Cutting apparatus with a cutting tool that, depending on the total length of the cutting line, is pressed with a varying pressure against a series of sequential workpieces

Abstract: A cutting apparatus presses a wheel cutter (12) against a ceramic plate (15) for cutting it along a cutting line, and a controlling unit (14b) determines the total cutting length so as to increase the pressure against the ceramic plate (15) together with the total cutting length, thereby keeping the depth of cutting trail constant.

Description: FIELD OF THE INVENTION This invention relates to a cutting apparatus and, more particularly, to a cutting apparatus equipped with a cutting tool variably pressed against a brittle workpiece of ceramic or glass depending upon running hours. DESCRIPTION OF THE RELATED ART A typical example of the cutting apparatus for a glass plate and a ceramic plate is called a "scriber", and figure 1 illustrates the scriber available for cutting a ceramic plate. The prior art scriber largely comprises a working table structure 1, a wheel cutter 2, a driving system 3 for the wheel cutter 2 and a controlling system 4 for the driving system 3. The working table structure 1 includes a rigid base 1a, a movable table 1b movable in Y-direction with respect to the rigid base 1a and a driving mechanism (not shown) for moving the movable table 1b under the control of the controlling system 4. A workpiece or a ceramic plate 5 is mounted on the movable table 1b, and is moved together with the movable table 1b in the Y-direction. The wheel cutter 2 is supported by a suitable retainer 2a, and the retainer 2a is functionally connected to the driving system 3. The driving system 3 includes a slide 3a and a servo-motor (not shown), and moves the retainer 2a and, accordingly, the wheel cutter 2 in X-direction with respect to the rigid base 1a. As shown in figure 2, the controlling system 4 includes a pusher 4a provided for the retainer 2a and a pneumatic control sub-system 4b. A cylinder 4c, a plunger 4d movable in the cylinder 4c and a return spring 4e form in combination the pusher, and the retainer 2a is connected to the leading end of the plunger 4d. The plunger 4d is reciprocally movable and moves telescopically from and into the cylinder 4c. The pneumatic control sub-system 4b is connected to a high-pressure air source 4f, and includes a combination unit 4g of air filter and pressure regulator, a lubricator 4h and a solenoid-operated three-port valve 4i. The three ports are labeled with "P", "A" and "R", and the solenoid 4j and a return spring 4k change the connection between the three ports "P", "A" and "R". The high-pressure air is supplied to the inlet port "P", and the outlet port "A" is connected to the cylinder 4C. The port "R" is open through a silencer 4m to the air. When no current is supplied to the solenoid 4j, the return spring 4k connects the outlet port "A" to the port "R", and the solenoid-operated three-port control valve 4i discharges the high-pressure air from the cylinder 4c through the silencer 4m to the air. The plunger 4d retracts into the cylinder 4c, and the retainer 2a and, accordingly, wheel cutter 2 are spaced from the ceramic plate 5. On the other hand, when a controller (not shown) energizes the solenoid 4j, the electro-magnetic force changes the connection from 'port "A" to port "R"' to 'port "P" to port "A'". Then, the high-pressure air is supplied to the cylinder 4c, and the plunger 4d extends from the cylinder 4c. The wheel cutter 2 is pressed against the ceramic plate 5. The pneumatic sub-system 4b further includes a manually-operated pressure reducer 4n for regulating the high pressure air to an appropriate value and a pressure switch 4o for monitoring the air pressure. When an operator manipulates the pressure reducer 4n, the manually-operated pressure reducer 4n regulates the high-pressure air to a new value, and the pressure against the ceramic plate 5 is changed depending upon the regulated air pressure. When,the air pressure is unintentionally decreased below a critical value due to, for example, air source failure, the pressure switch 4o supplies an alarm signal to the controller (not shown), and the controller informs an operator of an emergency state. The prior art scriber thus arranged encounters a problem in that the cutting performance is deteriorated with running hours of the wheel cutter 2. The reason for the deterioration is derived from the abrasion of the wheel cutter 2. In detail, while the wheel cutter 2 is cutting a ceramic plate, the cutting line or trail of the wheel cutter 2 is getting shallower and shallower with increase of the total cutting length as shown in figure 3. The high pressure air in the cylinder 4c is constant at P1, and the depth of the cutting line is proportional to the pressure against the ceramic plate. The pressure against the ceramic plate and, accordingly, the depth of the cutting line are decreased with increasing running hours or the total length cut by the wheel cutter 2 as indicated by Plots PL1. Thus, the depth of the cutting line is decreased, and the cutting performance is deteriorated. Of course, if the wheel cutter 2 is replaced with a new wheel cutter upon reaching the limit P3 of the allowable range dP, the cutting performance is good. However, the running hours of the wheel cutter 2 is short, and, accordingly, the frequent replacement increases the running cost of the prior art cutting apparatus. In order to improve the cutting performance without sacrifice of the running cost, an operator may step-wise increase the air pressure from P1 to P0 as indicated by Plots PL2 in figure 4. The depth of the cutting line is repeatedly adjusted within the allowable range dP as indicated by plots PL3, and the service time of the wheel cutter 2 is prolonged to L2. However, the operator is expected to periodically check the depth of the cutting line and exactly regulate the air pressure. This monitoring work is not easy, and the operator sometimes forgets the check. This results in deterioration of the cutting performance. Another prior art cutting apparatus is equipped with a pneumatic control sub-system 14 shown in figure 5. The pneumatic control sub-system 14 has three paths 14a, 14b and 14c arranged in parallel between the pressure switch 40 and the solenoid-operated three-port control valve 4i. However, the other components are similar to the prior art pneumatic control sub-system 4b shown in figure 2. The three paths 14a, 14b and 14c have respective pressure reducers 14d, 14e and 14f and respective solenoid-operated two-port control valves 14g, 14h and 14i, and the pressure reducers 14d, 14e and 14f are regulated to different values between P1 and P0. The solenoid-operated two-port control valves 14g, 14h and 14i are electrically connected to the controller (not shown), and one of the solenoid-operated two-port control valves 14g, 14h and 14i couples the associated pressure reducer to the solenoid-operated three-port control valve 4i. The controller selectively energizes the solenoids of the two-port control valves 14g, 14h and 14i, and increases the air pressure supplied to the solenoid-operated three-port control valve 4i. Then, the depth of the cutting line traces plots PL3 without the manipulation of the pressure regulator by an operator. However, the pneumatic control sub-system 14 is complicated, and the installation cost is high. Moreover, the pressure reducers 14d, 14e and 14f are the manually-operated type, and the operator is expected to exactly set the pressure reducers 14d, 14e and 14f to appropriate values. The manual regulation is necessary for different ceramic plates, and the operator sometimes forgets it. SUMMARY OF THE INVENTION It is therefore an important object of the present invention to provide a cutting apparatus which is simple and low in running/installation costs. To accomplish the object, the present invention proposes to automatically vary the pressure of the cutting tool against a workpiece depending upon the total length of the cutting line of such a tool. In accordance with the present invention, there is provided a cutting apparatus for cutting a series of workpieces as set forth in claim 1. Preferred embodiments of the invention may be gathered from the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS The features and advantages of the cutting apparatus according to the present invention will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which: Fig. 1 is a front view showing the prior art scriber; Fig. 2 is a block diagram showing the pneumatic sub-system incorporated in the prior art scriber; Fig. 3 is a graph showing the depth of the cutting line in terms of the total length of said cutting line without regulation of the air pressure; Fig. 4 is a graph showing the depth of the cutting line in terms of the total length of said cutting line under the regulation of the air pressure; Fig. 5 is a block diagram showing the pneumatic control sub-system incorporated in the other prior art scriber; Fig. 6 is a block diagram showing a cutting apparatus according to the present invention; Fig. 7 is a block diagram showing a pneumatic control sub-system incorporated in the cutting apparatus; Fig. 8 is a flow chart showing a control sequence for the cutting apparatus; and Fig. 9 is a graph showing the depth of a cutting line in terms of the total length of said cutting line under the control of a controlling system incorporated in the cutting apparatus. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to figure 6 of the drawings, a cutting apparatus embodying the present invention largely comprises a working table structure 11, a wheel cutter 12, a driving system 13 for the wheel cutter 2 and a controlling system 14. The working table structure 11 includes a stationary rigid bed 11a, a movable table 11b movable in a direction D1 with respect to the stationary rigid bed 11a and a driving mechanism 11c for moving the stationary rigid bed 11b. An electric motor, a reduction gear unit and a pinion/rack may form in combination the driving mechanism 11c. The direction D1 is perpendicular to the paper where figure 6 is illustrated and to directions D2 and D3. The wheel cutter 12 is supported by a retainer 12a, and is freely driven for rotation around an axis (not shown). The wheel cutter 12 is a sintered product of artificial diamond powder. The retainer 12a and, accordingly, the wheel cutter 12 are associated with the driving system 13, and are moved in the directions D2 and D3. The driving system 13 includes a servo-motor unit 13a, a stationary frame work 13b and a rotation-to-liner motion converting mechanism 13c. The stationary frame work 13b is provided over the working table structure 11, and is constituted by bracket members 13d and 13e and two guide rods 13f and 13g. The bracket members 13d and 13e are spaced apart from each other by a distance not shorter than the length of the movable table 11b, and the guide rods 13f and 13g extend in parallel between the bracket members 13d and 13e. A ball thread unit serves as the rotation-to-linear motion converting mechanism 13c. Namely, a male screw rod 13h, a female screw block 13i and balls (not shown) form the ball thread unit, and the male screw rod 13h is assembled with the female screw block 13i in in-phase manner. Though not shown in the drawings, the balls are inserted into the spiral gap between the male screw rod 13h and the female screw block 13i, and are circulated in the spiral gap. The male screw rod 13h is rotatably supported by the two bracket members 13d and 13e, and is connected to the shaft of the servo-motor unit 13a by means of a suitable coupling unit 13j. A movable bracket 13k is fixed to the female screw block 13i, and is slidable on the guide rods 13f and 13g in the direction D2. While the servo-motor unit 13a is rotating the male screw rod 13h in one direction, the movable bracket 13k slides on the guide rods 13f and 13g toward the bracket 13d and vice versa. The driving system 13 further includes an electric motor unit 13m and a rotation-to-linear motion converting unit 13n provided between the electric motor unit 13m and a cylinder 14t supported by the movable bracket 13k. The rotation-to-linear motion converting unit 13n is similar to the rotation-to-linear motion converting unit 13h/13i, and no further description is incorporated hereinbelow for avoiding repetition. While the electric motor unit 13m is rotating, the cylinder 14t is moved in the direction D3, and presses the cutter 12 against, or spaces it from a workpiece on the movable table 11b. The controlling system 14 includes a pneumatic control sub-system 14a and a controlling unit 14b, and the controlling unit 14b directly controls the driving mechanism 11c, the rotation-to-linear motion converting mechanism and the pneumatic control sub-system 14a through a data processing. Namely, though not shown in the drawings, a data processor, a program storage, a data storage and an signal interface are incorporated in the controlling unit 45b, and the data process executes instructions supplied from the program storage as will be described in detail in conjunction with a cutting operation on the ceramic plate 15. The pneumatic control sub-system includes a high pressure air source section 14c, a pre-treatment and adjusting section 14d, a controlling section 14e and an actuator section 14f. An air compressor unit 14g and a reservoir tank 14h form in combination the high pressure air source section 14c, and supplies high-pressure air to the pretreatment and adjusting section 14d. When the air pressure in the reservoir tank 14h reaches an upper limit, the air compressor unit 14g interrupts the air compressing. However, if the air pressure in the reservoir tank 14h is lowered to a lower limit, a pressure switch 14h' detects the low pressure, and instructs the air compressor unit 14g to restart the operation. Thus, the high-pressure air source section 14c supplies the high-pressure air between the higher limit and the lower limit to the pre-treatment and adjusting section 14d. The pretreatment and adjusting section 14d contains an air filter 14i, an air pressure regulator 14j and a separator 14k. The air filter 14i eliminates dust from the high-pressure air, and the air pressure regulator 14j keeps the air pressure constant. The separator 14k supplies lubricant such as lube oil into the high-pressure air for the actuator 14f and valves of the controlling section 14e. The controlling section 14e contains a pressure switch unit 14m, a voltage-to-air pressure converting valve unit 14n and a solenoid-operated three-port control valve unit 14o. The pressure switch unit 14m monitors the high-pressure air supplied from the pretreatment and adjusting unit 14d, and generates an alarm signal AL indicative of an actual air pressure lower than a critical level. The alarm signal AL is supplied to the controlling unit 14b. The voltage-to-air pressure converting valve unit 14n is responsive to a potential or voltage signal VT indicative of a target value of the high-pressure air so as to regulate the actual air pressure to the target value. A solenoid 14p is incorporated in the voltage-to-air pressure converting valve unit 14n, and generates electro-magnetic force in the presence of the potential signal VT. The electro-magnetic force is variable with the voltage level of the potential signal VT, and changes a throttle (not shown) for changing the air pressure at the outlet port thereof. The throttle is further controlled in such a manner as to keep the air pressure to the target value regardless of the amount of air flow. The potential signal VT is step-wise variable, and, accordingly, the voltage-to-air pressure converting valve unit 14n can step-wise vary the actual air pressure. In an actual control, the step of the potential variation is so narrow that the voltage-to-air pressure converting valve unit increases the air pressure as if it traces a linear line. The solenoid-operated three-port control valve unit 14o has an inlet port P, an outlet port A and discharge port R. The inlet port R is connected to the outlet port of the voltage-to-air pressure converting valve unit 14n, and the outlet port A is connected to the actuator 14f. The discharge port R is open through a silencer 14q to the air. The solenoid-operated three-port control valve unit 14o is bi-stable. Namely, a return spring 14r causes the outlet port A to be connected to the discharge port R in the absence of a change-over control signal CH supplied form the controlling unit 14b. However, when the change-over control signal CH is supplied to a solenoid 14s, the inlet port P is connected to the outlet port A, and the high-pressure air is transferred from the voltage-to-air pressure converting valve unit 14n to the actuator 14f. The cylinder 14t, a plunger 14u and a return spring 14v constitute the actuator 14f. The outlet port A is connected to the cylinder 14t, and supplies the high-pressure air to the inner chamber of the cylinder 14t. The plunger 14u is slidably accommodated in the inner chamber of the cylinder 14t, and the retainer 12a is connected to the leading end of the plunger 14u. The plunger 14u is urged into the cylinder 14t by the return spring 14v, and moves telescopically from and into the inner chamber depending upon the pressure in the inner chamber of the cylinder 14t. The retainer 12a is moved together with the plunger 14u in the direction D3, and the wheel cutter is pressed against, on spaced from a ceramic plate 15 mounted on the movable table 11b. In this instance, the wheel cutter 12 supported by the retainer 12a serves as a tool, and the actuator 14t behaves as the pressing means. The servo-motor 13a, the stationary frame structure 13b, the rotation-to-linear motion converting unit 13c and the coupling unit 13j as a whole constitute a driving means. The high-pressure source section 14c, the pre-treatment and adjusting section 14d and the controlling section 14e form in combination a controlling means, and a measuring means is implemented by the controlling unit 14b as will be understood hereinbelow. Assuming now an operator fixes the ceramic plate 15 to the movable table 11b, the driving mechanism 11c aligns the wheel cutter 12 with an imaginary cutting line on the ceramic plate 15. The controlling unit 14b instructs the servo-motor unit 13a to move the bracket 13k to a starting point above the right end of the ceramic plate 15. Although the air compressor unit 14g has stored the high-pressure air in the reservoir tank 14h, the controlling unit 14b does not supply the change-over control signal CH to the solenoid 14s, and the solenoid-operated three-port control valve unit 140 conducts the atmospheric pressure to the inner chamber of the cylinder 14f. For this reason, the return spring 14v causes the plunger 14u to retract into the inner chamber, and the wheel cutter 12 is spaced from the ceramic plate. When the operator instructs the controlling unit 14b to start the cutting operation on the ceramic plate 15, the controlling unit 14b minimizes the potential level of the potential signal VT, and instructs the voltage-to-air pressure converting valve unit 14n to regulate the actual air pressure to the minimum target value. Subsequently, the controlling unit 14b supplies the change-over control signal CH to the solenoid 14s, and the solenoid-operated three-port control valve unit 140 connects the inlet port P to the outlet port A as shown in figure 7. Then, the high-pressure air is supplied through the solenoid-operated three-port control valve unit 14o to the inner chamber of the cylinder 14t. The plunger 14u extends or projects from the cylinder 14t, and presses the wheel cutter 12 against the right end of the cutting line on the ceramic plate 15 at the minimum pressure. The controlling unit 14b instructs the the servo-motor unit 13a to rotate the male screw rod 13h. The rotation-to-linear motion converting unit 13c moves the movable bracket 13k and, accordingly, the actuator 14f and the wheel cutter 12 along the cutting line toward the left end of the ceramic plate 15. The wheel cutter 12 cuts the ceramic plate along the cutting line, and a trail or cutting line of the wheel cutter 12 is left in the ceramic plate 15. When the wheel cutter 12 reaches the left end on the cutting line, the controlling unit 14b instructs the servo-motor unit 13a to stop the rotation, and the movable bracket 13k and the wheel cutter 12 terminate at the left end on the cutting line. The controlling unit 14b removes the change-over control signal CH from the solenoid 14s. Then, the wheel cutter 12 stops the rotation, and the return spring 14r causes the outlet port A to be connected to the discharge port R. Then, the high-pressure air is discharged from the inner chamber of the cylinder 14t through the solenoid-operated three-port control valve unit 14o and the silencer 14q to the atmosphere. The return spring 14v causes the plunger 14u to retract into the cylinder, and the wheel cutter 12 is spaced from the ceramic plate 15. Thus, the cutting apparatus repeats the cutting operation on ceramic plates 15. When the wheel cutter 12 is replaced with a new one, the data processor resets an internal register of the data storage to, zero. While the wheel cutter 12 is cutting along the cutting line, the data processor increments the total length of the cutting line, and checks the total length of the cutting line to determine the potential level of the voltage signal VT. In detail, the data processor executes a main routine program, and controls the driving mechanism 11c, the driving system 13 and the controlling system 14 for cutting or scribing the ceramic plate 15. In order to control the controlling system, the data processor repeats a routine shown in figure 8 during the cutting operation. First, the data processor fetches the data indicative of the total length of the cutting line stored in the internal register as by step SP1, and compares the total length of the cutting line with a table defining relation between the total length and the target value of the high-pressure air. The table is established in the data storage. The table divides the length of the cutting line into narrow ranges, and associates the narrow ranges with different target values, respectively. However, the target value is varied as if it traces a linear line as described hereinbefore. The data processor determines the target value through the comparison with the table as by step SP2, and instructs a signal generator to regulate the voltage signal VT to the potential level indicative of the target value as by step SP3. The data processor allows the signal generator to supply the voltage signal VT to the voltage-to-air pressure converting valve unit 14n as by step SP4, and increments the total length of the cutting line as by step SP5. Thus, the data processing unit reiterates the loop consisting of steps SP1 to SP5 until the service life of the wheel cutter 12 is expired. The total length of the cutting line is measured as follows. If a numerical control is employed, the data processing unit calculates the total length on the basis of the control data for the numerical control. If the cutting line is constant, the data processing unit multiplies the length of the cutting line by the number of repetition so as to determine the total length of the cutting line. A revolution meter such as an encoder plate is fixed to the shaft supporting the wheel cutter 12, and the number of the rotations is reported to the data processing unit. The data processing unit multiplies the circumference of the wheel cutter by the number of rotations so as to determine the total length of the cutting line. Thus, the controlling unit 14b updates the total length of the cutting line, and varies the target value of the high-pressure air. As a result, the pressure against the ceramic plate 15 is increased together with the total length of the cutting line as indicated by plots PL4, and the depth of the cutting line is maintained constant as indicated by plots PL5 (see figure 9). This results in a constant cutting performance, and prolongs the life of the wheel cutter 12. Moreover, the controlling unit 14b changes the target value for the high-pressure air, and the wheel cutter 12 is exactly controlled without an error. While the cutting apparatus is carrying out the cutting operation on the ceramic plate 15, the high-pressure air is assumed to become lower than the critical value, the pressure switch 14m produces the alarm signal AL, and supplies the alarm signal AL to the signal interface of the controlling unit 45b. The controlling unit acknowledges the emergency state, and removes the change-over control signal CH from the solenoid 14s. Then, the solenoid-operated three-port control valve 14o connects the outlet port A to the discharge port R, and the high-pressure air is evacuated from the inner chamber of the cylinder 14t to the atmosphere. As a result, the return spring 14v causes the plunger 14u to retract into the cylinder 14t, and the wheel cutter 12 is spaced from the ceramic plate 15. The controlling unit 45b further instructs the servo-motor 13a to stop the rotation, and generate an alarm sign on a display (not shown). Although particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the scope of the present invention as defined in the claims. For example, an electric circuit and a solenoid-operated actuator may be used instead of the pneumatic control sub-system 14a and the actuator 14f. Moreover, the driving mechanism may rotate the movable table so as to carry out a position control in rotational coordinates. The wheel cutter may be replaced with a scriber, and may be rotated by a motor unit.

Claims: A cutting apparatus for cutting a series of workpieces (15) supported by a stationary structure (11a/13b), comprising: a cutting tool (12) supported by said stationary structure (11a/13b) and relatively movable with respect to each of said workpieces (15) in sequence; a pressing means (14f) for pressing said cutting tool (12) against each of said series of workpieces (15); and a driving means (13a/13b/13c) for providing relative movement between said cutting tool (12) and each sequential one of said series of workpieces for producing cutting lines in said series of workpieces (15), characterized by comprising a measuring means (14b) for measuring the total length of said cutting lines in said series of workpieces (15); and a controlling means (14b/14c/14d/14e) for adjusting the pressure with which said cutting tool is pressed against said series of workpieces (15) in accordance with said total length of said cutting lines, thereby making the dimensions of said cutting lines constant. The cutting apparatus as set forth in claim 1, in which said cutting tool is a wheel cutter (12). The cutting apparatus as set forth in claim 1, in which said pressing means (14f) includes a cylinder (14t) having an air chamber therein, a plunger (14u) projectable from and retractable into the cylinder (14t) and a return spring (14v) urging said plunger (14u) in a direction to retract into said cylinder (14t). The cutting apparatus as set forth in claim 3, in which said driving means includes a motor unit (13a), a stationary frame structure (13b) provided over said workpiece (15), a movable bracket (13k) supporting said cylinder (14t) and linearly movable with respect to said stationary frame structure (13b), and a rotation-to-linear motion converting unit (13c) connected between said motor (13a) and said movable bracket (13k) for reciprocatingly moving said movable bracket (13k). The cutting apparatus as set forth in claim 3, in which said controlling means includes a high-pressure air source (14c) for generating high pressure air, a pre-treatment and adjusting section (14d) for producing available high-pressure air from said high-pressure air, a controlling unit (14b) producing a voltage signal (VT) indicative of a target value for the high-pressure air variable with said total length of said cutting lines, and a pneumatic controlling valve section (14e) having a voltage-to-air pressure converting valve unit (14n) responsive to said voltage signal (VT) for regulating said available high-pressure air to said target value and supplying said available high-pressure air regulated by said voltage-to-air pressure converting valve unit to said cylinder (14t).

Inventors: TAKEDA KOSHIRO, TAKEDA, KOSHIRO, Takeda, Koshiro, c/o Yamaha Corporation
Applicants: YAMAHA CORP, YAMAHA CORPORATION
Application year: 1995
Main classification: C03B33
IPC codes: C03B33, B28D7, B28D1, B26D1