JPS6146259B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a synchronous operation method for NC machine tools that require synchronous operation, such as numerically controlled hobbing machines.

In recent years, with advances in control technology, machine tools using numerical control (hereinafter referred to as NC machine tools) have become widely used.

For example, numerical control is being widely used in hobbing machines that perform gear cutting, and efforts are being made to improve production efficiency and quality. At the same time, there is also a demand for faster cutting speeds, making the design conditions for control systems more difficult. ing. In particular, for machines such as hobbing machines that require synchronization of the hob shaft and table drive shaft,
As the cutting speed increases, a cutting speed (speed of the table drive shaft) that is almost equal to the rapid traverse speed until cutting starts is required, and as in the past, the time constant and position, which are the basic factors of the control system, are required. It is no longer possible to set the loop gain in consideration of the steady state, that is, controlling the cutting feed rate, and the transient state, that is, controlling the rise, fall, etc. corresponding to the rapid feed speed, and it is necessary to perform synchronous operation with an NC hobbing machine, etc. In some cases, various problems occur.

The present invention was made in view of the current situation, and
The purpose of the present invention is to provide a method for synchronous operation of numerically controlled machine tools that improves cutting accuracy and enables synchronous operation without reducing cutting conditions. The present invention, which achieves this object, is a numerically controlled machine tool that rotates one rotary shaft synchronously with the start-up and steady state rotation of the other rotary shaft and performs machining in the steady state, and is ideal for machining in the steady state. When operating under the numerical control conditions in which a servo error occurs in synchronized operation at startup, control is performed to delay the startup of the other rotating shaft so that the one rotating shaft can be synchronized. .

Hereinafter, the method of the present invention will be explained in detail with reference to the drawings.

In addition to the axes that have only the so-called feeding function or positioning function of normal NC machine tools, namely the radial feed axis, hob shift axis, and axial feed axis, NC hobbing machines are equipped with a table drive axis that rotates in synchronization with the rotating hob axis. There is. Of these four axes, the other three axes except the table drive axis have a cutting feed rate of 0.1 in steady state.
~0.3 m/min, which is relatively small, whereas the rapid traverse speed, that is, the speed corresponding to the transient state, is, for example, 5 m/min.
m/min, and there is a considerable difference between the two speeds, so when designing the control system, the time constant during rapid traverse must be determined according to the moment of inertia and driving purpose so that the rise and fall are smooth. , there is no problem in controlling both speeds without considering the low speed portion during cutting feed. However, for the table drive axis, the cutting feed rate is expressed by the following formula:
As shown in (1), it is determined by the hob rotation speed, the number of hob openings, and the number of workpiece teeth, and currently it is 1 to 10.
It is said that the value is in the range of m/min, but when the speed of this table drive axis is calculated based on formula (1), the first
A curve as shown in the figure is obtained.

Table drive shaft speed/(m/min)=
Hob rotation speed (rpm) x number of hob openings/number of workpiece teeth x 360...(
1) On the other hand, the rapid traverse speed of the table drive axis is also 10m/mi.
n, and both speeds are at the same level. Therefore, if the time constant of the cutting feed is selected appropriately, it will affect the gear cutting accuracy. This is because the table drive shaft must be rotated in synchronization with the hob shaft, and since gear cutting is intermittent cutting, an intermittent load is applied to the table drive shaft, resulting in a time constant T _S that is the basis of NC control. This is because it is not possible to arbitrarily select the position loop gain _KP , which is a guideline for recovering the delay of the current value with respect to the NC command. Therefore,
As shown in Fig. 2, the left surface L and right surface R of the teeth of gear 1
The relationship between the machining accuracy of the tooth trace, the time constant T _S (msec), and the position loop gain K _P (rad/sec) was investigated.
As a result, as shown in Fig. 3a, b, and c, if the time constant T _S and position loop gain K _P are not carefully considered, the gear cutting accuracy is poor, and as shown in Fig. 4, If carefully examined, the gear cutting accuracy is also good. In this way, from Figures 3 and 4, the time constant T
It can be seen that _S and the position loop gain K _P affect the gear cutting accuracy.

On the other hand, NC hobbing machines also have the same problem of table lag as a characteristic inherent in NC equipment.
The delay of this table is as shown in Figure 5a.
Even if the hob 2 and workpiece 3 are positioned in a static state, their positions will shift in a dynamic state where the table is driven and the workpiece 3 is rotated.
In the figure, a changes to a'. Since this positional deviation naturally affects the gear cutting accuracy, it is preferable that it be small, and in particular when gear cutting is to be performed two or three times, it must be set so that this deviation becomes zero. Furthermore, it has been conventionally thought that this positional deviation, that is, the table delay amount Δ, is determined by the table drive shaft speed F and the position loop gain K _P , and reducing this delay amount Δ improves the gear cutting accuracy. This point was considered to improve the operating characteristics of the NC hobbing machine, but the inventors of the present application found that it is also closely related to the time constant T _S.
The delay amount Δ is expressed by the following equation 2, and the time constant T
We have come to know that there is an optimal value for _S and position loop gain K _P.

Δ=F/60(1/K _P +T _S )...(2) The value of this equation (2) is shown in FIG. 6 with respect to the table drive shaft speed F. In the figure, the position loop gain K _P is constant at 50 rad/sec, the time constant T _S is 80,
40, 40, 0 msec, and when the time constant T _S = 80 msec _, the accuracy is poor, and when T _S = 20 msec or less, it becomes difficult to control the speed of the table drive axis. This corresponds to the case where the time constant is ignored. Therefore,
The design condition for the time constant T _S is 20 to 40 msec. Also, from the viewpoint of gear cutting accuracy, the position loop gain K _P
The design condition is 50 to 100 rad/sec. However, the design conditions for this time constant T _S and position loop gain K _P are both upper limit values for NC machine tools. For this reason, if the rotation speed of the table drive shaft is around 5 m/min, it can be synchronized with the hob shaft even during normal startup or stop, but when the rotation speed approaches 10 m/min, the table drive shaft cannot start or stop. It is not easy and difficult to synchronize, that is, follow. That is, since the time constant T _S and the position loop gain K _P must be set to the fullest limit of the condition, the transient state at the time of starting and stopping the table drive shaft cannot be controlled, resulting in a servo error.

Therefore, to remove this servo error,
Control is performed to delay the rise and fall of the hob shaft when it starts and stops to the extent that the table drive shaft can be synchronized. Specifically, as shown in Fig. 7, the hob shaft speed H is increased or decreased in steps, and the table drive shaft speed F is synchronized with each step speed to achieve the required rotation. Create a program to control it so that Also, in Fig. 8, the hob axis and table drive axis are started simultaneously, rather than being controlled stepwise, that is, digitally to delay the rise time or fall time, as in Fig. 7. The speed is controlled to be slower than the conventional rise and fall indicated by broken lines in a continuous manner, that is, in an analog manner. By doing this, it is possible to easily synchronize the table drive shaft control system even if the design conditions are full. Conventionally, the rise time in the case shown in FIG. 8 is 3 to 5 seconds, but synchronization can be achieved by extending this time to about 5 to 7 seconds.

In this way, the hob shaft and the table drive shaft can be synchronized, so that the time constant T _S and position loop gain K _P can be set to optimal values in terms of gear cutting accuracy. However, even in this case, a delay amount Δ due to the positional deviation of the table occurs as shown in ^FIG . As the workpiece 3 rotates sequentially, the tooth trace of the workpiece 3 shifts accordingly, so measure this shift amount Δ ₁ and Δ ₂ in terms of rotation angle,
NC this value as a function of the speed of the table drive axis.
Determine the value for each hobbing machine, correct this value, and perform gear cutting. For this correction, K _P or T _S in equation (2)
Various methods can be considered, such as changing the displacement of the hob 2 in response to the deviation.

As described above in detail with the embodiments, according to the present invention, cutting accuracy can be improved and synchronous operation can be easily performed without reducing cutting conditions. If a program for delaying in steps is used, reliable operability can be obtained. On the other hand, when the speed is linearly delayed, the time required to reach the final target speed is short and the program is simple.

In addition, although the above explanation was made for NC hobbing machines, it is not limited to hobbing machines, but can also be used for thread cutting with NC lathes, etc.
Applicable to NC machine tools that require synchronous operation.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the number of workpiece teeth and table drive shaft speed, Figure 2 is an explanatory diagram of the gear cutting accuracy measuring section, and Figures 3 a, b, and c are a close examination of the time constant and position loop gain. Figure 4 is a graph showing the gear cutting accuracy when the time constant and position loop gain are carefully considered, Figure 5 a,
b is an explanatory diagram of the misalignment between the hob and the table, No. 6
The figure is a graph showing the relationship between table feed speed and table delay amount, FIG. 7 is an explanatory diagram of one specific example of the method of the present invention, and FIG. 8 is an explanatory diagram of another specific example. In the drawing, 1 is a gear, 2 is a hob, 3 is a workpiece,
a and a' are positions, K _P is a position loop gain, T _S is a time constant, L is a left surface, R is a right surface, F is a table drive shaft speed, and Δ, Δ ₁ and Δ ₂ are table delay amounts.

Claims (1)

[Claims] 1 A numerically controlled machine tool that performs machining in a steady state by rotating one rotary shaft in synchronization with the start-up and steady-state rotation of the other rotary shaft, and under the optimal numerical control conditions for steady-state machining, the start-up Synchronization of a numerically controlled machine tool, characterized in that when operating under the numerical control conditions in which a servo error occurs during synchronized operation, the start-up of the other rotating axis is controlled to be delayed so that the other rotating axis can be synchronized. how to drive.