JPS641267B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention detects abnormal conditions such as the risk of tool damage or breakage during cutting using rotating tools such as drills and taps, and reduces the tool life. The present invention relates to a breakage prevention device for a rotary tool that can be used for determining, replacing a tool, or performing an appropriate tool protection operation to prevent tool breakage.

It is well known that a torque limiter is used as a breakage prevention device for rotating tools to prevent breakage. The same situation led to the destruction of the torque limiter, which caused the problem that it could not be applied to automatic machining.

As a breakage prevention device for rotating tools that can be applied to automatic machining, there is a method of predicting breakage using changes in the load current of the electric motor that drives the tool, and a method that predicts breakage using a strain gauge attached to the tool holder or machine spindle. A method for detecting ratios and predicting tool breakage based on these changes, as well as acoustic emissions that naturally occur as a result of tool damage or breakage.
For example, the elastic vibrations generated during the operation of a torque limiter are detected externally to predict tool damage or breakage. However, in all of these methods that do not use a torque limiter, the detection signal is related to the magnitude of the cutting torque applied to the tool.
(mm or less), the cutting torque is small, so the detection signal is also small, which reduces reliability and makes it difficult to apply to automatic driving.

There are two types of methods using torque limiters: a contact type that detects the elastic vibrations generated when the torque limiter operates directly from the tool holder, and a non-contact type that detects by installing a detector at a position away from the tool holder. . However, with the former, there are difficulties in transmitting elastic vibrations between the rotating and non-rotating parts of the tool holder, and special measures are required for the signal transmission means, and with the latter, the S/N ratio of the signal is poor. However, there were problems such as a lack of certainty.

The present invention has been developed in view of the current situation, and when the torque limiter assembled to the tool holder operates, it stably generates a large level detection signal regardless of the magnitude of the cutting torque applied to the tool, and is capable of producing a high-level detection signal for small-diameter tools. The purpose of the present invention is to provide a breakage prevention device for rotating tools that can also be applied to automatic operation.

That is, the breakage prevention device of the present invention includes a tool holder main body that is attached to a machine main shaft and rotated;
a tool gripping shaft rotatably fitted to the tool holder body; a transmission member that transmits the rotational force of the tool holder body to the tool gripping shaft; a torque limiter assembled to the transmission member; an attached piezoelectric body; a pressurizing means for pressurizing the piezoelectric body to generate a high voltage in conjunction with relative movement between the tool holder body and the transmission member that occurs when the torque limiter operates; A discharge terminal conducts high voltage and generates an electromagnetic wave, and the electromagnetic wave from the discharge terminal is received as a detection signal by an antenna, amplified, detected, and converted into a pulse signal, and the pulse signal is generated when the torque limiter operates. and a detection unit that confirms that the device is a device.

According to the present invention, the piezoelectric body is pressurized in conjunction with the relative movement between the tool holder body and the transmission member that occurs when the torque limiter operates, and the high voltage generated in the machined piezoelectric body is discharged to generate electromagnetic waves. Since this electromagnetic wave is used as a detection signal, a constant signal can be obtained regardless of the magnitude of the cutting torque applied to the tool. Therefore, it can also be applied to prevent damage and breakage of small diameter tools. In particular, the detection unit converts the electromagnetic wave into a pulse signal, and determines whether the number of occurrences of the pulse signal within a certain period of time matches the number of occurrences of the pulse signal determined from the spindle rotation speed and the structure of the torque limiter; Reliability will be extremely high if the configuration is such that nozzles and detection signals from electric motors, electromagnetic switches, high-frequency generators, welders, and other devices inside the factory are reliably distinguished.

In addition, since the electromagnetic wave that is the detection signal can be detected outside the tool holder in a non-contact state, it is only necessary to assemble the piezoelectric body, the pressure means for the piezoelectric body, and the discharge terminal into the tool holder body. The device is simple, lightweight, and easy to handle.

Embodiments of the present invention will be described below based on the drawings. Reference numeral 1 denotes a tool holder body, which includes a cylindrical part 2 for holding a rotary tool such as a drill or tap, a taper shank part 3 and a collar part 4 integrally connected to the rear end.
The tapered shank portion 3 is fitted into the tapered hole 7 of the main shaft 6 of the machine tool to be attached.
A drive key 8 protruding from the main shaft 6 is engaged with a keyway 5 provided in the collar 4 and rotates together with the main shaft 6.
9 indicates a mechanical fixing part.

Reference numeral 10 denotes a transmission cylindrical shaft, which is fitted into the cylindrical portion 2 of the tool holder main body 1 via a key 11, and an adjustment nut 13 is screwed into a threaded portion 12 carved on the outer periphery of the front portion of the transmission cylindrical shaft. The structure allows the protrusion length to be adjusted.

Reference numeral 14 denotes a tool gripping shaft, which is rotatably fitted to the transmission cylinder shaft 10, and in the illustrated embodiment, a tap 15 is used as a rotary tool, and its floating mechanism 1
6 is incorporated, it is also possible to slide in the axial direction within a certain range. Rotary tool (tap)
15 is fitted onto and held at the tip of the tool gripping shaft 14. Further, the latter half of the tool gripping shaft 14 is formed into a hollow shaft, and a square hole 18 is provided in the rear wall portion 17 in order to engage a transmission member to be described later.

Reference numeral 20 designates a transmission member, which consists of a main body disc 21, a square shaft 22 protruding from one side thereof, and a screw shaft 23 protruding from the opposite side.
The screw shaft 23 is slidably engaged with the screw shaft 23, and a torque limiter to be described later is assembled to the screw shaft 23. Also, disk 2
Clutch grooves 24 for the torque limiter are provided at three locations on the third side surface, and an annular mounting groove 25 is formed on the outer periphery (see FIG. 3). The above transmission member 2
0 is rotatably fitted to the transmission cylinder shaft 10 by fitting the disc 21 to the rear end of the transmission cylinder shaft 10 via a steel ball 26 that engages with the annular groove 25.

The torque limiter 30 includes a steel ball 31 that engages with each clutch groove 24, a retainer 32 that is rotatably fitted onto the screw shaft 23 and holds the steel balls 31, and a retainer 32 that is fitted into the retainer 32 and is pressed against the steel balls 31. a back ring 33 that is mounted on the screw shaft 23, a disc spring 34 that is fitted onto the screw shaft 23 and presses the steel ball 31 into the clutch groove 24 via the back ring 33, and a torque that is screwed onto the screw shaft 23 and adjusts the spring pressure of the disc spring 34. It is composed of a setting nut 35. As clearly shown in FIG. 4, a pair of protrusions 36, 3 are provided on the front end surface of the retainer 32 to face each other in the diametrical direction.
6 is a notch 3 formed at the rear end of the transmission cylinder shaft 10
7 and 37, rotational force is transmitted from the transmission cylinder shaft 10 to the retainer 32, and further transmitted from the retainer 32 to the tool gripping shaft 14 via the steel balls 31, the disk 21, and the square shaft 22.

A piezoelectric body 40 is attached to the rear end of the cylindrical portion 2 of the tool holder body 1 from the side, as shown in FIGS. 1 and 2. 41 is a piezoelectric body 40
The hammer is attached to the tip of a leaf spring 42 that is attached to the inner side of the cylindrical portion 2 via a mounting piece 43 in a cantilever structure. Reference numeral 44 denotes cam protrusions that engage with the leaf spring 42, and are set at equal intervals on the outer circumference of the rear end of the torque setting nut 35, and are engaged with the leaf spring 42 at regular intervals when the torque limiter 30 is operated. Together, they have the effect of repelling the leaf spring 42. 45 and 46 are discharge terminals, one discharge terminal 45 is connected to the positive side of the piezoelectric body 40,
The other discharge terminal 46 is connected to the negative side of the piezoelectric body 40 via the tool holder body 1, and is disposed inside the cylindrical portion 2 so as to face each other. Reference numeral 47 denotes a through hole through which an electromagnetic wave as a detection signal generated between the discharge terminals 45 and 46 is emitted to the outside, into which an insulating sleeve 48 is fitted. 49 is a through hole 47
An antenna that receives electromagnetic waves emitted through
It is installed on a mounting base 9' attached to the machine fixing part 9.

Next, the operation of the above device will be explained. First, the torque setting nut 35 is adjusted so that the torque limiter 30 is activated when the torque applied to the rotary tool 15 during cutting exceeds a certain threshold value (life torque 5).

Therefore, if the cutting edge of the rotary tool 15 wears out during cutting and approaches the end of its life, or if it becomes clogged with chips and the cutting torque increases significantly, there is a risk that the tool 15 will be damaged or broken. The torque limiter 30 operates, and a slip occurs between the transmission member 20 and the retainer 32 and therefore the transmission cylinder shaft 10, and the rotary tool 15, tool gripping shaft 14, transmission member 20, torque setting nut 35 and the cam protrusion are caused to slip. 44 stops. On the other hand, since the tool holder main body 1 continues to rotate, the leaf spring 42 rotates around the cam projection 44 which is in a stopped state, and this relative movement causes the leaf spring 42 to rotate intermittently with the cam projection 44. The hammer 41 attached to the plate spring 42 applies pressure to the piezoelectric body 40 due to the elastic force that is engaged and repelled.
High voltage occurs intermittently. The high voltage thus generated in the piezoelectric body 40 causes a spark discharge or corona discharge between the discharge terminals 45 and 46 to generate electromagnetic waves. The electromagnetic wave is received by the antenna 49 through the through hole 47 as a detection signal.

The electromagnetic waves received by the antenna 49 are sent to the detection section 100 shown in FIG. Next, when a voltage larger than a preset threshold is detected in the amplitude discriminator 53, an oscillation command is given to the pulse oscillator 54. Note that if the voltage is smaller than the threshold value, it is determined that the torque limiter 30 is not operating and that the tool 15 is performing normal cutting.

However, as mentioned above, since electromagnetic waves are used to transmit the signals from the discharge terminals 45 and 46 to the antenna 49 without contact, a lot of noise is mixed into the factory during the above transmission process. This is an obstacle to reliably detecting only the signal when the torque limiter 30 is activated. Therefore, an angle detector 101 is provided which outputs a signal when the main shaft 6 reaches a certain angular position.
between the two signals emitted from the main axis 6
A counter 102 counts the number of pulses sent from the pulse generator 54 during one rotation of the pulse generator 54 . This count number is input to the comparator 103, and it is compared whether this count number matches the number of times the hammer 41 hits the piezoelectric body 40 (the number of hits) during one rotation of the main shaft 6. The number of strikes is preset by the structure of the torque limiter 30.

If the count number matches the number of strikes, it is determined that the torque limiter 30 has been activated, and the alarm signal generator 104 issues an abnormality alarm and sends it to the controller to prevent the tool 15 from breaking. A protective operation to prevent this is performed according to a preset command procedure. If the two do not match, it is determined that the torque limiter 30 is not operating, and processing and monitoring continue.

When the above protective operation is repeated many times and the predetermined criteria are exceeded, the tool 15 has reached the end of its life due to wear etc., but the cutting conditions are inappropriate (for example, the workpiece is too hard. , excessive feed, etc.), an alarm is issued, and appropriate measures are taken, such as stopping the machine and replacing the tool.

In the detection section shown in FIG. 5, an angle detector 101 is used, but instead of the angle detector,
The controller of the NC machine tool outputs the spindle rotation speed, calculates the time required for one rotation of the spindle 6 from this output, generates a signal at this time interval, and generates a signal sent from the pulse oscillator 54 within this time interval. The counter 102 may count the number of pulses that come.

In addition, if the nozzle is not in bad condition, it is also possible to determine whether the torque limiter 30 is operating by determining whether the time intervals of the pulse signals sent from the pulse oscillator 54 are constant. can. That is, the generation times ti, ti _-1 , ti _-2 , . . . of each pulse signal are measured, and the time interval Δti=ti−ti ₋₁ between each pulse signal is calculated. Furthermore, the difference in time interval (△ti), i.e. △ti ~ △ti _-1
Calculate. △ti〜△ti _-1 obtained in this way
is a substantially constant value regardless of the magnitude of the set torque at which the torque limiter 30 operates, so this is used as a reference for comparison with noise. For example, △ti〜△ti _-1
If the condition of ≦0.1△ti _-1 is satisfied, it can be considered that the pulse signal is generated regularly, and therefore it is determined that the torque limiter 30 is operating. On the other hand, if △ti〜△ti _-1 >0.1△ti _-1 ,
The pulse signal is irregular and this is caused by torque limiter 3.
0 is not activated, but is determined to be a pulse signal due to noise.

As described above, the device of the present invention can detect these abnormalities when an overload is applied to the rotating tool during machining work and there is a risk that the tool will break, or when the tool life is nearing the end due to wear of the cutting edge. Since the condition can be reliably detected regardless of the magnitude of the set torque value of the torque limiter, it is particularly effective for in-process detection of abnormal conditions of small-diameter tools with low cutting torque.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional front view showing an embodiment of the breakage prevention device for a rotary tool according to the present invention, Fig. 2 is a sectional view taken along line 2-2' in Fig. 1, and Fig. 3 is a perspective view of the transmission member. 4 are perspective views of the retainer and the rear end portion of the transmission cylinder shaft, and FIG. 5 is a system diagram of the detection section. 1... Tool holder body, 2... Cylindrical part, 10...
...Transmission tube shaft, 14...Tool gripping shaft, 20...Transmission member, 30...Torque limiter, 40...Piezoelectric body, 41... Hammer, 42...Plate spring, 44...Cam protrusion, 45, 46... ...Discharge terminal, 47...Through hole, 49...Antenna.

Claims (1)

[Scope of Claims] 1. A tool holder main body that is attached to a machine main shaft and rotated, a tool gripping shaft that is rotatably fitted to the tool holder main body, and a rotational force of the tool holder main body that is applied to the tool gripping shaft. a transmission member that transmits the torque, a torque limiter assembled to the transmission member, a piezoelectric body attached to the tool holder body, and a transmission member that is linked to the relative movement between the tool holder body and the transmission member that occurs when the torque limiter operates. a pressurizing means that pressurizes the piezoelectric body to generate a high voltage; a discharge terminal that guides the high voltage of the piezoelectric body and generates an electromagnetic wave; and an antenna that receives the electromagnetic wave from the discharge terminal as a detection signal and amplifies it. A device for preventing breakage of a rotary tool, comprising: a detecting section that detects and converts the pulse signal into a pulse signal, and confirms that the pulse signal is generated during operation of a torque limiter. 2. The pressurizing means includes a leaf spring attached to the tool holder main body in a cantilevered structure, a hammer attached to the leaf spring, and a hammer attached to the transmission member, and the pressurizing means is attached to the tool holder main body when the torque limiter is operated. and a cam that intermittently engages with the leaf spring in conjunction with the relative movement of the transmission member and acts to repel the leaf spring, and the hammer of the repelled leaf spring causes the piezoelectric body to be activated. The breakage prevention device for a rotary tool according to claim 1, which is configured to apply pressure.