US3909989A

US3909989A - Grinding machine with feed rate changing device

Info

Publication number: US3909989A
Application number: US527858A
Authority: US
Inventors: Tamaki Tomita; Ryoji Yamada; Shiro Takayama
Original assignee: Toyoda Koki KK
Current assignee: Toyoda Koki KK
Priority date: 1974-03-09
Filing date: 1974-11-27
Publication date: 1975-10-07
Anticipated expiration: 1992-10-07
Also published as: FR2263072A1; JPS538397B2; JPS50120093A

Abstract

A grinding machine comprising: a bed; a wheel slide slidably mounted on said bed; a grinding wheel rotatably mounted on said wheel slide; a work table for supporting a workpiece; feed means for moving said wheel slide toward and away from said workpiece; an electric power source; a first electrode mounted adjacent to said grinding wheel and connected to said electric power source for applying a potential to the surface of said grinding wheel; a second electrode mounted adjacent to said grinding wheel for detecting the change of the difference of potential caused by the approach of said grinding wheel to a workpiece in order to generate a control signal; an electrostatic screening member for encircling said second electrode except at the surface thereof opposed to said grinding wheel, said electrostatic screening member being connected to the ground; and control means for controlling said feed means so as to change the feed rate of said wheel slide in accordance with said control signal.

Description

United States Patent Tomita et a1.

Oct. 7, 1975 GRINDING MACHINE WITH FEED RATE CHANGING DEVICE Inventors: Tamaki Tomita, Okazaki; Ryoji Yamada; Shiro Takayama, both of Kariya, all of Japan Toyoda Machine Works, LtdL,

Assignee:

Aichi-Pref., Japan Filed: Nov. 27, 1974 Appl. No.: 527,858

Foreign Application Priority Data Mar. 9,1974 Japan 49'27377 U.S. Cl 51/165.77; 5l/165.92 Int. Cl. B24B 49/08 Field of Search 51/165 R, 165.77, 165.87,

[56] References Cited UNITED STATES PATENTS 2,961,808 11/1960 Dungan 51/165.92 3,090,171 5/1963 Stimson 51/165 R 3,172,240 3/1965 Giardini..... 51/l65.92 X 3,550,327 12/1970 Kusakobe 51/l65.92

FOREIGN PATENTS OR APPLICATIONS 782,432 9/1957 United Kingdom 51/165.92

AMPLIFIER 1 OSCILLATOR REC T/F/ER ITE ME C/RCU/T CIRCUIT Primary Examiner-Harold D. Whitehead Attorney, Agent, or Firm-Oblon, Fisher, Spivak, McClelland & Maier [5 7] ABSTRACT A grinding machine comprising: a bed; a wheel slide slidably mounted on said bed; a grinding wheel rotatably mounted on said wheel slide; a work table for supporting a workpiece; feed means for moving said wheel slide toward and away from said workpiece; an electric power source; a first electrode mounted adjacent to said grinding wheel and connected to said electric power source for applying a potential to the surface of said grinding wheel; .a second electrode mounted adjacent to said grinding wheel for detecting the change of the difference of potential caused by the approach of said grinding wheel to a workpiece in order to generate a control signal; an electrostatic screening member for encircling said second electrode except at the surface thereof opposed to said grinding wheel, said electrostatic screening member being connected to the ground; and control means for controlling said feed means so as to change the feed rate of said wheel slide in accordance with said control signal.

4 Claims, 3 Drawing Figures GRINDING MACHINE WITH FEED RATE CHANGING DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to grinding apparatus, and more particularly to a grinding machine provided with an apparatus for changing the feed rate of a grinding wheel relative to a workpiece just before the grinding Wheel comes into contact with the workpiece.

2. Description of the Prior Art In recent years, there has been developed a grinding machine provided with a feed rate changing apparatus wherein the outer periphery of a nonconductive grinding wheel is sprayed with a conductive coolant so as to place it in a conductive state so that, when the grinding wheel comes into contact or approaches the workpiece, an electrical connection may be formed between the grinding wheel and the workpiece by the-conductive coolant. The feed rate changing apparatus is provided with a first electrode which is mounted adjacent to the grinding wheel for applying a potential to the surface of the grinding wheel and a second electrode adjacent to the grinding wheel for detecting the potential of the outer surface of the grinding wheel through an electrostatic induction phenomenon caused therebetween. Thus, the contact or approach of the grinding wheel with the workpiece is detected on the basis of the change of the detected potential.

It was, however. difficult for such a second electrode to accurately detect in a stable manner the change of potential because of an induced voltage caused by induction and radiation from the environment.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a grinding machine provided with a new and improved electrode device incorporated in an apparatus for changing the feed rate of a grinding wheel just before the grinding wheel contacts the workpiece.

It is another object of the present invention to provide a grinding machine provided with a new and improved electrode device having electrostatic screening for accurately detecting in a stable manner the approach of a grinding wheel to a workpiece.

Still another object of the present invention is to pro vide a grinding machine provided with a new and improved electrode device wherein a detecting electrode is screened by an electrostatic screening member so as not to be affected by electrostatic induction from the environment except at the surface of the grinding wheel opposed to the detecting electrode.

The foregoing and other objects are attained in accordance with one aspect of the present invention through the provision of a grinding machine which comprises a bed, a wheel slide slidably mounted on the bed, a grinding wheel rotatably mounted on the wheel slide. a work table for supporting a workpiece, a feed device for moving the wheel slide toward and away from the workpiece and other devices mentioned below. A first electrode is mounted adjacent to the grinding wheel and is connected to an electric power source for applying a potential to the surface of the grinding wheel. A second electrode is mounted adjacent to the grinding wheel for detecting the change of the difference of potential caused in the approach of the grinding wheel to a workpiece in order to generate a control signal. An electrostatic screening member connected to ground is mounted so as to encircle the second electrode except at the surfact thereof opposed to the grinding wheel. A control device controls the feed device so as to change the feed rate of the wheel slide in accordance with the control signal.

BRIEF DESCRIPTION OFTHE DRAWINGS The foregoing and other objects of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description of a preferred embodiment when considered in connection with the accompanying drawings, in which:

FIG. 1 is a schematic view showing apparatus for detecting the approach of a grinding wheel to a workpiece;

FIG. 2 is a longitudinal cross sectional view showing a second electrode device; and

FIG. 3 is a graph showing the relationship between the distance between a grinding wheel anda workpiece and output voltage.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to FIG. 1 thereof, there is shown a work table 2 which is slidably mounted on a bed 1. The work table 2 fixedly mounts a head stock 3 and a tail stock (not shown) for rotatably supporting a workpiece W therebetween. A wheel slide 4 is slidably mounted on the bed 1 so as to be moved twoard. and away from the supported workpiece W. The above-mentioned grinding machine parts are made of conductive material. A nonconductive grinding wheel G such as, for example, a bitrified grinding wheel is rotatably mounted on the wheel slide 4 through a wheel shaft 5.

A coolant nozzle 8 is secured on the top of a grinding wheel guard 12 for discharging coolant downwardly to the grinding point or contacting position of the grinding wheel G and the workpiece W during a grinding operation. A pump Pc is connected to the coolant nozzle 8 by means of a conduit 9 for supplying coolant from a coolant reservoir (not shown) to the coolant nozzle 8. A magnetic change-over valve is connected between the coolant nozzle 8 and the pump Pc for opening and closing the conduit 9. l

A feed cylinder 11 is mounted on the bed 1 for slidably receiving a piston and a piston rod 13 which is connected to the lower portion of the wheel slide 4. Fluid under pressure is applied to and is discharged from the cylinder 11 through a magnetic change-over valve 14 for changing the advance and the retraction of the wheel slide 4. Another change-over valve 15 is used for changing the feed rate of the wheel slide 4. A check valve 16 is connected between the cylinder 11 and the change-over valve 14 in parallel with the change-over valve 15 for permitting the wheel slide 4 to rapidly retract.

There will not be described a feed rate changing device which changes the feed rate of the wheel slide 4 or the grinding wheel G relative to the workpiece W just before the grinding wheel G contacts the workpiece W or when the grinding wheel G makes initial contact with the workpiece W.

A first conductive nozzle which serves also as a first electrode device to provide the electric potential of the periphery of the grinding wheel G is insulatedly fixed to the wheel slide 4 for supplying a conductive coolant to the periphery of the grinding wheel G in order to wet the grinding wheel G. The first conductive nozzle 20 is connected to the conduit 9 through a relatively long nonconductive pipe 21 to prevent the current applied thereto from leaking to the conductive coolant and in turn is connected to the pump Pc. A variable throttle 22 is interposed between the first conductive nozzle 20 and the conduit 9 for adjusting the quantity of coolant applied to the grinding wheel G so that an appropriate coolant film may be formed on the outer peripheral edge of the grinding wheel G.

A second nozzle 24 for the supply of the conductive coolant is insulatedly fixed to the side of the grinding wheel guard 12 and is opened adjacent to the clearance between the side of the grinding wheel G and a second electrode device 30. The second nozzle 24 is connected to the pump Pc through a relatively long nonconductive pipe 25 and a variable throttle 26 is interposed between the pump Pc and the second nozzle 24 for adjusting the quantity of coolant applied to the clearance between the side of the grinding wheel G and the second electrode device 30.

An air nozzle 27 is fixed to the rear side of the coolant nozzle 8 and the air-blowing opening thereof is opposed to the entire width of the outer peripheral edge of the grinding wheel G for discharging compressed air to prevent scatterring of the coolant.

The second electrode device 30 is mounted on the grinding wheel guard 12 and is adjacent to the side surface of the grinding wheel grinding as shown in FIG. 2. A body 31 made of an insulating material is fixed to the grinding wheel gaurd 12 so that the front end surface thereof 32 is opposed to the peripheral side surface of the grinding wheel G with a small clearance therebetween of, for example, 0.5 millimeters. A second electrode 33 of a metallic disk is fixed to the bottom of a round recession 31a which is formed on the body 31 with a distance or thickness of l millimeter from the 'front end surface of the body 31. An electrostatic screening member 34 made of a metallic material of cup shape is received in and fixed to a circular slot 31/; whih is formed on the body 31 so as to concentrically encircle the round recession 31a. Thus, the second electrode 33 is encircled by the electrostatic screening member 34 except at its face which is opposed to the side of the grinding wheel G. A shielding wire 36 is connected to the body 31 through a conventional connector 35. The shielding mesh conductor 36a of the shielding wire 36 is connected to ground at one end and is connected at the other end to the electrostatic screening member 34 and is insulated with respect to the second electrode 33. The second electrode 33 is connected to the central conductor 36b of the shielding wire 36. The central conductor 36/; is connected to a control circuit described hereinafter which controls the feed rate of the wheel slide 4 in accordance with the approach of the grinding wheel G to the workpiece W.

A high frequency oscillator 40 is provided as an electric power source to apply a potential to the surface of the grinding wheel G. In the present embodiment, the oscillator 40 is designed so as to transmit a high frequency voltage of 10 Kilohertz aand 30 volts from one output terminal thereof to the first conductive nozzle or first electrode 20. The other output terminal of oscillator 40 is connected to ground by bed 1.

There will now be described the control circuit which detects the potential of the peripheral surface of the grinding wheel G in order to control the changing operations of the magnetic change-over

valves

10, 14 and 15.

An amplifier 41 is connected to the second electride 33 through the central conductor 36b of the shielding wire 36 for amplifying the input voltage applied thereto. The output terminal of the amplifier 41 is connected to a high-pass filter circuit 42 which eliminates low frequency oscillations. In the present embodiment, the high pass filter circuit 42 is designed so as to permit carrier voltage oscillations to pass therethrough but to eliminate low frequency voltage fluctuations which are caused by drifts of electric circuit components and the fluctuation of commercial frequency (/60 Hertz). For example, if the frequency of the carrier current is 10 Kilohertz, the high-pass filter circuit 40 is designed to eliminate oscillations less than I Kilohertz.

A rectifier circuit 43 is connected to the output ter- I minal of the high-pass filter circuit 42 for rectifying and demodulating the carrier current transmitted there from. The output terminal of the rectifier circuit 43 is connected to a low-pass filter circuit 44 which is designed to eliminate oscillations of more than 10 Hertz such as pulsating voltage fluctuations which are not eliminated by the high-pass filter circuit 42 or the rectifier circuit 43.

The output terminal of the low-pass filter circuit 44 is connected to a memory circuit 45 which memorizes an input voltage just prior to the advance of the wheel slide 4 in accordance with a gate signal 45a which is transmitted by a retraction-confirming limit switch (not shown) when the wheel slide 4 is in its retracted position. The output terminal of the memory circuit 45 is connected to a voltage-reducing circuit 46 which reduces at a predetermined rate, for example /2, the output voltage of the memory circuit 45.

A comparator circuit 47 is connected at one input terminal to the output terminal of the low-pass filter circuit 44 and at the other input terminal to the output terminal of the voltage-reducing circuit 46. Thus, the comparator circuit 47 generates a feed rate changing signal when the output voltage of the low-pass filter circuit 44 is less than that of the voltage-reducing circuit 46. The output terminal of the comparator circuit 47 is connected to a relay circuit 48 which energizes the solenoides of the magnetic change-over

valves

10 and 15 when the feed rate changing signal is generated by the comparator circuit 47. j

The operation of the aforementioned preferred embodiment will now be described.

FIG. 1 shows the position prior to the grinding operation in which the wheel slide 4 and the other accompanying parts are in their initial positions or states. When an operation-starting signal is applied to the relay circuit 48, the pump Pc is driven to supply coolant to the first conductive nozzle 20 and the second nozzle 24. In addition, a pump P and an air pump (not shown) are driven to supply operational pressure fluid and compressed air, respectively. The coolant discharged from the first nozzle 20 and the second nozzle 24 is directed to the outer peripheral edge of the grinding wheel G and to the side surface of the grinding wheel G through the clearance between the grinding wheel G and the second electrode device 30.

The grinding wheel G starts to rotate in a counterclockwise direction in FIG. 1 in accordance with a start signal and is wetted by the coolant discharged from the first conductive nozzle 20. The variable throttle 22 is adjusted prior to the machining cycle so that the coolant is directed to the outer peripheral edge of the grinding wheel G without interruption and wets only the outer peripheral edge of the grinding wheel under the centrifugal force caused by the rotation of the grinding wheel G. The variable throttle 26 is adjusted so that the coolant supplied by the second nozzle 24 wets the side surface of the grinding wheel G radially outward beyond the electrode device 30 under the centrifugal force and does not wet in the vicinity of the wheel shaft 5 of the grinding wheel G. Thus, a conductive surface is formed by the conductive coolant on the outer peripheral edge and the outer peripheral side of the grinding wheel G which is maintained in nonconductive relationship with the wheel shaft 5.

The carrier oscillator 40 is then operated to transmit the carrier, for example, a kilokertz frequency at 30 volts. This voltage is applied to the periphery of the grinding wheel G through the coolant discharged from the nozzle so that a predetermined potential is given to the periphery of the grinding wheel G. A voltage which corresponds to the potential on the periphery of the grinding wheel G is caused by an electrostatic conduction phenomenon at the second electrode 33 and is directed to the input of the amplifier 41 through the shielding wire 36.

A relationship between the output voltage V of the low-pass filter circuit 44 and a distance S between the grinding wheel G and the workpiece W is shown in FIG. 3 wherein the output voltage V is V1 when the distance 5 is larger than a distance a and the output voltage V decreases because of the reduction of the potential on the periphery of the grinding wheel G as the grinding wheel G approaches the workpiece W within the distance a. The output voltage V attains V2 when the distance S is zero or when the grinding wheel G contacts the workpiece W.

Experimental data for the present invention was as follows when the distance a 0.3 millimeters Vl 2 volts and V2 0.7 volts When the wheel slide 4 starts to advance toward the workpiece W away from its retracted or initial position by the change-over of the valve 14 to the port (1) thereof, the gate signal 45a which is directed to the input of the memory circuit 45 is interrupted. The memory circuit 45 memorizes the voltage V2 just before the stoppage of the gate signal 45a and continues to transmit the voltage V2 until the wheel slide 4 returns to its retracted position. The voltage-reducing circuit 46 generates a reference voltage V0 which is reduced at a predetermined rate (for example, V0 V2/2).

' As the grinding wheel G approaches the workpiece W during the advance of the wheel slide 4, the output voltage V of the low pass filter circuit 44 decreases as shown in F IG. 3. When the output voltage V attains the reference voltage V0 of the voltage-reducing circuit 46 or when the distance S between the grinding wheel G and the workpiece W is equal to b, the feed rate changing signal is generated by the comparator circuit 47. The magnetic change-over valve 15 is changed to its port(l) in accordance with the feed rate changing signal to thereby change the feed rateof the wheel slide 4 from a rapid feed rate to a slow or grinding feed rate defined by a throttle contained in the valve 15. At the same time, the magnetic change-over valve 10 is changed to its. port (I) to thereby permit a large supply of coolant to be supplied from the coolant nozzle 8 to the grinding point. Thus, the grinding wheel G starts to grind the workpiece W.

In case the second electrode 33 is not provided with the electrostatic screening member 34, induced voltages due to radiation and induction of near electrical parts and transmission lines appear at the second electrode 33. For example, such an induction occurs in the changing operation of magnetic change-over valves or in the switching operation of contacts. An induced voltage having a frequency near the carrier frequency of the carrier ocillator 40 is not eliminated even by the high-pass filter circuit 42 and the low-pass filter circuit 44. The occurrence of such an. induced voltage disturbs the relationship between the output voltage V of the low-pass filter circuit 44 and the distance S between the grinding wheel G and the workpiece W. Therefore, the position where the feed rate of the wheel slide 4 is changed from the rapid to the slow is not maintained constant.

Since the second electrode device 33 according to the present invention is provided with the electrostatic screening member 34 encircling the second electrode 33, no induced voltage clue to radiation and induction of other electrical parts and transmission lines except the grinding wheel G occur with the result that the detected distance between the grinding wheel and the workpiece W is maintained stable.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is to be understood therefore that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. A grinding machine comprising:

a bed;

a wheel slide slidably mounted on said bed;

a grinding wheel rotatably mounted on side wheel slide;

a work table for supporting .a workpiece;

feed means for moving said wheel slide toward and away from said workpiece;

an electric power source;

a first electrode mounted adjacent to said grinding wheel and connected to said electric power source for applying a potential to the surface of said grinding wheel;

a second electrode mounted adjacent to said grinding wheel for detecting the change of the difference of potential caused by the approach of said grinding wheel to a workpiece in order to generate a control signal;

an electrostatic screening member for encircling said second electrode except at. the surface thereof opposed to said grinding wheel, said electrostatic screening member being connected to the ground; and

said first electrode is a conductive nozzle for supplying a conductive coolant to the periphery of said grinding wheel.

4. A grinding machine acording to claim 1 further comprising a coolant nozzle for supplying a conductive coolant to the clearance between said grinding wheel and said second electrode.

* l l= =l

Claims

1. A grinding machine comprising: a bed; a wheel slide slidably mounted on said bed; a grinding wheel rotatably mounted on side wheel slide; a work table for supporting a workpiece; feed means for moving said wheel slide toward and away from said workpiece; an electric power source; a first electrode mounted adjacent to said grinding wheel and connected to said electric power source for applying a potential to the surface of said grinding wheel; a second electrode mounted adjacent to said grinding wheel for detecting the change of the difference of potential caused by the approach of said grinding wheel to a workpiece in order to generate a control signal; an electrostatic screening member for encircling said second electrode except at the surface thereof opposed to said grinding wheel, said electrostatic screening member being connected to the ground; and control means for controlling said feed means so as to change the feed rate of said wheel slide in accordance with said control signal.

2. A grinding machine according to claim 1 further comprising a body made of an insulating material and having a circular slot for receiving said electrostatic screening member and a round recession encircled by said circular slot for receiving said second electrode.

3. A grinding machine according to claim 1 wherein said first electrode is a conductive nozzle for supplying a conductive coolant to the periphery of said grinding wheel.