CN108312371A - A kind of the closed speed control system and control method of wire sawing process - Google Patents
A kind of the closed speed control system and control method of wire sawing process Download PDFInfo
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- CN108312371A CN108312371A CN201810040787.2A CN201810040787A CN108312371A CN 108312371 A CN108312371 A CN 108312371A CN 201810040787 A CN201810040787 A CN 201810040787A CN 108312371 A CN108312371 A CN 108312371A
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- speed
- cutting
- sawing process
- wire sawing
- saw
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B28—WORKING CEMENT, CLAY, OR STONE
- B28D—WORKING STONE OR STONE-LIKE MATERIALS
- B28D5/00—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor
- B28D5/04—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor by tools other than rotary type, e.g. reciprocating tools
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B28—WORKING CEMENT, CLAY, OR STONE
- B28D—WORKING STONE OR STONE-LIKE MATERIALS
- B28D5/00—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor
- B28D5/0058—Accessories specially adapted for use with machines for fine working of gems, jewels, crystals, e.g. of semiconductor material
- B28D5/0064—Devices for the automatic drive or the program control of the machines
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- Mechanical Engineering (AREA)
- Finish Polishing, Edge Sharpening, And Grinding By Specific Grinding Devices (AREA)
Abstract
The invention discloses a kind of closed speed control methods of wire sawing process, workpiece is acquired in real time by dynamometer by force information, it is compared by control unit to currently acquiring power and preset reference load, calculate the regulated quantity of scroll saw speed, the output rotating speed for controlling motor drive module adjustment Rolling motor, to realize scroll saw speed control in wire sawing process.The invention also discloses the control systems used in this method.The present invention can carry out real-time monitoring to the saw silk speed of wire sawing process, realize the constant control of cutting force in wire sawing process, both it is avoided that cutting from excessive generation saw silk fracture, it is sliced crackle caused by the microvibration for being avoided that lathe again, ensures the stability and precision of slice surface quality during cutting processing.
Description
Technical field
The invention belongs to wire sawing technology fields, and in particular to a kind of closed speed control system of wire sawing process
System, has further related to its control method.
Background technology
In recent years, modern information industry develops rapidly, and the semi-conducting materials such as silicon and silicon carbide are as IC industry
Important materials application it is increasingly extensive, the purity, surface quality, required precision of semi-conducting material are also increasingly stringenter.
Saw blade cutting machine is current most widely used cutting equipment, which can only be in feed speed and scroll saw speed etc.
The processing being sliced in the case that technological parameter is constant, but in the cutting process of scroll saw constant airspeed, cutting output is generally few
In the amount of feeding, cutting diameter is changing always, and the contact arc length and cutting force between workpiece and scroll saw are in lasting variation
The microvibration of trend, lathe may result in chip crackle, and fast-developing so that wafer perimeter crackle increases.Cutting process
Middle scroll saw with chip friction, causes chip to be broken into polylith along crackle always, is unable to get complete subsequent technique and can be used for being sliced.
In addition, for reciprocating saw blade cutting, when saw blade cutting lathe cuts workpiece material, saw silk exists during the motion frequently to be changed
To cutting force mutation；Scroll saw, which is generated during commutation by instant impact, to snap, and slice easily collapses broken；Wire sawing process
In, the contact arc length moment of scroll saw and workpiece material changes, and cuts fluctuation, and slice surface flatness is insufficient.Entire
Due to many factors in cutting process, such as the abrasion of scroll saw, the vibration of lathe, the concentration of cutting fluid, scroll saw tensile force one
A little X factors etc. are likely to that sawing force is caused to change.
According to construction requirement, the precision of slice preferably must be held in certain range, and existing saw blade cutting is for cutting
The control of power cannot all reach ideal state.Cutting force cross conference so that chip is collapsed broken, scroll saw is easy to wear or even snaps, influence work
The surface quality of part material increases the overall cost of saw blade cutting processing.Cutting force is too small to cause clipping time long, influence
The whole efficiency of cutting processing.Therefore, so that the cutting force in control cutting process is kept stabilization is to ensure that workpiece material is cut
Cut the urgent problem to be solved of quality.
Invention content
It is an object of the present invention to provide a kind of closed speed control method of wire sawing process, to saw silk speed into
Row real-time monitoring solves the problems, such as that current wire sawing process is unable to control cutting force to maintain constant cutting force.
It is a further object of the present invention to provide a kind of closed speed control systems of wire sawing process.
The principle of the present invention is that the information of workpiece institute stress is transmitted to control unit by dynamometer, and control unit is to working as
Preceding acquisition power and preset reference load are compared, it is determined whether are needed to adjust scroll saw speed, then controlled motor driving
Module adjusts the rotating speed of Rolling motor, and then realizes the control to cutting force.
Therefore, first technical solution of the present invention is a kind of closed speed control side of wire sawing process
Method includes the following steps：
Step 1, start control system, setting is with reference to the cutting force Fr and error n of permission.
Step 2, start saw blade cutting machine and saw blade cutting is carried out to workpiece, in cutting process, at interval of certain time by surveying
Power instrument acquires the normal force Fn suffered by workpiece in cutting process, and sends control unit to.
Step 3, after control unit receives the data of dynamometer, cutting force deviation e (k), e (k)=Fn-Fr, if │ are calculated
E (k) │≤n then maintain current scroll saw speed constant；If e (k) ＞ n, control unit calculates scroll saw speed adjusted value Vs, then
The rotating speed of the Rolling motor of control line saw cutting machine is increased to Vs (k), to make cutting force be reduced in the range of permission；Instead
It, the rotating speed for controlling Rolling motor is reduced to Vs (k), to make cutting force be increased in the range of permission.
Wherein, there are two types of the computational methods of scroll saw speed adjusted value Vs (k), one kind is pid control law, and one kind is minimum side
Poor adaptive control law.
(1) calculating process of PID control is as follows：
E (k)=Fn(k)-Fr
up(k)=[kc*e(k)]
U (k)=up(k)+uI(k)+uD(k)
Vs(k)=u (k)
In formula, kcIndicate that controller gain, e (k) indicate cutting force deviation, Δ t is the sampling interval duration of controller, Ti
For integral coefficient, TdFor differential coefficient.
(2) minimum variance adaptive control calculating process is as follows：
System model is
A(z-1)Fn(k)=z-1B(z-1)Vs(k)+ξ(k)
Fn(k)+a1Fn(k-1)+a2Fn(k-2)=b0Vs(k-1)+b1Vs(k-2)+ξ(k)a2,f0=b0,f1=b1
Wherein,
A(z-1)=1+a1z-1+a2z-2
B(z-1)=b0+b1z-1,b0≠0
C(z-1)=1
E(z-1)=1
G(z-1)=g0+g1z-1
F(z-1)=f0+f1z-1
It is Diophantine equations according to the following formula
C(z-1)=A (z-1)E(z-1)+z-1G(z-1)
F(z-1)=B (z-1)E(z-1)
：g0=-a1,g1=-a2,f0=b0,f1=b1
Therefore：
Correspondence system according to orber identification scroll saw speed in System Discrimination and cutting force composition is second-order system, in formula
a1,a2,b0,b1It is the systematic parameter obtained using forgetting factor least squares algorithm realization on-line identification, Fn(k) the k moment is indicated
Cutting force, Fn(k-1) cutting force at (k-1) moment, V are indicateds(k-1) indicate that the scroll saw speed at (k-1) moment, ξ (k) indicate system
Noise jamming in system and vibration error, Vs(k) the scroll saw speed that the expression k moment exports.
The control method of the present invention is suitable for a variety of saw blade cutting machines, and such as reciprocating saw blade cutting machine, multiple wire system scroll saw are cut
Cutting mill, Wire EDM, free abrasive wire saw cutting or diamond wire saw cutting machine etc..
Another technical solution used in the present invention is a kind of closed-loop speed of wire sawing process for the above method
Control system, the control system include the dynamometer being mounted on workpiece to be cut and control unit, and control unit includes number
Speed adjusting module according to capture card and for controlling Rolling motor real-time speed regulating, data collecting card are connected with dynamometer, speed adjusting module
It is connected with the motor drive module of saw blade cutting machine.
Wherein, speed adjusting module includes microcontroller, RS232 serial ports, energy supply control module and link block.
The preferred three-way piezoelectric formula dynamometer of dynamometer.
The invention has the advantages that the closed speed control method and control system of the present invention can be to wire sawing process
Saw silk speed carry out real-time monitoring, realize wire sawing process in cutting force constant control, be both avoided that cutting from excessive
Saw silk fracture occurs, and is sliced crackle caused by being avoided that the microvibration of lathe, ensures slice surface during cutting processing
The stability and precision of quality.
Description of the drawings
Fig. 1 is the structural schematic diagram of the reciprocating consolidated diamond abrasive grain saw blade cutting machine of embodiment；
Fig. 2 is the structural schematic diagram of closed speed control system of the present invention；
Fig. 3 is the structural schematic diagram of control unit in closed speed control of the present invention；
Fig. 4 is the schematic diagram of speed adjusting module in closed speed control of the present invention；
Fig. 5 is the flow diagram of closed speed control method of the present invention.
In figure, 1. lathes, 2. rollers, 3. scroll saws, 4. motors, 5. dynamometers, 6. workpiece, 7. encoders, 8. plankers.
Specific implementation mode
Present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited to
These embodiments.
Closed speed control system of the present invention is used for the control of reciprocating consolidated diamond abrasive grain saw blade cutting machine, back and forth
Formula consolidated diamond abrasive grain saw blade cutting machine is expensive commonly used in semi-conducting materials and sapphire etc. such as cutting silicon crystal, silicon carbide
Weight hard brittle material.The structure of the reciprocating consolidated diamond abrasive grain saw blade cutting machine is as shown in Figure 1, including horizontal positioned planker
8, one end of planker 8 is equipped with motor 4, and motor 4 drives the main axis of roller 2 to control and cut into workpiece 6 by shaft coupling
The speed of the scroll saw 3 of type realizes the feedback to scroll saw speed in the position installation rotary encoder 7 being connected with roller.
The concrete structure of the cutting machine is that motor 4 is connected with belt wheel a by main shaft, and belt wheel a passes through belt band movable belt pulley b
Rotation, belt wheel b is parallel with the axis a of belt wheel a and is located at the underface of belt wheel a, and belt wheel c is connected with belt wheel b by main shaft b, band
It takes turns c to rotate with movable belt pulley d by belt 2, realizes two-stage transmission.One end of ball-screw is socketed on belt wheel d and passes through leading screw
Nut seat d supports, ball-screw are arranged in parallel with planker, are provided with feed screw nut seat below planker, motor driving drum passes through
Belt wheel drives ball-screw to realize that planker moves left and right.
Wherein, planker 8 is horizontally disposed, and the both ends of planker are respectively arranged with bearing a, b and bearing c, d, bearing a, c and branch
It is connected by two polished rods being mutually parallel between seat b, d, planker bottom is respectively uniformly distributed and is arranged two there are six sliding shoe
On bar polished rod, fixation is bolted with planker in sliding shoe.It feed screw nut seat and is fixedly arranged on machine body, and feed screw nut
The position of seat central axis keeps in the same plane and mutually flat with the axial centerline of ball-screw and polished rod bearing
Row.
In order to enable reciprocating consolidated diamond abrasive grain saw blade cutting machine to realize, scroll saw is adjusted, by original stepper motor
110HS20 replaces with DC MOTOR 08SGN motors.
Three-way piezoelectric formula dynamometer 5 is loaded on by fixture by cutting workpiece 6, dynamometer model GAMMA-R-8-
2-M1 can measure X, the power in tri- directions Y, Z, measurement range F respectivelyX、、FYFor ± 65N, FZFor ± 200N, sample frequency is set
It is set to 1KHz.Dynamometer is used to export cutting force suffered in (monitoring in real time) wire sawing process.Concrete principle is, first
Output analog voltage V corresponding with cutting force, signal condition box is by measured signal (i.e. analog voltage V) by amplifying, filtering
Digital signal U is converted into cutting force F Deng operating.
Control unit includes data collecting card and speed adjusting module, and data collecting card uses NI USB-6251 data collecting cards,
And be connected with dynamometer by signal condition box, receive the collected data of dynamometer.As shown in Figure 2,3, speed adjusting module includes
MAX 5418, STC15W404-PLC, RS232 serial ports, power supply control and link block, the electricity of speed adjusting module and saw blade cutting machine
Machine driver is connected, the real-time speed regulating for controlling motor, and Fig. 4 is the schematic diagram of speed adjusting module.The present embodiment control unit is also
Include the inverting module for controlling motor reciprocating motion, inverting module includes Hall sensor, intermediate relay and power supply dress
It sets.Hall sensor uses NJK-5001C type Hall sensors, is mounted on the side of planker, is connected with motor driver, uses
It is limited in motor positive and inverse, to realize the reciprocating cutting of single line.
The present embodiment cuts monocrystalline silicon with reciprocating consolidated diamond abrasive grain saw blade cutting machine-cut, wire saw diameters 0.18mm,
It in cutting process, is controlled using control system of the present invention, control process such as Fig. 5：
(1) start control system, set with reference to cutting force Fr as 1N, the error n of permission is ± 10%.
(2) start Rolling motor and saw blade cutting is carried out to workpiece, in cutting process, one is acquired by dynamometer at interval of 0.2s
Normal force Fn in secondary cutting process, and send control unit to.
(3) control unit calculates cutting force deviation e (k), and e (k)=Fn-Fr maintains current scroll saw if │ e (k) │≤n
Speed is constant；If e (k) ＞ n, control unit calculate scroll saw speed adjusted value Vs (k), then write to speed adjusting module transmission
Wiper orders are communicated using RS232 serial ports, are switched the resistance value that digital potentiometer (MAX5481) seals in circuit in real time, are led to
Extra pulse width modulated (i.e. PWM) increases duty ratio, improves the rotating speed of Rolling motor to Vs (k), to make cutting force be reduced to
In the range of permission.The rotating speed of the motor of control line saw cutting machine increases, to；Conversely, modulating (i.e. PWM) by pulse width
Reduce duty ratio, reduces the rotating speed of Rolling motor to Vs, to make cutting force be increased in the range of permission.Then after 0.2s again
The cutting force data that secondary basis receives judges whether to need to adjust, and closed-loop control is formed with this, makes in cutting force formula in steady
Determine state.
The computational methods of the present embodiment scroll saw speed adjusted value Vs (k) use pid control law.
E (k)=Fn(k)-Fr
up(k)=[kc*e(k)]
U (k)=up(k)+uI(k)+uD(k)
Vs(k)=u (k)
In formula, kcIndicate that controller gain, e (k) indicate cutting force deviation, Δ t is the sampling interval duration of controller, i.e.,
0.2s, TiFor integral coefficient, TdFor differential coefficient.
It is adjusted altogether in the entire cutting process of the present embodiment 18000 times, power belongs to stable in this whole process, adjustment
Success.Control method through the invention, cutting force realization is constant, and the surface roughness of silicon wafer is consistent, can reach micron very
To being Nano grade.
The control system and control method of the present invention can be used for the mechanical, electrical spark wire cutting of multiple wire system saw blade cutting, dissociate
A variety of saw blade cutting machines such as w ire s aws h cutting, diamond wire sawing.If the included motor of saw blade cutting machine is unable to timely adjustment
Scroll saw, then needing to be replaced with according to machine tool capability can be with the motor of timely adjustment scroll saw speed, such as variable-frequency motor, variable-frequency electric
Machine can in its speed adjustable range can arbitrary speed governing, and motor will not damage.
Claims (6)
1. a kind of closed speed control method of wire sawing process, which is characterized in that include the following steps：
Step 1, start control system, setting is with reference to the cutting force Fr and error n of permission；
Step 2, start saw blade cutting machine and saw blade cutting is carried out to workpiece, in cutting process, at interval of certain time by dynamometer
The normal force Fn suffered by workpiece in cutting process is acquired, and sends control unit to；
Step 3, after control unit receives the data of dynamometer, cutting force deviation e (k), e (k)=Fn-Fr, if │ e (k) are calculated
│≤n then maintains current scroll saw speed constant；If e (k) ＞ n, control unit calculates scroll saw speed adjusted value Vs, then controls
The rotating speed of the Rolling motor of saw blade cutting machine is increased to Vs (k), to make cutting force be reduced in the range of permission；Conversely, control
The rotating speed of Rolling motor processed is reduced to Vs (k), to make cutting force be increased in the range of permission.
2. the closed speed control method of wire sawing process according to claim 1, which is characterized in that the scroll saw speed
The computational methods for spending adjusted value Vs (k) are pid control law,
E (k)=Fn(k)-Fr
up(k)=[kc*e(k)]
U (k)=up(k)+uI(k)+uD(k)
Vs(k)=u (k)
In formula, kcIndicate that controller gain, e (k) indicate cutting force deviation, Δ t is the sampling interval duration of controller, TiFor product
Divide coefficient, TdFor differential coefficient.
3. the closed speed control method of wire sawing process according to claim 1, which is characterized in that the scroll saw is cut
Cutting mill is reciprocating saw blade cutting machine, the mechanical, electrical spark wire cutting of multiple wire system saw blade cutting, free abrasive wire saw cutting or diamond
Saw blade cutting machine.
4. a kind of closed speed control system of wire sawing process, which is characterized in that the control system includes being mounted on to wait for
The dynamometer and control unit on workpiece are cut, control unit includes data collecting card and for controlling Rolling motor real-time speed regulating
Speed adjusting module, data collecting card is connected with dynamometer, and speed adjusting module is connected with the motor drive module of saw blade cutting machine.
5. the closed speed control system of wire sawing process according to claim 4, which is characterized in that the speed governing mould
Block includes microcontroller, RS232 serial ports, energy supply control module and link block.
6. the closed speed control system of wire sawing process according to claim 4, which is characterized in that the dynamometer
For three-way piezoelectric formula dynamometer.
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| CN201810040787.2A CN108312371A (en) | 2018-01-16 | 2018-01-16 | A kind of the closed speed control system and control method of wire sawing process |
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| CN201810040787.2A CN108312371A (en) | 2018-01-16 | 2018-01-16 | A kind of the closed speed control system and control method of wire sawing process |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109297798A (en) * | 2018-08-29 | 2019-02-01 | 中国石油大学(北京) | The method for removing core sample skin damage |
| CN110039671A (en) * | 2019-04-24 | 2019-07-23 | 宇晶机器（长沙）有限公司 | A kind of robust multi-line cutting machine Trace speed control system |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102233620A (en) * | 2010-04-28 | 2011-11-09 | 云南中科鑫圆晶体材料有限公司 | Method for controlling multi-wire cutting load |
| CN202137860U (en) * | 2011-06-08 | 2012-02-08 | 西安理工大学 | Adaptive system with reciprocating type scroll saw for cutting hard and brittle materials |
| CN105033352A (en) * | 2015-03-12 | 2015-11-11 | 浙江晨龙锯床股份有限公司 | Band sawing machine constant power sawing control method and intelligent band sawing machine thereof |
| US20160243725A1 (en) * | 2013-09-24 | 2016-08-25 | Commissariat A L'energie Atomique Et Aux Energies Alternatives | Method and device for wire cutting of a material |
-
2018
- 2018-01-16 CN CN201810040787.2A patent/CN108312371A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102233620A (en) * | 2010-04-28 | 2011-11-09 | 云南中科鑫圆晶体材料有限公司 | Method for controlling multi-wire cutting load |
| CN202137860U (en) * | 2011-06-08 | 2012-02-08 | 西安理工大学 | Adaptive system with reciprocating type scroll saw for cutting hard and brittle materials |
| US20160243725A1 (en) * | 2013-09-24 | 2016-08-25 | Commissariat A L'energie Atomique Et Aux Energies Alternatives | Method and device for wire cutting of a material |
| CN105033352A (en) * | 2015-03-12 | 2015-11-11 | 浙江晨龙锯床股份有限公司 | Band sawing machine constant power sawing control method and intelligent band sawing machine thereof |
Non-Patent Citations (1)
| Title |
|---|
| 王树青: "《生化过程自动化技术》", 31 May 1999, 化学工业出版社 * |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109297798A (en) * | 2018-08-29 | 2019-02-01 | 中国石油大学(北京) | The method for removing core sample skin damage |
| CN110039671A (en) * | 2019-04-24 | 2019-07-23 | 宇晶机器（长沙）有限公司 | A kind of robust multi-line cutting machine Trace speed control system |
| CN110039671B (en) * | 2019-04-24 | 2021-01-22 | 宇晶机器（长沙）有限公司 | Robust multi-wire saw wiring speed control system |
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