KR830002245B1 - How to control cutter feed speed - Google Patents

Abstract

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Description

How to control cutter feed speed

1 is a graph showing the output-speed characteristics of a motor.

2 (a) to 2 (d) are diagrams describing a cutting method by controlling the circumferential speed of a workpiece at a constant value according to the conventional art.

3 (a) to 3 (e) are diagrams describing a cutter feed speed control method according to the present invention.

4 is a circuit block diagram of a cutter feed speed control method according to the present invention.

5 is a flow chart illustrating a cutter feed speed control method according to the present invention.

6 is another circuit block diagram for controlling a cutter feed speed according to the present invention.

The present invention relates to a method for controlling the feed rate of a cutter, in particular constant torque and constant output characteristics for driving the spindle so that the machine tool can cut the workpiece while the circumferential speed of the workpiece is kept constant by the motor. A cutter feed rate control method suitable for a machine tool in which the motor having an operating zone of is used.

Cutting on machine tools, in particular lathes, is carried out with a controlled circumferential speed of the workpiece. The cutting of the workpiece through this method of circumferential speed control has the following advantages.

(1) Smoothness and gloss of the workpiece surface are improved.

(2) The machining time (cutting) is shortened.

(3) The cutting amount may be constant.

The output power P (KW) of spindle motors used in machine tools such as lathes rises linearly until a certain speed (referred to as the basic speed) Nb is maintained and then maintains a constant maximum Pmax.

Since the cutting amount Q depends on the spindle motor output P, the cutting amount Q becomes maximum at the basic speed Nb or more and becomes constant at the maximum value Qmax but decreases with a speed smaller than Nb.

In the control method to maintain a constant circumferential speed, the larger the outer diameter of the workpiece is, the smaller the spindle speed Ns becomes. In order to maintain a high cutting speed, the conventional method of cutting a workpiece with a large outer diameter does not cut at the maximum cutting amount Qmax based on the maximum output of the spindle motor. It was. It calculates the motor output P (less than Pmax) corresponding to the minimum spindle speed to first obtain the minimum spindle speed determined by the maximum outer diameter Dmax of the workpiece, and finally the cutting amount Q (less than Qmax) determined by this output P Was to get. Therefore, cutting is a problem of determining the cutter feedrate fr to satisfy the cutting amount Q and feeding the cutter according to this feedrate fr.

However, in this conventional cutting method, the motor or spindle speed Ns eventually exceeds the basic speed Nb due to the progressive reduction in the workpiece diameter as the machining proceeds. Thus, although the cutting conditions allow the cutting to advance at the maximum cutting amount Qmax, the method described above constrains the machining to proceed at a constant cutting amount. As a result, cutting according to the conventional method of circumferential speed is inconvenient because it does not maintain the advantage of sufficient utilization of the spindle motor output given by constant circumferential speed control and does not satisfactorily shorten the machining time. Therefore, the cutter feedrate control device requires a device capable of cutting at the maximum cutting amount Qmax even if the workpiece has a large outer diameter. In other words, there is a need for a device that can make the best use of the spindle motor output.

Accordingly, an object of the present invention is to cut at the maximum cutting amount Qmax when the speed of the spindle is faster than the reference speed, that is, to feed the cutter at the maximum feed rate and to reduce the cutting amount according to the spindle speed when the spindle speed is lower than the reference speed. It is to provide a cutter feed speed control method for performing cutting by cutting, that is, by making the most of the spindle motor output made by reducing the cutter feed rate.

Another object of the present invention is a cutter feed rate control method for shortening the cutting time for a workpiece having a large outer diameter by increasing the cutting amount when the outer diameter of the workpiece decreases, that is, as the spindle speed increases as the machining proceeds. To provide.

It is still another object of the present invention to provide a cutter feed rate control method in which the radius of a workpiece is simply remotely controlled and the spindle motor output can be fully utilized.

BEST MODE Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a graph describing the output characteristic (output-speed characteristic) of the motor, in which the output P of the motor is increased linearly until the spindle speed reaches the Nb value, and then the output level is set to a constant value Pmax. Keep it. Although not shown, the torque τ is related to the output P and the motor or spindle speed Ns and the equation P = KxNs × τ (K: 1.0269), which is constant until the spindle speed reaches Nb and then inversely proportional to the speed Ns. The constant output and constant torque zones are considered constant output and constant torque characteristic zones, respectively, and the spindle speed Nb, which varies from the constant output characteristic zone to the constant torque characteristic zone, is considered the basic speed.

The amount Q cut by the cutting tool depends on the output of the spindle motor and can be kept constant at a large value of Nb or more with respect to the spindle speed even if it decreases to a speed below Nb depending on the spindle speed. The constant output characteristic area is typically 2/3 to 3/4 of the full range of motor speeds.

When the circumferential speed is constant, the spindle speed Ns is represented by the following equation.

Ns = Vc /? D... … (One)

Where Vc is the circumferential speed, D is the diameter of the workpiece, and as the outer diameter D increases, the spindle speed Ns decreases. When the outer diameter of the workpiece exceeds an arbitrary value, Ns falls below the basic speed Nb.

Workpieces with large outer diameters cannot be cut at the maximum cutting amount Qmax determined by the maximum motor output Pmax. Therefore, in order to control the cutting amount to be constant while the circumferential speed is similarly controlled, the conventional method calculates the motor output P corresponding to the minimum spindle speed determined by the maximum outer diameter Dmax of the workpiece, and the cutting amount Q determined by the output P. After finding (<max), the cutter feedrate fr is determined to satisfy this cutting amount. However, as the machining proceeds, the outer diameter of the workpiece gradually decreases, so that the machining can be performed at the maximum cutting amount Qmax since the spindle speed eventually exceeds the basic speed. However, unfortunately, in the above state, the change of the cutting amount Q cannot be achieved by the conventional method, and the workpiece cannot be cut by fully utilizing the motor output. However, when the minimum spindle speed determined by the maximum outer diameter Damx is larger than the basic speed Nb by the conventional method, cutting can be performed at the maximum cutting amount Qmax. In other words, in the conventional method, when the basic speed Nb is lowered (when the constant output characteristic region is widened) or the maximum outer diameter Dmax of the workpiece is reduced, the time portion during which machining is performed at the maximum cutting amount Qmax becomes large. The conventional cutting method is shown in Figs. 2 (a) to 2 (d), and in the second (a) diagram illustrating the coordinates of the work W and the cutting direction (arrow A) of the cutter T, The cutter T and the work W are displayed. In particular, the center of the workpiece is located at the origin (X = 0) and the end is located at the coordinate X ₁ (Dmax = X ₁ ). FIG. 2 (b) describes how the motor or spindle speed Ns is related to the cutter position, that is, the outer diameter of the workpiece. Therefore, the outer diameter of the work W decreases as the cutter T advances, and the spindle speed Ns (= Vc /? D) increases. When the diameter of the workpiece W decreases, the spindle speed Ns becomes large even though not larger than the constant speed Nmax due to the characteristics of the motor, and is stabilized as Namx at X = X ₂ . Figure 2 (c) shows the circumferential (cutting) speed Vc (= π · Ns · D) indicated for the cutter position, where the circumference when the outer diameter of the workpiece W is small after the spindle speed Ns reaches Nmax The speed Vc decreases linearly. Finally, Fig. 2 (d) shows the cutting volume band cutter position from which the magnitude of Q at the minimum value of the spindle speed Ns determined by Vc / πmax when the outer diameter of the workpiece has its maximum value is determined by the motor output P. You can see that it depends.

Therefore, it can be seen from the foregoing that the cutting amount is determined by the motor output P (less than Pmax) when the outer diameter of the workpiece is maximum, so that the conventional method of circumferential speed control is defective.

This means that the cutting amount cannot be changed even when the motor output reaches the Pmax value as the machining progresses, so that the output of the motor cannot always be fully utilized.

The basic principle of the invention will be understood from FIG. 3, which illustrates the interrelationship of the motor or spindle speed Ns, the circumferential speed Vc, the cutting amount Q, the cutter feed rate fr and the cutter position or the radius of the workpiece. In this figure, the dotted line shows the curve of the conventional method.

As in the conventional method described above, the cutting amount Q is fixed by the motor speed and the motor output characteristics when the outer diameter of the workpiece has its maximum value, which is a drawback of the prior art which negates the full utilization of the motor performance, and the machining proceeds. This results from the fact that the cutting amount Q cannot change when the outer diameter of the workpiece decreases.

However, as the outer diameter of the workpiece gradually decreases due to the cutting process, when the cutting amount is enlarged in accordance with the motor output characteristics, it is possible to fully utilize the motor performance, thereby cutting at a constant circumferential speed.

Nb인 영역에서 최대 절삭량 Qmax의 일정량이 되도록 제어됨으로써 모우터 성능의 충분한 사용이 성취된다. 절삭량 Q는 하기식으로 표현될 수 있다.In general, there is a proportional relationship between the motor output P and the cutting amount Q, so that as the outer diameter of the workpiece decreases with a spindle speed Ns (Ns <Nb) less than the reference speed Nb, that is, as the Ns increases, the cutting amount Q is proportional to Ns. Zoom in by Ns

Sufficient use of the motor performance is achieved by being controlled to be a constant amount of the maximum cutting amount Qmax in the region of Nb. The cutting amount Q can be expressed by the following formula.

Q = frd Vc... … (2)

Where Vc is the circumferential speed, d is the cutter width, and fr is the feed rate of the cutter, respectively.

When the spindle speed Ns is larger than the reference speed Nb, the cutting amount Q is estimated to be a constant value Qmax determined by the maximum output Pmax of the motor. Therefore, the maximum cutter feed rate fr _max for obtaining Qmax is determined from the following equation.

fr _max = Q _max / d Vc... … (3)

Nb에 대하여 fr_max로 일정하게 유지되어야 하지만 Ns

Nb에 대하여는 Ns에 비례하여야 한다. 그리고, 최초의 절삭량 Q는 최대 공작물직경시에 모우터 속도 및 모우터 출력 특성으로부터 유도되어야 하며, 그후 (2)식으로부터 얻은 이송속도 fr(=Q₀/d·Vc)은 최초 이송 속도 fr₀로서 취해진를 따라서 본 발명의 특징에 따라서 fr_max가 (3)식으로부터 얻어저 커터 이송속도Where d is a constant determined by the dimensions of the cutter, and since the circumferential speed Vc is not set once to obtain good surface smoothness and glossiness, once set, it takes a sufficient advantage of motor performance along the amount that does not change. For cutting at the circumferential speed Vc, the feedrate fr of the cutter is Ns

It should remain constant with fr _max for Nb, but Ns

For Nb it should be proportional to Ns. Then, the initial cutting amount Q should be derived from the motor speed and motor output characteristics at the maximum workpiece diameter, and then the feed rate fr (= Q ₀ / d · Vc) obtained from equation (2) is the initial feed rate fr ₀ According to the characteristics of the present invention taken as follows, fr _max is obtained from equation (3)

일 때는 최대 커터 이송 속도 fr_max를 송출하고 Ns<Nb일 때는 조작 fr_max·

를 행함으로써 응답한 후 전술한 조작의 결과에의존하는 fr_max또는 fr_max·

가 될 커터 이송 속도 지정 fr 의 형태로 지령신호를 공급하는 이송속도 지령회로(FRC)와, 이송 속도 지령 fr에 응답하며 커터 구동 모우터(MT)의 속도를 제어하기 위한 속도 제어회로(VC)와, 연산 조작 진행과 전술한 회로의 조작 타이밍에 따라 상기 장치들을 제어하기 위한 제어기(CN)로 구성된다. 상기 속도 제어회로(VC)는 X방향으로 이동하는 커터의 거리를 구속하는 도시하지 않는 종이 테이프와 같은 매체로부터 얻은 X방향 지령치 Xc 및 커터 이송 속도 지령 fr을 기준하여 펄스를 인터플 레이트(interpolate)하여 그 주파수가 지령률 fr에 일치 하는 펄스 열 Xp를 송출하는 펄스 인터플레이터(PDC)의 펄스 Xp가 발생될 때마다 (커터가 양의 방향으로 이동하는 것을 제외하고) 그 내용이 증분되며 커터 이동의 전술한 거리에 응답하여 귀환 펄스 Fp가 발생될 때마다 감분되며, 이렇게 계수기 내에 기억된 값이 위치 편차 e, 특히 커터 이동의 실재량과 커터가 임의 위치로 이동하도록 지시된 양 사이의 차이와 동등한 가역 계수기(RCN)와, 위치 편차 e에 비례하는 애널로그 전압을 발생하기 위한 디지탈 애널로그 변환기(DA) 및 증폭기(AMP)를 가진다. 본 방법은 또한 모우터(MT)가 특정한 정도의 회전을 할때마다 즉, 커터가 전술한 거리를 이동할 때마다 단일 귀환 펄스 Fp를 발생하도록 커터 구동 모우터(MT)의 축상에 설치된 로우러리 엔코우터(REC)를 포함한다.A circuit block diagram for achieving the present invention as described above is shown in FIG. This method stores the current position of the cutter as the distance from the center of the workpiece, the contents of which are incremented or decremented by the pulse FP generated each time the cutter is moved in the radial direction of the workpiece. The operation stores the X-register (XR), which depends on the direction of the cutter movement, the circumferential speed Vc and the current position X of the cutter, i.e. information about the radius of the workpiece, to calculate the speed Ns of the spindle drive motor. Computes the calculation circuit (RVC) that responds by calculating Vc / 2πx, the comparator circuit (COM) for comparing the magnitude of the motor speed Ns with respect to the basic speed Nb, and indicates the circumferential speed Vc, the cutter width d, and the maximum cutting amount Qmax. The maximum cutter feed rate calculation circuit (MFRC) for storing the information to be stored and calculating and responding to the maximum cutter feed rate fr _max (= Q _max / Vc · d), and the register (FRR) for storing the maximum cutter feed rate r _max . With Ns, Nb, fr _max signal and information indicating the comparison result applied by the comparator (COM)

Is sent the maximum cutter feed rate fr _max , and when Ns <Nb, operation fr _max

Responds by doing the following: fr _max or fr _max depending on the result of the above operation

Feed speed command circuit (FRC) for supplying a command signal in the form of cutter feed speed designation fr to be, and speed control circuit (VC) for controlling the speed of the cutter drive motor (MT) in response to the feed speed command fr. And a controller (CN) for controlling the devices in accordance with the operation operation progress and the operation timing of the circuit described above. The speed control circuit VC interpolates pulses on the basis of the X-direction command value Xc obtained from a medium such as a paper tape (not shown) that restrains the distance of the cutter moving in the X direction and the cutter feed speed command fr. Each time a pulse Xp of a pulse interflater (PDC) that sends a pulse train Xp whose frequency corresponds to the command rate fr is generated, its contents are incremented (except that the cutter moves in the positive direction) and the cutter Each time feedback pulse Fp is generated in response to the aforementioned distance of movement, it is decremented, so that the value stored in the counter is the difference between the position deviation e, in particular the actual amount of cutter movement and the amount instructed to move the cutter to an arbitrary position. And a reversible counter (RCN) equal to and a digital analog converter (DA) and an amplifier (AMP) for generating an analog voltage proportional to the position deviation e. The method also includes a roller encoder installed on the axis of the cutter drive motor MT to generate a single feedback pulse Fp whenever the motor MT makes a certain degree of rotation, ie whenever the cutter travels the aforementioned distance. Include a woofer (REC).

The method of FIG. 4 works as follows. Initially, the maximum cutter feed rate fr _max is determined in the calculation circuit (MFRC) using the formula (3) and then stored in the register FRR, and the speed Ns of the spindle drive motor is the workpiece radius (stored in the X register (XR)). By the calculation circuit RVC.

Nb나 또는 Ns>Nb를 이송 속도 지령회로(FRC)에 송출하는데, 이 이송속도 지령회로(FRC)는 NsNb일때는 커터 이송속도 fr_max로 Ns<Nb일때는 fr_max·

로 커터 이송 속도를 나타내는 지령신호 fr를 속도 지령회로(Vc)에 공급함으로써 응답한다. 속도 제어회로(Vc)는 이 지시에 응답하여 커터 이송속도를 제어한다. 특히, 펄스 인터를레이터(RDC)는 X 방향 지령치 Xc 및 이송속도 지령 fr을 기준하여 펄스 인터플레이터를 행하며 가역 계수가(RCN)에 펄스 Xp의 열을 공급한다. 그후 계수기의 디지탈 내용은 커터(도시하지 않은)를 이동시키는 커터 구동 모우터(MT)를 동작하기 위해 순차적으로 증폭되는 애널로그 양으로 변환된다. 모우터(MT)가 규정된 회전수로 회전할때 로우러리 엔코우더는 가역계수기(RCN)내에 기억된 값을 감분하는 귀환 펄스 Fp를 인출한다. 이 귀환 펄스 Fp도 X레지스터(XR)에 인가되어 커터가 각각 양 또는 음 방향으로 이동되었는지에 의존하여 기억된 값을 증분 또는 감분한다. 따라서 전술한 조작의 반복은 커터가 항상 이송 속도 지령 fr에 따라 이송되게 한다.Even if the contents of the X register XR are not equal to the radius of the workpiece before the workpiece and the cutter contact, it does not cause any inconvenience because the cutting operation has not yet started at this stage. Next, the comparator (COM) compares Nb and Ns, and the comparison result Ns

Nb or Ns> Nb is sent to the feedrate speed command circuit (FRC), which is the cutter feedrate fr _max when NsNb and fr _max when Ns <Nb.

It responds by supplying the command signal fr indicating the cutter feed speed to the speed command circuit Vc. The speed control circuit Vc controls the cutter feed speed in response to this instruction. In particular, the pulse interleaver RDC performs a pulse interflater on the basis of the X-direction command value Xc and the feed rate command fr, and supplies the heat of the pulse Xp to the reversible coefficient RCN. The digital contents of the counter are then converted into analogue amounts that are sequentially amplified to operate the cutter drive motor MT, which moves the cutter (not shown). When the motor MT rotates at the prescribed speed, the roller encoder draws a feedback pulse Fp which decrements the value stored in the reversible counter RCN. This feedback pulse Fp is also applied to the X register XR to increment or decrement the stored value depending on whether the cutter is moved in the positive or negative direction, respectively. Therefore, the repetition of the above operation causes the cutter to be always conveyed in accordance with the feed rate command fr.

The cutter feed rate control method according to the present invention will be clearly understood from the FIG. 5 flow charge.

Although the present invention has been described with respect to an embodiment in which a calculation circuit is installed to calculate the maximum cutter feed speed fr _max , this value is a constant obtained in advance by suitable means once the roller characteristics, the cutter width d and the circumferential speed Vc are determined. This value is introduced by means such as tape and stored in a register located in the speed command circuit. The apparatus of FIG. 4 includes hardware independent apparatuses for performing arithmetic and comparison operations, and the present invention can be realized by utilizing a processing apparatus such as a microcomputer.

Such an example is illustrated in FIG. 6, and parts compatible with those in FIG. 4 denote the same reference numerals, and description thereof will be omitted.

The apparatus of FIG. 6 includes a control processing unit (CPU), a storage unit (MEM) for storing the results and data of calculation operations, a storage unit (PR) for storing a processing program programmed according to the flower art of FIG. And an interfacing ADP ₁ , ADP ₂ and a feed speed control circuit VC provided between the sub control circuits. The memory MEM and the program memory PR can be used jointly.

The present invention provides a method that allows the motor's performance to be utilized to the maximum possible while maintaining the constant circumferential speed of the workpiece and provides a way to significantly shorten the cutting time, so that the workpiece is not limited by any limitation imposed by the diameter of the workpiece. Because it can be processed, it can be expected to be economical, especially when used on lathes.

Claims (1)

The feedrate of the cutter used in a machine tool of the type in which the spindle is rotated by a motor having a constant torque and a constant output operating range to maintain a constant circumferential speed of the workpiece while the workpiece is in motion by moving the cutter. In the controlling method, storing the maximum cutting amount Qmax determined by the maximum output Pmax of the motor, the maximum cutting feed speed fr _max calculated from the cutting width d of the cutter and the circumferential speed Vc of the workpiece, and D is the workpiece Calculating the spindle speed Ns from the equation Ns = Vc / πD at outer diameter, and the spindle speed Nb and the spindle speed Ns defined as the spindle speed where there is a shift from the constant torque application of the motor to the constant output area. Comparing the

When the feed rate fr _max , and when Ns <Nb, the cutter feed rate control method characterized in that the step of feeding the reduced feed rate cutter according to the spindle speed Ns.

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