JPH0223285B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a turning control device, and more particularly to a turning control device that does not damage threads or reduce the dimensional accuracy of screws even when the spindle speed is varied.

In turning operations such as thread cutting, gear grinding, gear cutting, etc., it is necessary to move the blade or workpiece in synchronization with the rotation of the main shaft. For example, in thread cutting, if the rotation of the spindle and the movement of the blade in the Z-axis direction are not synchronized, the dimensional accuracy of the thread may decrease, or a double thread may be formed during finishing, or the thread may become loose. I get saved up. For this reason,
The cutter starts moving in the Z-axis direction in synchronization with a one-rotation signal generated every time the main spindle rotates, and the rotation of the main spindle and the feed of the cutter are synchronized.

In addition, when changing the turning speed in the Z-axis direction between rough machining and finishing machining, change the rotation speed of the spindle at the same ratio to prevent double threads from being formed during finishing machining or the screw threads becoming loose. I try not to get caught.

By the way, in conventional turning processing, as shown in FIG. 1, the pulse distribution calculation for moving the blade is started based on the one-rotation signal RTP from the main spindle in order to determine the cutting position of the blade.
Moreover, for example, the distribution start instruction signal ITP is synchronized with the third sampling pulse SP ₃ after the generation of RTP.
can be generated, and a processing time Δδ for the distribution calculation that is longer than the sampling period ΔT can be secured.

However, since RTP is generated out of synchronization with sampling pulse SP, the length of time Δδ varies within the range of ΔT. Therefore, even if the delay of the servo system can be ignored, if the spindle rotational speed N differs, the cutting position will shift and a double thread will be formed.

For example, the spindle rotation speed for rough machining is set to Nc (rev/
sec), finishing rotation speed Nf (rev/sec)
(>Nc), the positional deviation caused by the fluctuation of time Δδ is expressed as 2π(Nf−Nc)·Δδ (1).

The above discussion does not take into account the delay in the servo system, but in reality, the delay in the servo system must also be taken into account. Now, considering that the position control system of the servo motor is a first-order delay system, this delay time Td is Td=1/G (where G is the gain), and is a constant time that does not depend on the rotation speed of the main shaft.

Therefore, when considering the delay time Td in addition to Δδ, a difference of Δθ=2π(Nf−Nc)(Δδ+Td) (2) occurs between rough machining and finishing machining. Furthermore, in reality, if the rotational speeds of rough machining and finishing machining are different, the sampling period ΔT may be changed in order to secure the processing time, and therefore the time Δδ itself that depends on the sampling period ΔT also differs. For this reason, in the conventional turning method, if the cutting speed is changed between rough machining and finishing machining, high-precision turning machining cannot be performed. Therefore, when high-precision turning is required, machining is performed by matching the rough machining speed Nc to the finishing machining speed Nf in order to make Δθ in the above equation (2) zero.

However, since finishing machining is performed at a lower speed than rough machining, machining efficiency deteriorates.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a turning control device that can perform highly accurate turning even when the spindle rotational speed is varied during rough machining and finish machining. The purpose of this invention is to perform a pulse distribution calculation in synchronization with a sampling pulse of a constant period ΔT after the generation of a one-rotation signal that is generated every time the spindle rotates once, and to move the cutter relative to the workpiece in the Z-axis direction. In a turning method in which the workpiece is moved and subjected to turning processing, the generation timing is changed so that the sampling pulse is generated when a time period of n·ΔT (n is an integer) has elapsed after the generation of the one-rotation signal. At the same time, when the turning speed in the Z-axis direction is Fz and the delay time of the servo system is Td, the cutter is moved relative to the workpiece in advance by Fz (n・ΔT+Td), and the one rotation signal mentioned above is generated. Then n・ΔT
This is achieved by a turning method in which pulse distribution calculations are performed in synchronization with sampling pulses generated over time, and the cutting tool is moved relative to the workpiece to perform turning processing.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIGS. 2 and 3 are schematic illustrations of the present invention.

Now, before turning starts, the cutter TB is stopped at a distance (referred to as approach distance) l from the workpiece WK. In this state, after one rotation signal RTP is generated from the spindle, the cutter TB moves by an approach distance l, and the workpiece rotates together with the spindle.
Turning begins when WK is reached. The time required for this approach (approach time) includes the stagnation time (Δδ + Td) until the tool starts moving, so if the spindle rotation speed is high, the time required for this approach (approach time) is longer than when the spindle rotation speed is low. The deviation in the rotation angle of the spindle from the generation of the rotation signal until the start of machining becomes large. In other words, the influence of this stagnation time on the cutting angle varies depending on the rotational speed of the spindle. Incidentally, the approach time that determines the shift in the angle of rotation is the sum of the stagnation time and the actual travel time, that is, Δδ+Td+(l/Fz). Therefore,
As shown in Fig. 2, if the approach distance from the generation of the one-rotation signal to the start of turning during high-speed rotation is made smaller by d compared to the approach distance l during low-speed rotation, The turning start positions can be made equal at low speeds.

The turning control device of the present invention has a position rotation signal RTP.
The time from the generation of the distribution start instruction signal ITP to the generation of the distribution start instruction signal ITP is controlled to be constant, for example, n・ΔT, and the cutter is Work TB
Move the cutter by d=Fz・(n・ΔT+Td) (3) in advance in the WK direction, and then move the cutter from that position after one rotation signal is generated to calculate the deviation of the cutting start position shown in equation (2) above. This is to correct Δθ.

FIG. 3 is a time chart for setting Δδ=n·ΔT (n=3). The time Δt from the generation time t ₀ of the one-rotation signal RTP to the generation of the first sampling pulse SP ₁ is measured. Then, after the time ΔT has elapsed since the generation of the sampling pulse SP ₁ , the second
At the same time _{, a soft timer (not shown) is set to (2・ΔT−Δt), and after (2・ΔT−Δt) has elapsed, a third sampling pulse SP 3 is} generated, and thereafter the soft timer is set to ΔT. By constantly setting the sampling pulses SP 4 , SP 5 . . . , it is possible to generate the sampling pulses SP ₄ , SP _{5 . .} . and to set Δδ=3·ΔT.

FIG. 4 is a block diagram of an embodiment of the present invention in which the stop position of the cutter before starting thread cutting is corrected in accordance with the spindle rotation speed.

Normally, the cutter BT is stopped at a position l (see Fig. 2) from the tip of the workpiece WK before starting thread cutting. Now, a pulse coder PC is attached to the shaft of the spindle motor SM that rotates the workpiece, and this pulse coder PC is connected to the spindle motor SM.
One pulse PS is generated each time the SM rotates by a predetermined angle, and one rotation pulse RTP is generated each time the main shaft motor SM rotates once. Speed detection unit VD
detects the rotation speed N (rev/s) of the main shaft motor SM by counting the number of pulses PS generated during a certain period of time, and sends this rotation speed N (rev/s) to the Z-axis movement speed calculation unit ZMV. input. Z-axis movement speed calculation section
In addition to the rotational speed N (rev/sec), the screw pitch LYmm/rev) is input to the ZMV from an NC device (not shown), and the calculation of Fz=L・N (mm/sec) is performed to determine the Z-axis direction. Calculate and output the moving speed Fz. Position correction calculation unit PCC is the movement speed
Fz is input, and Δδ(=n・
The calculation of equation (3) is performed using ΔT) and Td to generate a position correction value d, and this position correction value d is input to the pulse distributor PDC via the gate GT. When the position correction value d is input, the pulse distributor PDC performs pulse distribution in synchronization with the sampling pulse SP generated from the sampling pulse generator SPG to generate a distributed pulse, and inputs this distributed pulse to the servo circuit SVZ. and Z-axis feed motor MZ
to drive. As a result, the cutter approaches the workpiece by a distance d and stops. With the above operations, the position correction is completed, and then the gate GT is set to the screw pitch L.
(mm/rev) is input to the pulse distributor PDC. In this way, even if pulse distribution calculation is started in synchronization with sampling pulse SP ₃ after the one-rotation signal RTP is generated from the pulse coder PC, it will be driven with the pulse distribution every time the pulse PS from the spindle motor SM is generated thereafter. The Z-axis feed motor MZ does not match the rough machining speed Nc with the finishing machining speed Nf, and Δθ in equation (2) above becomes zero, and the spindle motor
Accurate thread cutting is performed by a blade that moves in synchronization with the speed N of the SM.

As described above, according to the present invention, even if the rotational speed of the spindle motor and the Z-axis direction movement of the cutter are changed, the thread cutting position can be made equal, and therefore the turning speed can be changed between rough machining and finishing machining. High-precision turning can be performed without forming double threads or crushing threads.

Although only the delay of the servo system was considered as the delay time Td, if an acceleration/deceleration circuit is provided after the pulse distributor, the delay due to acceleration/deceleration is included in the delay time.

[Brief explanation of drawings]

Figure 1 is a time chart explaining conventional turning processing, Figure 2 is an explanatory diagram explaining the present invention, and Figure 3 is an explanatory diagram explaining the present invention.
The figure is a time chart for setting Δδ=n·ΔT, and FIG. 4 is a block diagram of an embodiment of the present invention. TB...Cuttle, WK...Workpiece, PDC...Pulse distributor, MZ...Z-axis feed motor, SM...
Spindle motor, PC...Pulse coder, VD...Speed detection section, ZMV...Z-axis movement speed calculation section, PCC...
...Position correction calculation section, GT...Gate.

Claims (1)

[Claims] 1. A pulse distribution calculation is executed in synchronization with a sampling pulse of a constant period ΔT after the generation of a one-rotation signal that is generated every time the spindle motor makes one rotation, and the cutter is moved relative to the workpiece in the Z-axis direction. In a turning control device that performs turning processing on a workpiece while moving the workpiece,
By changing the generation timing of the sampling pulse, n・ΔT is generated after the one rotation signal is generated.
(n is an integer). When the turning speed in the Z-axis direction is Fz and the delay time of the servo system is Td, Fz・(n・ΔT+Td), a position correction means that controls the movement of the cutter relative to the workpiece in advance, and a pulse distribution calculation is executed in synchronization with the sampling pulse that is generated when n・ΔT has elapsed since the generation of the one-rotation signal. 1. A turning control device comprising: movement control means for controlling movement of a cutter relative to a workpiece.