JPH0525624B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spindle orientation method for a machine tool, and particularly to a method for stopping the spindle in the shortest possible time.

[Background technology]

A numerically controlled machine tool equipped with an automatic tool changer requires a function for stopping the spindle at a predetermined position (generally referred to as spindle orientation) in order to change tools.

By the way, the amount of inertia (GD ² ) differs depending on the material and size of the workpiece, but conventionally, deceleration control corresponding to this has not been performed, so the spindle stop time may become unintentionally prolonged. , reducing machining efficiency.

Hereinafter, conventional problems will be specifically explained using drawings.

FIG. 1 is a spindle speed/time graph showing an example of spindle orientation operation.

Generally, the spindle speed during spindle orientation operation ranges from machining speed N ₀ (usually around 400 to 6000 rpm) to orientation speed N ₃ (usually
200 rpm) at maximum deceleration, or accelerate from a standstill to orientation speed N ₃ at maximum acceleration, then creep speed N ₄ (usually
10rpm), and then the creep speed
It is rotated at _N4 (the above is the area where the speed is controlled), and then the position is controlled and it stops at a predetermined position.

For example, in a general magnetic sensor type orientation, a magnetic body is attached to a part of the main shaft, and the position of the main shaft is detected by detecting the magnetism with a fixed magnetic sensor. In Figure 1,
Point d is the point where magnetism is detected, and after one rotation, deceleration starts from point c, decelerates at a constant deceleration β, and reaches creep speed at point b. Point b is in the vicinity immediately before point a where the next magnetic field is detected. That is, the main shaft is decelerated toward the vicinity immediately in front of the magnetizing body.

However, since the size and material of the workpiece generally differ, if the amount of inertia GD ² of the workpiece is large, it may not be possible to decelerate the workpiece at the specified deceleration β using the deceleration capacity of the electric motor. In this case, the vehicle goes through a deceleration process as indicated by the broken line in FIG. 1, but the time it takes to reach point e from point f is very long because the speed N ₄ is very slow. On the other hand, if β is set to a low value assuming the maximum inertia of the workpiece GD ² , there is a drawback that the deceleration time from N ₃ to N ₄ will be extended when the workpiece GD ² is small. ing.

[Purpose of the invention]

The present invention has been made in order to eliminate the above-mentioned drawbacks, and is an optimum method for achieving a stop in the shortest time at a deceleration that does not exceed the maximum possible deceleration of the system determined by the inertia of the workpiece GD ² . The purpose is to determine the speed and perform deceleration control from the orientation speed to the creep speed.

[Specific description of the invention]

FIG. 2 shows a specific configuration example in which the present invention is applied to a thyristor Leonard type main shaft drive device.
In this figure, 1 is an AC power supply, 2 is a thyristor rectifier circuit, 3 is a rectifier circuit, 4 is a DC motor, 5 is a tacho generator, 6 is a DC current transformer, 7 is a phase shifter,
8 and 9 are amplifiers, 10 is a gear device, 11 is a main shaft, 12 is a magnetic generator, 13 is a magnetic sensor, 14 and 15 are changeover switches, 16 to 19 are comparators, 20
and 21 are R-S flip-flops, 22 and 2
3 is an AND circuit, 24 is an amplifier, 25 is a position command device, 26 is a D/A converter, and 27 is a speed command calculation circuit.

In FIG. 2, the thyristor 2 to the amplifier 9 constitute a known thyristor Leonard with a current minor loop. DC motor 4 and main shaft 11
are connected via a gear device 10. A magnetic body 12 is attached to the main shaft, and a magnetic sensor 13 is fixedly installed to detect the magnetism of this magnetic body. The aforementioned thyristor Leonard, magnetic sensor 13, amplifier 24, and position command unit 2
5 constitutes a position feedback control system with a speed minor loop. The main axis position detection characteristics of the magnetic sensor 13 are as shown in FIG. In FIG. 3, the range used as the position feedback control system is the characteristic between a and b.

The output of the magnetic sensor 13 is compared by a comparator 16, and as shown in FIG.
When the output of the magnetic sensor is larger than Vref, the output of the comparator 16 becomes 1, and when it is smaller, it becomes 0 signal.

The comparator 17 detects the polarity of the speed deviation voltage of the aforementioned thyristor Leonard. That is, when the speed detection value is smaller than the speed command value, the output of the comparator 17 is 1, and when it is larger, the output is 0.

The comparators 18 and 19 equivalently detect the speed of the main shaft 11 by detecting the speed of the DC motor 4, and their characteristics are shown in FIG.
If the spindle speed is N ₁ or more, the output of the comparator 18 is 1, and if it is N 1 or less, the output is 0. If the spindle speed is N ₂ or more, the output of the comparator 19 is 1, and if it is N 2 or less, the output is 0.

20 is an R-S flip-flop, and once the output of the AND circuit 22 becomes 1, its Q terminal stores the 1 state. When the output of the flip-flop 20 becomes 1, the changeover switch 15 is turned to the C side. 21 is also an R-S flip-flop, and when its output becomes 1, the selector switch 14 is switched to the A side.

27 is a speed command calculation circuit, comparator 18,
Based on the outputs of 19 and flip-flop 20,
This is a circuit that calculates speed commands.

The operation is as follows. At point g where cutting is completed in Figure 1, the speed command from the numerical control device is N ₀
The command speed Vs=Nos corresponding to _N3 changes in a stepwise manner to the speed command Vs= _N3S corresponding to N3.

In this case, the flip-flops 20, 2 in FIG.
Since the output of switch 1 is in the zero state, selector switch 1
4 and 15 are put into the B and D sides. Therefore, the main shaft 11 operates as a speed control system. However, since the vehicle is decelerating, the speed deviation is large and the output of the amplifier 9 is saturated. Therefore, the thyristor Leonard operates as a constant current circuit, and as a result, the DC motor 4 generates a constant deceleration torque,
The spindle speed decreases linearly from N ₀ to N ₃ as shown in FIG.

When the spindle speed reaches N ₁ and N ₂ , comparators 18 and 19 operate and generate an output signal of 1. The speed command calculation circuit 27 calculates the time from when the output of the comparator 18 becomes 1 to when the output of the comparator 19 becomes 1.
t〓 is measured, and the deceleration β ₀ at this time is determined from the first equation.

β ₀ = (N ₁ − N ₂ )/t〓 ...Equation 1 The speed command calculation circuit 27 has a digital configuration using a microcomputer, and the calculation of Equation 1 is performed until the spindle speed reaches N ₃ . Do this.

β ₀ in the first equation is the maximum deceleration determined from the capability of the thyristor Leonard in the current work.

Similarly, when the spindle speed accelerates from a stopped state to orientation speed N ₃ ,
The maximum deceleration is determined. That is, this is because the absolute values of deceleration and acceleration are equal.

Until the spindle speed reaches N ₃ , reduce the spindle speed to N
Then, N _3S <N, but after the main axis reaches N ₃ ,
N _3S >N, and the output of the comparator 17 becomes 1.
After that, when point c is reached, the output of the magnetic sensor 13 is at the reference level of the comparator 16, as shown in FIG.
Vref, comparator 16 produces an output of 1. Therefore, the output of the AND circuit 22 becomes 1, and the changeover switch 15 is switched to the C side. At the same time, the output of the flip-flop 20 becomes an input to the speed command calculation circuit 27. The speed command calculation circuit 27 generates an optimal deceleration command for decelerating from N ₃ to N ₄ , which becomes the speed command for the thyristor Leonard through the D/A converter 26 . The output terminal b of the speed command calculation circuit 27 generates a signal of 1 after point b in FIG.

The main shaft 11 reaches a creep speed N ₄ at point b.
After the magnetizing body 12 and the magnetic sensor 13 face each other at point c, the rotation angle θ ₀ o of the main shaft 11 up to point b is decelerated so that it satisfies the relationship expressed by the second equation, where n is an integer.

θ ₀ = n - Δθ ...Second equation In this second equation, the reason why the rotation angle at point b is smaller than n by Δθ is that even if there are variations in the speed control system, the first This is because at point a in the figure, a margin is provided so that the control enters between a and b in FIG. 3, and the shift from speed control to position control is ensured. In an ideal system with no variations, Δθ=0.

The present invention attempts to optimally control the deceleration from point c to point b in FIG.

Now, assuming that the elapsed time from point c is τ(s), the amount of rotation of the main shaft is θ (rev.), and the deceleration is β, the following equations 3 and 4 are obtained.

N=N ₃ −βτ ...Third equation θ=∫Ndτ, so θ=K(N ₃ -β/2τ)τ ...Fourth equation (K is a constant) Third and fourth equations By eliminating τ from , we get the following fifth
The formula is obtained.

N=√ ₃ ² − (2) ...Equation 5 Figure 4 shows the time change in speed when decelerating from spindle speed _N3 to creep speed _N4 . Even when decelerating at the deceleration β ₀ determined by Equation 1, A reaches the creep speed N ₄
At this point, the magnetizing body 12 and magnetic sensor 13 in FIG.
is not decelerating to the opposite position. Therefore, it is generally shown that at time A, there is a certain deviation angle between the magnetizing body 12 and the magnetic sensor 13. In other words, the deceleration β ₀ obtained by the first equation is the deceleration β _o at which the main shaft reaches the creep speed N ₄ in n rotations.
and the deceleration β _o-1 at which the main shaft reaches the creep speed N ₄ after n-1 rotations. This relationship is shown in FIG.

With the deceleration characteristic of β ₀ , the deceleration time t ₁ from N ₃ to N ₄ is expressed by Equation 6.

t ₁ = (N ₃ − N ₄ )/β ₀ ...Equation 6 Next, from the point when the creep rate reaches N ₄ , θ
The time t ₂ for rotating until = n - Δθ is expressed by the seventh equation.

t ₂ = {(n - Δθ) - 1/2 (N ₃ + N ₄ ) t ₁ } / N ₄ = (n - Δθ) - (N ₃ ² - N ₄ ² ) / 2β ₀ /N ₄ ...th Equation 7 Therefore, the sum of t ₁ and t ₂ is the time t _d required from the orientation speed N ₃ to stopping, and the 8th
Expressed by the formula.

t _d = t ₁ + t ₂ = N ₃ −N ₄ /β ₀ +{n−Δθ/N ₄ −N ₃ ² −N ₄ ² /2N ₄ β ₀
} = n - Δθ / N ₄ - (N ₃ - N ₄ ) ² /2N ₄ β ₀ ...Equation 8 From this Equation 8, the optimal deceleration with a small value (the shortest time deceleration that minimizes td) It can be seen that β _pp exists. In other words, as shown in Figures 4 and 5, even if the deceleration is at the maximum deceleration β ₀ , if it takes a lot of time to stop at the predetermined position (time to rotate at the creep speed N ₄ ), the maximum The time consumption t _d may be shorter if the vehicle is decelerated at a deceleration smaller than the deceleration β ₀ .

By the way, the relationship between the deceleration β _o and the rotation angle n−Δθ when t ₂ =0 is expressed by the ninth equation.

(N ₃ + N ₄ ) x (N ₃ - N ₄ )/2β _o = n - Δθ
... Equation 9 (∵(N ₃ - N ₄ )/β _o =t ₁ ) Therefore, from Equation 9, β _o is expressed as Equation 10.

βn = (N ₃ ² - N ₄ ² ) / 2 (n - Δθ) ...Equation 10 In other words, β _o that satisfies β _o ≦ β ₀ and is _the closest value to β ₀ is The optimal deceleration is β _pp . Also,
The commanded speed N _S with respect to time is expressed by Equation 11.

N _S =N ₃ -βop×t...Equation 11 A flowchart for determining the optimum deceleration βop and command speed N _S is shown in FIG. 6 and will be explained.

β ₀ is obtained by measuring N ₁ , N ₂ , and N〓, and β ₀ and β ₀ are sequentially compared from n=1, and the first β _o that satisfies β _o ≦β ₀ is set as βop.

Since β _o-1 is larger than the maximum deceleration, it is impossible to decelerate at that deceleration β _o-1 . This situation is shown in FIG.

N _S is commanded by the above-mentioned formula 11.

Note that this speed command value is at point c in FIG. 1, that is, the output of the comparator 16 becomes 1, and the
At the same time when the output of 0 becomes 1, the speed command calculation circuit 2
7 generates the value of equation 10 at the output terminal a. Since the selector switch 14 is switched to the C side by the output of the flip-flop 20, the main shaft 11 decelerates at a constant deceleration and reaches _N4 . At this time, the speed command calculation circuit 27 is generating the N _4S command, and the output terminal b generates a 1 signal.

Next, when the point a in FIG. 1 is reached, the magnetic sensor 13
Since the output of is at point c in Figure 3, the comparator 16 generates 1 signal, and at the same time the output of the comparator 17 is N _4S
>N ₄ , so it becomes one signal, and the AND circuit 22,
23 and the flip-flop 21 become 1, the selector switch 14 is switched to the A side, and the spindle 11 stops at the position commanded by the position command device 25. After the spindle 11 has stopped, a reset signal is given from the numerical control device, and the flip-flops 20 and 21 are reset.

Although this embodiment has been described using a thyristor Leonard as an example, it is of course applicable to an induction machine employing a vector control system. Further, the present invention can be easily applied to a digital position control method using a pulse generator or encoder other than a magnetic sensor for position detection.

〔Effect of the invention〕

As described above, in the present invention, when decelerating the machine tool spindle from the orientation speed to the creep speed, the process of decelerating from the machining speed to the orientation speed or accelerating from a stopped state to the orientation speed is performed in advance. _{In the process} ^of _{_} ^_ _{_ _ _} n is selected so that _it has the maximum value of The machine tool can also be stopped at a predetermined position in the shortest possible time, resulting in a significant increase in the machining efficiency of the machine tool.

[Brief explanation of the drawing]

FIG. 1 is a graph explaining an example of the operation of spindle orientation, FIG. 2 is a circuit diagram showing a specific configuration example of the present invention, FIG. 3 is a graph explaining the detection characteristics of a magnetic sensor, and FIGS. FIG. 5 is a graph explaining the shortest time stop, and FIG. 6 is a flowchart for determining the optimum deceleration and command speed. 1: AC power supply, 2: Thyristor rectifier circuit, 3:
Rectifier circuit, 4: DC motor, 5: Tacho generator, 6: DC current transformer, 7: Phase shifter, 8, 9: Amplifier, 10: Gear device, 11: Main shaft, 12: Magnetizing body, 13: Magnetic sensor, 14, 15: Changeover switch, 16 to 19: Comparator, 20, 21: R-S flip-flop, 22, 23: AND circuit, 2
4: Amplifier, 25: Position command device, 26: D/A converter, 27: Speed command calculator.

Claims (1)

[Scope of Claims] 1. When performing deceleration control from the orientation speed of the machine tool spindle to the creep speed, the process of decelerating from the machining speed to the orientation speed in advance or the process of accelerating from a stopped state to the orientation speed , the maximum acceleration/deceleration β ₀ is measured, and the acceleration/deceleration β _o expressed by the following formula is β _o ≦
Select n so that it has the maximum value that satisfies β ₀ , and set the optimum acceleration/deceleration _βop to the optimum acceleration/deceleration βop.
A spindle orientation method characterized by decelerating from orientation speed to creep speed. Formula β _o = (N ₃ ² − N ₄ ² )/2 (n − Δθ) (However, N ₃ is orientation speed, N ₄ is creep speed, and n is creep after starting deceleration from orientation speed. The number of revolutions required to reach the speed, Δθ is a small margin angle that takes into account errors and variations)