JPH0112632B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a method for detecting contact between two objects having relative velocity, when at least one of the objects has electrically conductive properties, and in particular electrically detecting contact between a tool and a workpiece. Relating to a method for detecting. Conventionally, in order to detect contact between a tool of a machine tool and a workpiece with high sensitivity, it has been possible to detect electrical contact between the two only when both are made of conductive materials. However, in actual machining, either the tool or the workpiece is often made of a non-conductive material (insulator). In such cases, there was no suitable means for electrically detecting contact between the two. It is therefore an object of the invention to provide a means for enabling the detection of electrical contact between two objects having relative velocities and in contact with each other, even if one of the objects is non-conductive. The goal is to provide the following. In order to achieve the above object, the electrical contact detection method according to the present invention includes means for measuring a potential difference between the electrically conductive object of the two objects and the ground, and The gist of the present invention is to detect contact between the two objects based on a change in potential difference caused by an electromotive force generated when the two objects come into contact. When two bodies having relative velocities, one of which is stationary and the other rotating, the means for measuring the potential difference are determined by means of a contact formed by a rotating conductor in contact with a conductive liquid. Can be connected between two objects.
The invention is particularly advantageously applied when the two objects having the above-mentioned relative velocities are a tool and a workpiece. Hereinafter, the present invention will be explained in more detail using examples with reference to the accompanying drawings, but these are merely illustrative, and it is understood that various improvements and modifications may be made without going beyond the scope of the present invention. Of course. Here, we will discuss the electromotive force generated by contact. This electromotive force is considered to be a type of frictional electromotive force. When the grindstone and the workpiece come into contact, friction occurs between the two, and it is thought that this friction causes an electromotive force to be generated. Therefore, if the workpiece is suspended from the ground by an insulator, the potential difference between the workpiece and the ground can be measured. The electromotive force caused by this friction changes depending on the feed speed, etc., but since it is a binary determination of whether or not there is contact, there is no problem even if the electromotive force is small as long as it is amplified.
The problem is the humidity in the air, which neutralizes the frictional electromotive force, making detection difficult. However, air-conditioned rooms (clean rooms, etc.)
If the machine tool is placed inside the chamber and the humidity is kept below a predetermined value, the electromotive force can be detected satisfactorily for practical purposes. An example in which the present invention is applied to a grinding machine is shown in FIGS. 1 and 2. Normally, the main body of the grinding machine is grounded, so the table 4 is at ground potential as shown in FIG. There is.
Now, when the potential difference between the workpiece and the ground is measured by the contact detection/judgment circuit 5, an electromotive force is generated at the point of contact between the grindstone 1 and the workpiece 2 from the moment the rotary grindstone 1 comes into contact with the workpiece 2. Since a potential difference occurs between the workpiece and the ground, the contact detection and determination circuit 5 can detect the contact. The configuration of the contact detection and determination circuit 5 is shown in FIG. 1
3 is the measurement impedance (resistance, capacitance, etc.)
In the case of FIG. 1, this is connected between the workpiece 2 and ground. The potential difference between both ends of the measurement impedance 13 is amplified by an amplifier circuit 14, passes through a waveform shaping circuit (filter, rectifier circuit, etc.) 15, and is compared with a reference voltage _Vref in a comparator 16 to determine whether there is contact. In the example shown in FIG. 1 in which the present invention is applied to a grinding machine, the workpiece is supported by an insulating plate, so that rigidity and workability during grinding may become a problem. Figure 2 shows an improved version of this. In FIG. 2, the main shaft 7 is driven by a belt by a motor 8, and by grounding only the motor, the grinding machine frame 6 and the table 4 are suspended from the ground. The conductive workpiece 2 is fixed to a table 4, and the grinding wheel 1 is attached to the workpiece 2.
It is possible to detect the electromotive force when the workpiece comes in contact with the workpiece 2 or table 4 by a contact detection judgment circuit connected between the ground and the workpiece 2 or the table 4, as shown in Fig. 1. No loss of rigidity. The grinding wheel 1 of FIGS. 1 and 2 may be electrically conductive or non-conductive. Figures 3 and 4 show examples in which the present invention is applied to lathes.
As shown in the figure. The apparatus shown in FIG. 3 is of similar construction to that of FIG. That is, the main shaft 7 is belt-driven by the motor 8, and only the motor 8 is grounded, so the lathe framework 6, the main shaft 7, and the conductive workpiece 2 are floating from the ground. Part-time job 11 now
When the workpiece 2 contacts the rotating workpiece 2, an electromotive force is generated in the workpiece 2. Therefore, if the contact detection judgment circuit 5 is connected between the lathe framework 6 and the ground, 7. A current flows through the bearing and the lathe framework 6, and the contact can be detected. In the example shown in FIG. 3, since a current flows through the bearing, the detection accuracy of the determination circuit 5 may change slightly due to changes in the impedance (resistance value) of the bearing. FIG. 4 shows another embodiment for improving detection accuracy. In Fig. 4, the main shaft 7
An electrical contact 12 is provided at the end, and the potential difference between this electrical contact and ground is measured. Since the resistance value fluctuation at the electrical contact can be made very small, the detection accuracy of the contact detection and determination circuit 5 can be improved. In the case of FIG. 4, when the main shaft 7 driven by gears etc. rotates, electrical resistance is generated in the bearing, so even if the lathe frame 6 needs to be grounded, the conductive workpiece 2 The generated electromotive force causes a current to flow through the main shaft 7, the electrical contact 12, and the contact determination circuit 5, making it possible to detect contact. In FIG. 4, the cutting tool 11 is composed of a blade portion 9 and a shank 10, but the above-mentioned contact detection is possible whether the blade portion 9 is conductive or non-conductive. Furthermore, even if both the blade part 9 and the shank 10 are conductive, by insulating the entire cutting tool 11 from the ground,
Contact detection between the cutting tool 11 and the workpiece 2 can be similarly detected by connecting the contact detection and determination circuit 5 between the cutting tool 11 and the ground. In FIGS. 1 to 4 described above, by detecting the contact between the tool and the workpiece, it is possible to make a constant cut using the contact position as the origin and giving a constant depth of cut from there. It is an effective means for high-precision machining. Another example of the electrical contact 12 provided at the end of the main shaft in FIG. 4 is shown in FIG. 6. In the figure, a rod 17 is attached to the end of the main shaft 7 of the machine tool, a disk 18 is fixed to the tip of the rod 17, and the disk 18 is in contact with a conductive liquid 19 filled in a conductive contact case 20. Although it rotates together with the main shaft 7 in the soaked state, since it is always in contact with the liquid 19, electrical continuity is maintained between the main shaft 7 and the case 20. The contact detection/judgment circuit 5 shown in FIG. 4 is connected between the case 20 and the ground. Conventionally, the resistance value of the conductive liquid 19 was 0Ω.
For example, polluting substances such as mercury have been used to lower the temperature to near the surface, but this is not desirable from a safety standpoint because vaporized mercury comes out from the seal 21 and the like. For example, in order to transmit analog signals such as the output of a strain gauge mounted on the main shaft 7, etc., the only known fluid contact has been one that uses mercury because it is necessary to reduce the contact resistance value as much as possible. However, in the present invention, it is only necessary to electrically detect the two states of contact between the tool and the workpiece, and the resistance value of the liquid 19 may be large, so a non-polluting conductive liquid such as water may be used. When water is used, the electrical resistance can be maintained at, for example, 20 kΩ.
In this way, when the electrical resistance at the contact point is large, the measurement impedance 13 should also be made large (for example,
1MΩ) allows contact detection. For example, solder may be used as the liquid 19 in FIG. 6, and the solder may be liquefied while being heated by the heater 31. In Figures 2 and 3, it was stated that the machine tool frame is not grounded, but only the motor, which is a source of electrical noise, is grounded. There is a table feed motor that is difficult to install separately from the machine. Feed motors usually have a low wattage, so they are unlikely to be a source of electrical noise, but if noise becomes a problem, remove the motor from the machine tool frame or the feed mechanism (feed screw, gears, etc.) with an insulating material. It is sufficient to insulate and ground only the motor separately. FIG. 7 shows an example in which the present invention is applied to a vertical grinder. 24 is a tool such as a cutting tool, which is an example of polishing a certain amount of non-conductive material 22 such as diamond. In this case, the shank 23 is made of a conductive material,
The electromotive force generated when the shank 23 contacts the grindstone 1 is detected by the contact detection/judgment circuit 5, and the diamond 22 is ground until the shank comes into contact with the grindstone. Dimensional variations in the blade portion 22 can be relatively reduced. In FIG. 7, the shank 23 is insulated from the grinding machine frame 6 by an insulator 25 in order to float it from the ground. The grinding machine frame 6 may or may not be grounded, but if it is not grounded, the insulator 25 can be omitted. FIG. 8 shows an example in which the present invention is applied to a mold polishing machine. The grinding wheel 1 polishes the mold workpiece 2 while rotating, and a contact detection/judgment circuit 5 is connected between the workpiece 2, which is insulated from the ground, and the ground, and the contact detection/determination circuit 5 is connected between the grinding wheel 1 and the workpiece 2. Contact can be detected. Polishing machine body 2
6 is subjected to rough feed control in the X and Z directions, for example, by control units 27 and 28, respectively, based on a command input 34. A highly accurate feed control function can be added to this using the controller 29 so that the electromotive force at the time of contact between the grinding wheel and the workpiece is constant, and the workpiece 2 that has already been roughly machined can be turned into a highly accurate finished surface. It can be processed into 30 is a circuit that processes the signal of the contact detection determination circuit. In addition, instead of the electromotive force at the time of contact, a vibration sensor 32 is attached to the polishing machine, and the output of the vibration sensor is sent to the signal processing circuit 3.
It is also possible to perform feed control in which the control amount 33, which is the output, is inputted to 0 and kept constant. Here, an experimental example will be shown. A diamond whetstone was used as the whetstone. A diamond whetstone is made by solidifying diamond powder with a binder. Diamond powder is originally
It is an insulator. There are cases where a conductive resin is used as the binder, and cases where a non-conductive vitrified resin is used. The former is called a conductive whetstone,
The latter is called a non-conductive grindstone. Table 1 shows an example of the contact electromotive force between such a grindstone and a conductive workpiece. Examples of workpieces include titanium (Ti) and iron (JIS standard SS41).
An example is shown below. The experimental method involved connecting one end of a lead wire to the workpiece, and connecting a resistor R ₀ (=25KΩ) in series to the other end of the lead wire. The other resistor R ₀ had three modes. The first is an open state (Mode A), the second is a state where the room is grounded (Mode B), and the third is a state where it is directly connected to the table 4 (Mode C). Table 1 shows examples of potential differences across the resistor R ₀ under these three modes. here,
The detection potential difference of mode A is E(A), the mode B is E(B),
Mode C was designated as E(C). Also, the spindle rotation speed
4000rpm, bearing resistance 500Ω, workpiece pressing force 30~
It was set to 60gf.

[Table] According to the present invention, if either the tool or the workpiece is a conductor, it is possible to detect contact between the two, and by making constant cuts from the contact position or using a constant load machining method, finishing machining of high-precision machined products, etc. becomes possible. Further, the contact detection method of the present invention has the advantage of being simple in structure and low in cost.

[Brief explanation of drawings]

1 and 2 are schematic diagrams showing an example of applying the method according to the present invention to a grinding machine, and FIGS.
The figure is a schematic diagram showing an example in which the method according to the present invention is applied to a lathe, FIG. 5 is a block diagram of a contact detection judgment circuit that can be used to implement the method according to the present invention, and FIG. 7 is a schematic diagram showing an example of the application of the method according to the invention to the grinding of tools with a vertical grinder; FIG. FIG. 8 is a schematic diagram showing an example in which the method according to the present invention is applied to a mold polishing machine. DESCRIPTION OF SYMBOLS 1... Grinding wheel, 2... Workpiece, 3... Insulator, 4... Table, 5... Contact detection judgment circuit, 6... Machine tool frame, 7... Spindle, 8... Motor, 9... Bit part, 1
0...Shank, 11...Bite, 12...Contact, 13
...Measurement impedance, 14...Amplification circuit, 15
... Waveform shaping circuit (filter etc.), 16... Comparator, 17... Rod, 18... Disc, 19... Conductive liquid, 20... Contact case, 21... Seal, 22... Blade, 23... Shank, 24... Tools , 25... Insulator, 26... Mold polishing machine main body, 27... X-axis feed control section, 28... Z-axis feed control section, 29... Controller, 30... Vibration sensor, 31... Heater, 32... Vibration sensor, 33... Control amount, 34...command input.

Claims (1)

[Claims] 1. When at least one of two objects having a relative velocity has conductive properties, means for measuring the potential difference between the conductive object and the ground is provided,
An electrical contact detection method characterized in that contact between two objects having relative speeds is detected by a change in potential difference caused by an electromotive force generated when the two objects come into contact. 2. When two objects having relative velocities, one of which is stationary and the other rotating, the means for measuring the potential difference is determined through a contact formed by a rotating conductor in contact with a conductive liquid. 2. The electrical contact detection method according to claim 1, wherein said electrical contact detection method is connected between said conductive object and ground. 3. The electrical contact detection method according to claim 1, wherein the two objects having relative speeds are a tool and a workpiece.