an uneven end surface.

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 drawings]

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,
FIG. 3 is an explanatory diagram of an article having a non-circular cross section that is machined by the machine tool, FIG. 4 is an explanatory diagram that explains the control amount for the machining, and FIG.
A side view and a front view showing a specific example of an article to be processed, and FIG. 6 are explanatory diagrams for determining each control amount of the tool stand and the tool. 1... NC lathe, 3... Main spindle, 4... Moving table,
5...Feed screw, 8...Computer, 9...Tool stand, 10...Feed screw, 11...Servo motor, 13...Tool, 15...Hydraulic cylinder, 16
...Electro-hydraulic servo mechanism, 19...Encoder,
O...rotation axis, W...workpiece.

Claims (1)

[Claims] 1. Relative to the X-axis direction and the Y-axis direction when the direction parallel to the rotating axis O of the workpiece W to be rotated is the X-axis direction and the perpendicular direction is the Y-axis direction. A movably installed tool stand 9 and the tool stand 9 are moved relative to each other in the Y-axis direction by a predetermined size based on the target machining shape of the workpiece W at each position in the X-axis direction. A tool stand position control device for moving the workpiece W; a tool 13 supported on the tool stand 9 so as to be able to reciprocate in the Y-axis direction; and a tool 13 that moves the tool 13 at each position in the X-axis direction. The Y-axis relative to the tool stand 9 is adjusted by a predetermined amount corresponding to the rotation angle θ of the workpiece W based on the target machining cross-sectional contour shape and the amount of movement of the tool stand 9 in the Y-axis direction. An electro-hydraulic servomechanism 16 for moving an article in a direction. 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 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.