JPH02131839A - Automatic control method for vibration cutting device - Google Patents

Abstract

PURPOSE:To enable an eligible control with good accuracy by detecting the mechanical vibration of a tool under vibration cutting as frequency quantity and controlling cutting conditions based on this vibration frequency in a vibration cutting device cutting a tool by its vibration. CONSTITUTION:When a tool holder 3 is fitted into a main shaft 1 and a throttle valve 45 is opened, compressed air is fed into the gap 13 between a tool adaptor 10 and sliding member 11 through an air passage 56 by an air feeding path 43. The main shaft 1 is then rotated and while a normal working is performed by the tool of the adaptor 10, the ball 20, 28 of a torque limit mechanism 18 and thrust limit mechanism 19 are fitted into recessed place 21, 26, the adaptor 10 and a sleeve 8 are rotated together and the adaptor 10 is slightly vibrated in the fore and aft directions. This vibration is increased, reversely transmitted to the adaptor 10 and vibration cutting is executed. Meanwhile, the pressure fluctuation inside and passage 56 is caught as frequency in a pressure sensor 47, compared with a reference frequency and based on this comparison value the number of main shaft rotation and cutting feed amt. are controlled.

Description

Detailed Description of the Invention (Industrial Field of Application) This invention provides a vibration cutting device that performs cutting by applying vibration to a tool, which detects the cutting state during cutting and adjusts the rotational speed according to the cutting state. Or, it relates to an automatic control method that appropriately changes feed conditions. [Prior art] Conventionally, applying appropriate vibration to a tool during cutting can improve chip disposal, improve machining accuracy, or improve tool performance. It is known that vibration cutting has excellent effects such as improved durability.In order to obtain these effects of vibration cutting, the applicant has already developed a method that effectively utilizes the automatic vibration of the tool that occurs during cutting. A patent application was filed in 1983 for a vibration cutting device that performs vibration cutting.
This has been proposed in No. 2-80021 and Japanese Patent Application No. 135658/1983. These vibration cutting devices have a vibrating member with a tool mounting section attached to a tool holder attached to the main shaft of a machine tool so that it can move in the cutting direction, and an elastic force is imparted to this vibrating member to return it to its normal position. Something,
The cutting vibration applied to the tool during cutting is increased by elastic force and transmitted back to the tool. [Problem to be solved by the invention] By the way, in recent years, unmanned operation of various machine tools has become extremely popular, and in parallel with this, effective measures have been taken to prevent variations in the lifespan and damage of cutting tools of machine tools. is strongly requested. For this reason, various automatic control methods and devices have been proposed that constantly detect the cutting force during cutting and immediately adjust the rotational speed or cutting feed rate when excessive or insufficient cutting force is detected. However, the cutting force detection means used in conventional automatic control equipment is to attach detectors such as resistance wire strain gauges, differential transformers, and capacitance detectors to the spindle or cutting feed table. There is a problem that this detector cannot be used at all with the vibration cutting equipment mentioned above. In other words, in vibration cutting, in which machining is performed by applying vibration to the tool, for example, if the cutting force is measured using a resistance wire strain meter, the obtained value only indicates the amount of vibration, and has no meaning; vibration can damage the detection mechanism of resistance wire strain meters, etc. Therefore, in vibration cutting equipment, a new detection method different from the conventional detection method is required to detect the cutting force during cutting. This invention is above! This is a solution to III, and provides an automatic control method that accurately detects the cutting rod state of the tool during vibration cutting and corrects the cutting conditions according to the cutting state. [Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention detects the mechanical vibration of a tool that occurs during cutting as a frequency quantity, and compares the detected vibration frequency with a reference frequency. However, a method was adopted in which the spindle rotation speed or cutting feed amount was changed based on this comparison value. If damage occurs to the tool during cutting, an acoustic emission signal (hereinafter referred to as A) generated from the tool or machine tool
It is known that the output level of the descendant frequency component of the E signal is high. In addition, conventionally, AE during cutting
There is a tool damage prevention device that detects a signal and stops the movement of the machine tool when a high frequency component with a high output level appears in the signal. The present inventors believe that the above-mentioned relationship between the vibration frequency of the AE signal and the cutting phenomenon also exists in the mechanical vibration of the tool and the cutting phenomenon, and the inventors believe that the above-mentioned relationship between the vibration frequency of the AE signal and the cutting phenomenon also exists in the mechanical vibration of the tool and the cutting phenomenon, and detects this mechanical vibration as a frequency quantity. The cutting conditions were then controlled based on this detected frequency. In addition, the mechanical vibration of the tool is determined by providing an air passage on the surface of the tool with the outlet facing each other, converting it into pressure fluctuation within this air passage, and detecting this pressure fluctuation to determine the vibration frequency. Good too. By determining the vibration frequency in a non-contact state with a vibrating tool in this way, it is possible to always obtain a stable frequency regardless of the tool's movement or shape, compared to methods that use piezoelectric elements to detect it in a contact state. can. (Function) If the frequency of the mechanical vibration of the tool is detected and the change in the detected frequency is displayed over time from the start of cutting, the relationship shown in Figure 4 (a) is obtained.
The figure shows that the frequency increases significantly in the initial stage of cutting, but after the initial stage, the frequency remains uniform. When contact occurs or there is an excess or deficiency in the depth of cut (1+time), the frequency temporarily increases, and when the above condition disappears, the frequency returns to the steady frequency. Also, the frequency is
As the wear of the cutting edge of the tool progresses, the frequency f gradually increases or decreases, and when chipping or chipping occurs on the cutting edge of the tool, as at time t2, the frequency f shows a rapid increase. In the above phenomenon, the increase in frequency at the initial stage of cutting is considered to be a transient process in which the rotational speed or feed rate is in an acceleration mode until it stabilizes. Therefore, when performing control, except for the initial stage of cutting, it is necessary to start from the point when the frequency is in a steady state. Furthermore, since cutting is in a normal state in a steady state after the initial stage has passed, it is desirable to set the frequency in this state as the reference frequency.

The above operations can be omitted from the control range by, for example, using a timer to prevent detection of the initial stage of cutting. Furthermore, the reference frequency is obtained by sampling a plurality of frequencies within a reference time (several seconds) from the start of detection, calculating the average of these, and setting the average value as the reference frequency rc. The control is performed by comparing the reference frequency fc and the frequency f obtained during actual cutting, and outputs a control signal to the control device of the machine tool based on this comparison value. That is, the ratio f between the reference frequency fc and the frequency 1 at the time of measurement
/f c is taken, and when this ratio f / f c exceeds or falls below a certain control width a from 1, a control signal is sent to the control device of the machine tool to change the spindle rotation speed or cutting feed rate. Furthermore, the control in the above case is performed by dividing the control contents depending on the magnitude of the frequency ratio f/fc and the temporal change in the value. That is, as shown in FIG. 4(b),
When the frequency ratio r/fc increases and the change occurs within a certain time range, the spindle rotation speed or cutting feed amount is decreased according to the amount of change in the frequency ratio f/re, and the vibration frequency is reduced. When the frequency ratio f/fC falls inside the control radius a, the spindle rotation speed or cutting feed rate is returned to the set value. On the other hand, if the frequency ratio r/fc changes sharply and occurs within a short period of time, it is determined that a chipping of the cutting edge has occurred, and the spindle rotation and cutting feed are immediately stopped. Furthermore, if the change in the frequency ratio f/fc exceeds a predetermined value due to a gradual change over time, it is determined that the wear of the cutting blade has reached a certain value, and a signal to replace the cutting blade is issued. [Example] Figures 1 to 3 show a tool rotation type vibration cutting device. In FIG. 1, 1 is the main shaft of a machine tool such as a machining center, 2 is a fixed part of the machine body, and the main shaft 1 is driven by an appropriate driving means. The tool holder 3 consists of a rotating member 4 and a non-rotating member 5 that supports the rotating member 4. A tapered shank 6 that fits into the tapered hole of the main shaft 1 is provided at the rear of the rotating member 4. There is. A grip 7 is formed at the front of the taper shank 6 and engages with a claw of an ATC manipulator, and a rotating sleeve 8 is attached to the tip of the grip 7 via a screw 9. A tool adapter 10 having a tool attachment portion 10a and a sliding member 11 are attached to the inner hole 8a of the sleeve 8 so as to be airtight and movable in the front-rear direction. A slight gap 13 is provided between the tool adapter 10 and the sliding member 11 by making a ball 12 provided at the front of the sliding member 11 come into contact with the rear surface of the tool adapter 10. A coil spring 14 is installed between the sliding member 11 and a partition wall provided halfway inside the sleeve 8 to bias the sliding member 11 and the tool adapter 10 toward the front. Further, a support part 17 for the non-rotating member 5 is attached to the outer periphery of the sleeve 8 via front and rear bearings 15 and 16, and a torque for connecting the sleeve 8 and the tool adapter 10 is applied to the front and rear of the support part 17, respectively. A limit mechanism 18 and a thrust limit mechanism 19 that connects the sleeve 8 and the sliding member 11 are provided. The torque limit mechanism 18 includes a ball 20, a recess 21 formed on the outer periphery of the tool adapter 10 to receive the ball, a spring 22 and a spring receiver 23 that press the ball 20 into the recess 21, The spring receiver 23 is crimped onto the inner peripheral surface of a torque adjuster nut 24 attached to the front end of the sleeve 8. As shown in FIG. 2, the inner circumferential surface of the adjuster nut 24 is formed symmetrically so that it gradually becomes deeper from one end so that it becomes part of a spiral at a position 180" out of phase. 24 as shown by the arrow in the figure, the spring 22 is gradually compressed, the force applied to the ball 20 against the recess 21 becomes stronger, and the torque transmitted between the sleeve 8 and the adapter 10 increases.

The structure of the thrust limit machine side 19 is basically the same as the torque limit mechanism 18 described above, and a spring 27 and a ball are connected between the inner peripheral surface of the thrust adjusting star nut 25 and the recess 26 on the outer periphery of the sliding member 11. 28 and a spring support interposed therebetween, and an inclined surface for adjustment similar to that shown in FIG. 2 is formed on the inner circumferential surface of the star nut 25. Further, an annular member 29 is fixed to the inner periphery of the non-rotating member 5, and the inner surface of the annular member 29 is connected to the communication hole 30 of the sleeve 8.
It is in airtight contact with the outer circumferential surface at the location where it is provided. The through hole 30 communicates with a circumferential groove 31 formed on the outer circumference of the tool adapter 10 , and this circumferential groove 31 communicates with the gap 13 between the tool adapter 10 and the sliding member 11 through a communication passage 32 . There is. Furthermore, a radial communication hole 33 communicating with the communication hole 30 is provided inside the annular member 29. A fluid receiving portion 34 is integrally provided on one side of the non-rotating member 5, and a retaining pin 35 is attached to a vertical hole passing through the fluid receiving portion 34 vertically. On the other hand, the fixed part 2 of the machine tool is provided with an engagement hole 36 into which an engagement pin 35 is fitted.
A pressing member 37 is movably attached to the retaining pin in a state where the retaining pin is fitted into the engagement hole 36, and is pressed against the fixing portion 2 by the elasticity of the spring 38. The pressing member 37 is provided with an air introduction port 40 having a check valve 39, and this introduction port 40 communicates with a communication path 41 provided in the engagement pin 35. A communication passage 42 is provided for communicating the communication hole 33 of the annular member 29 with the communication hole 33 of the annular member 29. When the pressing member 37 is pressed against the fixed part 2, the check valve 39 is pressed open by a pin 39' protruding from the tip of the fixed part 2. On the other hand, in the fixed part 2 of the machine tool,
An air supply path 43 communicating with the air inlet 40 is provided, and this air supply path 43 includes a check valve 44 and a throttle valve 45.
A compressed air source 46 such as a compressor or receiver tank is connected via the. In the above structure, the compressed air source 4
The air coming out from the air supply path 43 is transferred to the air inlet 40 from the air supply path 43.
-1 passage 41-1 passage 42 → communication hole 33-4 communication hole 30 Complete passage 31 passage 32 will be introduced into gap 13, and from this air supply passage 43 to communication passage 32 is as follows. It is called the air passage 56. A pressure sensor 47 is provided at a branch path in the middle of the air supply path 43, and a control circuit 48 is connected to this pressure sensor 47. The pressure sensor 47 uses a pressure switch or the like, and when the pressure inside the air supply path 43 fluctuates, it switches and transmits an electric signal to the control circuit 48 every time the pressure fluctuates. FIG. 3 shows the structure of the control circuit 48, in which 49 is an amplifier, 50 is a hand-pass filter, and 5
1 is a timer, 52 and 53 are computing units, and 54 is a comparator, and this comparator 54 is connected to a control device M55 that controls the rotation of the main shaft of the machine tool and the feed of the tool rest. The operation of this control circuit 48 will be described later. Note that a circuit is configured for a throttle valve 45 provided between the air supply path 43 and the compressed air source 46 so as to maintain a desired pressure when the tool holder 3 is attached to the soil shaft 2. This embodiment has the structure described above, and its operation will be explained next. When the taper shank 6 of the tool holder 3 is fitted onto the raw shaft 1 and the throttle valve 45 is opened, compressed air is supplied from the air supply path 43 through the air path 56 to the gap 13 between the tool adapter 10 and the sliding member 11. Gap 1 like this
After compressed air is introduced into 3, the size of the gap 13 between the tool adapter 10 and the sliding member 11 is adjusted by turning the machine screw 12' via the ball 12. Next, when the main spindle 1 rotates and machining begins with the tool attached to the tool adapter 10, while machining is being performed normally, the torque limiter side 18 and thrust limiter f! 1B balls 20, 28 fit into the recesses 21, 28, respectively, and the tool adapter 10 and sleeve 8 rotate together.

In this case, since the tool adapter 10 and the sleeve 8 maintain a constant positional relationship, the circumferential groove 31 of the tool adapter 10
The positions of the communication hole 30 of the sleeve 8 and the sleeve 8 are aligned, and compressed air is retained at a predetermined pressure in the gap 13 and the air passage 56. When cutting is performed with the tool in this state, the engineer adapter 10 slightly vibrates in the front-rear direction due to cutting vibrations applied to the cutting edge of the tool. This vibration is amplified by the spring 22 of the torque limit mechanism 18 and transmitted back to the tool adapter 10, thereby performing vibration cutting. In this way, the tool adapter 10 during cutting
When the air passage 56 vibrates, the distance between the gaps 13 changes, and the pressure of the compressed air in the gaps 13 and the air passage 56 changes in accordance with this change. This pressure fluctuation is caused by a pressure sensor 4 installed in the air supply path 43.
7, the detection signal is converted into an electrical signal and captured as a frequency, and this detection signal is amplified by an amplifier 49 in a control circuit 48. The amplified frequency signal is then passed through a hand-pass filter 50, where frequency components other than those generated by cutting are removed. First, the initial part of cutting is removed from the frequency-separated output signal by the action of a timer 51. Next, when the steady machining state is reached, detection starts (to time). When detection is started, a plurality of frequency values are sampled at the first predetermined time and sent to the arithmetic unit 52. The arithmetic unit 52 calculates the average value of the sampled frequencies, determines the reference frequency fC, and outputs it to the next arithmetic unit 53. In this calculator 53, the reference frequency fc and the vibration frequency f continuously inputted from the hand-pass filter 50 are
is divided, and the ratio r/fc is obtained. In the next comparator 54, as shown in FIG. 5, the ratio f/fc obtained as described above is compared with the arbitrarily set control amount a, and the ratio f/fc If the ratio f/fc is exceeded, the temporal change in the change in the ratio f/fc is measured, and the control device 5 of the machine tool is controlled based on the measurement result.
A control signal is output to 5. This means that when the ratio f/fc deviates from the control amount a, the ratio Δf/Δt between the increase Δf of the ratio f/fc and the time amount Δt is calculated, and this ratio Δf/Δ
Three control techniques (sudden), (medium), and (slow) are selected based on the magnitude of [, and a control signal is output based on the selection. That is, in FIG. 4(a), when the frequency f increases within a certain rate due to excessive or insufficient depth of cut as shown in time [,, the (intermediate) control technique is selected and the ratio f /
A control signal is output that reduces the spindle rotation speed or cutting feed rate in accordance with the rate of increase in r c. This reduces cutting force and prevents tool breakage and abnormal cutting depth. Furthermore, when the cutting force decreases and the frequency ratio f/rc falls within the control amount a, the control signal is canceled and the spindle rotation and feed amount return to their original conditions. On the other hand, when a defect occurs in the workpiece as shown in time (.), the frequency r, that is, the frequency ratio f/fc, rises rapidly, so a (sudden) control technique is selected, and the spindle rotation and machine feed are immediately controlled. A control signal to stop is output.This causes
The machine tool will be stopped immediately. Furthermore, as shown by the broken line in Fig. 4(a), when the tool cutting edge wears out, the frequency f gradually increases, so when this is detected, the (gentle) control technique is selected and an alarm is issued to notify tool replacement. Or a signal is output to stop the machine tool. In addition to the causes mentioned above, this embodiment also has a structure in which the machine operation is stopped if the cutting resistance increases beyond a certain value due to causes such as poor tool selection or chip clogging. That is, when the cutting torque or thrust force increases beyond a certain level, the balls 20 and 28 come off from the recess 21 on the outer periphery of the tool adapter 10 and the recess 26 provided on the outer periphery of the sliding member 11, respectively, as shown in FIG. 10 no longer follows the rotation of the sleeve 80, and moves backward inside the sleeve 8, causing the positions of the circumferential groove 31 of the tool adapter 10 and the communication hole 30 of the sleeve 8 to shift. In this way, the communication hole 3
0 is cut off, the air pressure in the air passage 56 rises rapidly, the pressure sensor 47 senses this and the control circuit 48 amplifies it, and a signal to stop the machine operation is sent to the control device in the same way as in the case of a missing tool. 55. Fig. 6 shows another embodiment, in which it is applied to an outside diameter machining tool such as a lathe. In the figure, 57 is a tip holder with a tool tip 58 fixed to its tip;
The tip holder 57 is fastened at its rear end to the tip of the tool shank 61 via a leaf spring 59 and a washer 60. Further, an opening 62a is provided at the tip of the tool shank 61.
The air nozzle 62 faces the bottom surface of the chip holder 57.
An air passage 63 provided in the shank 61 communicates with this air nozzle 62, and an air supply passage 64 is connected to this air passage 63.
A compressed air source 46 is connected to the air supply path 64 as in the above embodiment, and a pressure sensor 47 is connected to the branch path.
A control circuit 48 is connected through the . In the vibration cutting device having the above structure, when cutting is started with air being blown out from the air nozzle 46, the tip holder 57 vibrates up and down due to cutting vibrations during processing, thereby performing vibration cutting. This vibration causes the air nozzle 6 to
The opening 62a of No. 2 also repeats opening and closing. As the lower surface of the chip holder 57 closes or opens the opening of the air nozzle 62, the air pressure within the air passage 63 fluctuates, and this pressure fluctuation is detected by the pressure sensor 47 and sent to the control circuit 48. Control in this control circuit 48 is performed in the same manner as in the embodiment described above. [Effects of the Invention] As described above, the present invention detects the mechanical vibration of a tool as a frequency quantity and controls the cutting conditions based on this vibration frequency. It is possible to accurately detect the cutting state of the tool being used, and to perform precise and accurate control. Furthermore, if the mechanical vibration of the tool is detected by converting it into pressure fluctuations in the air passage, the vibration of the tool can be detected without contact, so even if the shape of the tool changes, it can be detected in the same state. Unlike when using a contact-type vibration detector such as a piezoelectric element, this method does not have the drawback of deteriorating detection accuracy due to the durability of the detector, and has the advantage of always being able to provide accurate detection.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway diagram showing an example of a vibration cutting device embodying the present invention, Fig. 2 is a sectional view taken along line ■-n in Fig. 1, and Fig. 3 is a control circuit of the same. Fig. 4(a) is a block diagram showing the relationship between vibration frequency and time.
Figure (b) is a diagram showing the control state, Figure 5 is a diagram showing the relationship between frequency ratio and time, and Figure 6 is a diagram showing another embodiment of the vibration cutting device. 1... Main shaft, 3...
Tool holder, 8...Rotating sleeve, 10...
...Tool adapter, 11...Sliding member,
13...Gap, 18...Torque limit mechanism, 19...Thrust limit mechanism, 4
3... Air supply path, 46... Compressed air source, 47... Pressure sensor, 48... Control circuit, 55... Control Device, 56...
・Air passage, 57... Chip holder, 61... Tool shank, 62... Air nozzle, 63... Air passage, 64...・Air supply path. 1292-

Claims (2)

[Claims] (1) In a vibration cutting device that performs cutting while applying vibration to the tool, the mechanical vibration of the tool that occurs during cutting is detected as a frequency quantity, the detected vibration frequency is compared with a reference frequency, and this comparison is made. An automatic control method for a vibration cutting device, characterized by changing the spindle rotation speed or cutting feed amount based on a value. (2) The vibration cutting device according to claim (1), wherein mechanical vibration of the tool is converted into pressure fluctuation in an air passage provided in the tool, and a vibration frequency is obtained from the pressure fluctuation. Automatic control method.