WO1994004310A1

WO1994004310A1 - Clamp method for preventing deformation of workpiece

Info

Publication number: WO1994004310A1
Application number: PCT/JP1993/001146
Authority: WO
Inventors: Hisao Ishii
Original assignee: Fanuc Ltd
Priority date: 1992-08-13
Filing date: 1993-08-13
Publication date: 1994-03-03
Also published as: JP3051576B2; JPH0655408A

Abstract

A clamp method is provided to promote automation and energy saving in an NC machine tool and accomplish high precision automatic machining. According to this method, a workpiece liable to deformation is firmly clamped without causing clamping forces to bring about its deformation that may cause inaccuracy in machining. First, a work to be machined in accordance with an instruction of an NC machine (24) is placed on a work table. A plurality of machining positions on the workpiece are measured by a touch probe (28) before and after the workpiece is set on a clamping device (30) provided to the work table. The quantity of displacement of each machining portion is computed by comparison/computation portion (46) on the basis of the measurement data (50), and is compared with an allowable displacement quantity stored in a memory unit (42), in order to determine a maximum allowable clamp force of the clamping device (30) for each of a plurality of machining portions so that the displacement quantity does not exceed the allowable value. When NC machining is carried out, the clamping device (30) is set for the maximum allowable clamp force control of the clamp control unit (48) in such a manner as to correspond to the movement of the machining portions. The clamping force may be varied depending on actual clamping conditions.

Description

Description Clamping method for work deformation prevention

The present invention relates to a clamping method for preventing a workpiece to be machined from being excessively deformed in a machine tool. More specifically, the present invention relates to an NC machine tool, which is capable of reducing the amount of deformation of a workpiece generated when a hollow, small, or thin-walled flexible workpiece is clamped on a work table by a clamping device. , Automatically detected before starting NC machining for each machining area, and the maximum allowable clamping force of the clamping device is determined for each machining area within the range where this deformation does not exceed the allowable value. By automatically changing the clamper of the clamp device according to the processing area according to the above determination, a method for preventing deformation of the workpiece to be processed that enables high-precision automatic machining with workpiece deformation within an allowable range About. Background art

When performing machining, it is necessary to firmly support the affected workpiece on the work table against the cutting force of the tool. Therefore, generally, in a machine tool, a clamp device for fixing and supporting a work is provided on a work table. However, when the work has a hollow shape or a small or thin flexible shape, the work may be deformed by the clamping force of the clamp device. When performing automatic machining with an NC machine tool, deformation of the workpiece due to the clamping force will adversely affect machining accuracy. NC machine tools perform automatic machining of workpieces according to NC programs stored in advance. Therefore, if the workpiece is deformed during clamping, there will be a gap between the machining area specified by the coordinate values in the NC program and the machining area on the workpiece to be actually machined. Shape and processing accuracy cannot be obtained.

Conventionally, in order to avoid such a problem, a method of appropriately adjusting a clamp position and a clamper by a clamp device according to a material and a shape of a workpiece to be processed has been generally performed. For example, for a workpiece with a material and shape that does not cause deformation even if the clamping force is large, the workpiece is fixed with sufficient force to perform stable processing, while, for example, a small thin-walled shape that easily deforms For workpieces of the same type, the clamping force is determined in advance and adjusted for each workpiece, such as reducing the clamping force to the limit where machining can be performed in order to ensure processing accuracy. Processing accuracy can be obtained. In addition, while the machining part moves on one workpiece, the appropriate clamping force at the previous machining part becomes inappropriate (large deformation or weak clamping force) at the next machining part. In this case, in this case, stop machining and adjust the clamping force appropriately, or move the clamp position on the workpiece to minimize the amount of deformation in the machined part and ensure that there is sufficient clamping force. After the application, processing may be performed. In these methods, the adjustment of the clamping force of the clamping device is performed, for example, by adjusting the bolt fastening force in the case of a bolt fastening type, and by adjusting the supply pressure in the case of a hydraulic or pneumatic type.

As described above, the deformation of the work caused by the clamping force of the clamping device is a factor that lowers the processing accuracy in the dynamic processing, but on the other hand, in order to perform the stable processing, it is a force that can withstand the cutting force. —It is essential to secure In particular, as the demand for precision machining of small, thin-walled workpieces has increased as in today, deformation of the workpieces has been minimized. Fixing and supporting the work with sufficient force while minimizing it is an essential requirement for improving machining accuracy. In addition, shortening the machining time per unit work and setting up various types of NC machining processes, including the use of ATC (Automatic Tool Change) and the use of robots in machining centers, such as cutting and uncutting of workpieces. When trying to achieve labor savings, changing the clamping position during the machining process or adjusting the clamping force for each work or added part generally requires the intervention of human work. It will hinder. Disclosure of the invention

An object of the present invention is to reliably fix a workpiece having a shape that is easily deformed without lowering the processing accuracy due to the deformation of the workpiece due to the clamping force, thereby promoting automation and labor saving in NC machine tools. It is another object of the present invention to provide a workpiece deformation preventing clamp method which enables high-precision automatic machining.

In order to achieve the above object, the present invention relates to a method for clamping a workpiece to prevent deformation of a NC machine tool, comprising the steps of: a) placing a workpiece to be machined in accordance with a command of an NC device on a work table in a predetermined machining posture; B) Calculate the displacement of each machining part by comparing the positions of multiple machining parts on the work before and after clamping the work with the clamp device provided on the work table, c) The displacement calculated in each of the machining parts is compared with a predetermined displacement allowable value stored in advance in the NC device.d) Within a range where the displacement does not exceed the allowable displacement, Determine the maximum allowable clamping force of the clamp device for each and store it in the NC device.e) When performing NC machining, clamp the clamp device according to each of a plurality of machining parts by fingering of the NC device. Maximum power allowed clan Set the force, and continuously with the movement of the processing site The present invention provides a method including each step of clamping a work in a predetermined machining posture by changing the work position.

The amount of deformation of the work that occurs when the work is clamped on the work table by the clamp device is calculated as the amount of displacement before and after clamping at a plurality of machining sites on the work. The calculated displacement for each machined part is compared with the specified displacement tolerance in the NC unit, and if it exceeds the tolerance, the clamping force of the clamp device is changed so that the displacement is less than the tolerance. . In this way, the maximum allowable clamping force of the clamping device for reducing the work deformation amount to the allowable value or less for each of the plurality of machined parts is determined. The NC device stores the maximum allowable clamping force for each processing portion, and operates the clamping device so as to clamp the workpiece with the maximum allowable clamping force corresponding to each processing portion when performing NC processing. When the machined part moves to the next part, the clamping force of the clamping device is changed to the maximum allowable clamp force corresponding to the next machined part, and the workpiece is continuously clamped. All these operations are performed automatically by the command of the NC device of the NC machine tool.

In the above method, step b) is performed by: f) measuring the positions of a plurality of machining sites on the workpiece by a measuring instrument equipped on the NC machine tool before clamping the workpiece by the clamping device provided on the work table; g) Clamps the workpiece with the clamp device, h) Measures the positions of multiple machining sites with the measuring device while being clamped by the clamp device, and i) Based on the measured values before and after the clamp Each step of calculating the displacement amount of each of the plurality of processing parts in the NC device can be included. In this case, the measuring device may consist of a touch probe attached to the spindle of the NC machine tool.

In step d), j) the workpiece is clamped in a predetermined machining posture by continuously changing the clamping force of the clamping device, and k) a plurality of The method may include a step of determining a maximum clamping force within a range in which a displacement amount does not exceed a displacement allowable value for each of the joint portions, and storing the maximum clamping force in the NC device as a maximum allowable clamping force. BRIEF DESCRIPTION OF THE FIGURES

The above and other objects, features, and advantages of the present invention will be described based on embodiments shown in the accompanying drawings. In the accompanying drawings;

FIG. 1 is a functional block diagram of an NC device for implementing the clamping method according to the present invention,

FIG. 2 is a schematic diagram of a vertical NC drilling machine to which the method according to the present invention can be applied,

Fig. 3a is a diagram showing a clamp device provided on a work table of the drilling machine of Fig. 2 and a workpiece to be processed clamped by the clamp device in a state before the clamp,

FIG. 3b is a diagram showing the clamp device provided on the work table of the drilling machine of FIG. 2 and the workpiece to be processed clamped by the clamp device in a state after the clamping,

FIG. 4a is a flowchart showing a process of a clamping method according to an embodiment of the present invention.

Figure 4b is a flow chart showing the process following Figure 4a,

Figure 4c is a flowchart showing the process following Figure 4b, Figure 4d is the flowchart showing the process following Figure 4c, and Figure 4e is the flowchart showing the process following Figure 4d. ,

FIG. 4f is a flowchart showing a process following FIG. 4e, and FIG. 4g is a flowchart showing a process following FIG. 4f. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail based on preferred embodiments shown in the accompanying drawings. In the following description, an example in which the clamping method according to the present invention is applied to a vertical NC drilling machine will be described. However, any other type of NC machine tool that clamps a work to be processed on a work table using a clamping device is described. Needless to say, the present invention can be applied to this.

Referring to the drawings, FIG. 2 shows a known vertical NC drilling machine 10 to which the clamping method according to an embodiment of the present invention can be applied. The drilling machine 10 includes a bed 12 installed on the work floor. A column 14 is erected on the bed 12, and the spindle head 16 is supported on the column 14 so as to be movable in the vertical direction (Z-axis direction) in the figure by driving the Z-axis feed motor _Mz . It is. The spindle head 16 rotatably supports the spindle 18 at its front end. The spindle 18 rotates by driving the spindle motor M s, and a tool (not shown) held at the tip of the spindle 18 Performs drilling on the workpiece. Further, the bed 12 supports the saddle 20 so as to be able to be moved by driving a Y-axis feed motor (not shown) in a Y-axis direction orthogonal to the Z-axis. In addition, a work table 22 is provided on the upper surface of the saddle 20 so as to be able to move by driving an X-axis feed motor (not shown) in the X-axis direction orthogonal to both the Z-axis and the Y-axis. You. As described above, the main shaft 18 and the work table 22 can be relatively moved in an orthogonal three-axis coordinate system including the X-axis, the Y-axis, and the Z-axis, which are orthogonal to each other.

The drilling machine 10 includes an NC device 24 that performs various control operations in NC machining such as a feed operation in accordance with an NC program. An NC program 26 that numerically represents command information such as position coordinates, a feed speed, and a rotation speed of a tool is generally created on an NC tape and then input to the NC device 24. The drilling machine 10 is equipped with an automatic tool changer (ATC: not shown). Therefore, a desired tool can be automatically attached to and detached from the spindle 18 from a plurality of tools stored in a tool magazine (not shown), and can be replaced. In the tool magazine, together with various tools, an evening probe 28 (see Fig. 3) used for measuring the surface position of the workpiece to be machined, such as a machining reference point, is housed. Detachable. As shown in FIG. 3, a clamp device 30 for clamping a workpiece W is provided on a work table 22 of the drilling machine 10. The clamp device 30 includes a base 32 fixed to the work table 22, a claw 34 in contact with the work W, and a cylinder 36 for moving the claw 34 with respect to the base 32. And The cylinder 36 is operated, for example, by hydraulic pressure or air pressure, and can clamp the workpiece W with a clamping force that can oppose the cutting force during machining, and can change the clamper as desired.

When a thin work W as shown in FIG. 3A is clamped by the clamp device 30, the work W is deformed by the clamper of the clamp device 30 as shown in FIG. If machining is performed in this state, there will be a deviation between the coordinate values of the machining area in the NC program and the actual coordinate values of the machining area on the workpiece W to be actually machined, due to the deformation of the workpiece. Is a problem with conventional NC machine tools. Therefore, in the present invention, the above-mentioned displacement, that is, the amount of displacement due to the clamping force at the machined portion of the workpiece W is measured and calculated before the machining is performed, and the maximum amount of the displacement within a range that does not exceed a predetermined allowable value is measured. Determine the allowable clamping force, and perform NC machining while clamping the workpiece W with the maximum allowable clamping force corresponding to the machining area. Hereinafter, an embodiment of the present invention will be described with reference to the block diagram of FIG. 1 and the flowcharts of FIGS. 4A to 4G.

As shown in FIG. 1, a method for implementing the clamping method according to the present invention is described. The NC unit 24 includes an input unit 38 for inputting an NC program 26 having NC command data such as a tool operation mode, a moving position, and a feed speed, and an NC input from the input unit 38. An arithmetic control unit 40 that performs calculations such as positioning and interpolation based on command data, a storage unit 42 that records calculation results and control programs, and a feed drive motor and spindle motor for each axis based on the calculation results This is a well-known NC device including a servo control unit 44 for controlling the control. In practicing the present invention, the NC device 24 calculates the amount of displacement of the workpiece clamped by the clamp device on the worktable at a plurality of machining sites, and stores the amount of displacement in the storage unit 4. A comparison calculation unit 46 for comparing with the predetermined displacement allowable value recorded in 2 and a maximum allowable clamper is determined based on the calculation result of the comparison calculation unit 46, and a clamping device is And a clamp controller 48 for setting and changing the clamper 30 to the maximum allowable clamping force. According to a preferred embodiment of the present invention, the data 50 for calculating the work displacement amount is obtained by using the touch probe 28 attached to the tip of the spindle to obtain the coordinate values of the work site of the work before and after clamping. That is, it is obtained by measuring before and after deformation. Hereinafter, with reference to FIGS. 4A to 4G, a series of processes of the clamping method according to an embodiment of the present invention will be described.

As shown in Fig. 4a, as a preparation work, the NC program 24 and the NC program 26 and the allowable displacement (X, «a, az) at each machining site are input to the NC device ₂₄ , and the work table ₂₂ is displayed. Place the workpiece W at the predetermined position in the same posture as when processing is performed, and press the start button of the NC device 24. Thus, the machining operation of the drilling machine 10 is started. In the present invention, first, in step 61, the evening probe 28 is attached to the spindle 18 by the automatic tool changer. Here, the clamp device 30 is released (step 62), and the work W is kept in a deformed state (see FIG. 3A). Next, in step 63, the evening probe 28 is first approached from the X-axis direction to the machining site on the workpiece W based on the machining site coordinate value data (ΧΡ, ,, ZP) of the NC program 26 (that is, the X-axis and by operating the delivery driving motor of the Y-axis is moved toward the point X = chi [rho spindle 1 8 Upsilon = Upsilon _[rho straight line), to determine if it can reach the machining area (evening Tsuchipurobu 2 The direction in which 8 is moved is the positive direction of the X axis.) Here, in the present embodiment, since drilling with an NC drilling machine is assumed, the processing portion is not arranged on the end face of the workpiece W, and the processing surface is generally orthogonal to the feed direction of the spindle 18, that is, the Ζ-axis direction. X—parallel to the Υ plane. Therefore, it is practically impossible for the above method to accurately reach the workpiece probe 28, and therefore, the predetermined tolerance 2 is set, and the location of the workpiece probe 28 in contact with the workpiece W is set. If the coordinates are within two tolerances (that is, ステップ Ρ-α ≤ X ≤ Xp + in step 63), it is determined that the workpiece can be reached.

In this way, when it is determined that the workpiece can be approached from the X-axis direction, the evening probe 28 touches the workpiece W in step 64.

Stop the feed movement of spindle 18 at the position where the switch was turned on. On the other hand, if it is determined that the workpiece cannot be approached from the X-axis direction, in step 65, the YUTSU probe 28 is slightly shifted in the Y-axis direction to approach the workpiece W in the X-axis direction in the same manner. Abuts on workpiece W near machining area

Stop the feed movement of spindle 18 at the position where the switch was turned on. At this point, when the touch probe 28 is turned ON and the movement of the spindle 18 stops, the X coordinate value X, at this time, is recorded in the storage unit 36 of the NC device 24 in step 66. Similarly, as shown in Fig. 4b, the Y coordinate value at the processing part or at one point near the processing part is measured and recorded at steps 67 to 70, and the Z coordinate value is similarly calculated at steps 71 to 74. Measure and record the value Z i.

In each of the steps up to this point, the position coordinate value (X,, Yi, Za) of the processing position on the work W without deformation before being clamped by the clamping device 30 on the work table 22 or a point near the processing position. Is measured and recorded. Therefore, next, the work W is firmly clamped at the same position on the work table 22 in the same posture by the maximum clamper of the clamp device 30 (step 75).

Subsequently, as shown in FIG. 4c, in step 76, the evening probe 28 is first moved from the X-axis direction based on the coordinate values (X,, Υ,, Z i) of the machined part measured before clamping. Close to this measurement position (that is, actuate the X-axis and Y-axis feed drive motors to move the spindle 18 to the point Χ = Χ, on the line of Y = Y,), Stops the feed movement of the spindle 18 at the position where it contacts the workpiece W (switch ON). Then, in step 77, the X coordinate value X ₂ at this time is recorded in the storage unit 36 of the ΝC device 24. Similarly, Step 7 8, 7 Upsilon coordinates Upsilon ₂ in 1 point machining area or processing site near the clamped measured and recorded at 9, Step 8 0, also measured Zeta coordinates Zeta ₂ 8 1 And record.

In this way, the position coordinate values (X,, ，,, Ζ,) and () before and after clamping (ie, after the displacement) at the machining site of the workpiece W or at one point near the same are determined. When Χ ₂ , Υ ₂ , Ζ ₂ ) are measured and recorded, in step 82, the comparison calculation unit 46 of the NC device 24 calculates the displacement amount (ε _,, ε y, ε ζ), then, the displacement amount (ε X, ε γ, ε ζ) prerecorded displaced allowable value in the storage section 3 6 and the axial component of _(α χ, αν, t) is compared with.

Figure 4 As shown in d, first, in Step 8 3 to compare the X-axis component <comparison result, if the amount of displacement epsilon _chi is greater than the displacement tolerance X, Sutetsu In step 84, it is determined whether or not the deformation of the workpiece due to the clamp has brought the processed part closer to the Tsuchi probe 28, that is, whether or not X ₂ <X 1. If Χ ₂ <Χ, open clamp device 30 in step 85, and fix Utsuchi probe 28 in position X = X i — X on the straight line Υ = Υ! In step 86. I do. In this state, the clamp device 30 is gradually closed in step 87, and when the work W is gradually deformed and comes into contact with the evening probe 28, the closing of the clamp device 30 is stopped.

If it is determined in step 84 that X ₂ <X j is not satisfied, the clamp device 30 is closed in step 88 and the touch probe 28 is moved in step 89 to a straight line of Y = Y, Χ. = Χ, + αχ. In this state, the clamp device 30 is gradually released in step 90, and when the deformed work W is gradually restored and comes into contact with the evening probe 28, the release of the clamp device 30 is stopped. In this way, the maximum clamping force P _x in a range where the X component of displacement amount X _X is equal to or less than the allowable value X is determined, and in step 91, this clamping force P _x is recorded in the storage unit 36 of the NC device. I do.

As a result of the comparison in step 83, if the displacement amount £ _X is smaller than the allowable displacement value _αχ , the clamping force used in step 75 is regarded as the maximum clamping force Px and recorded in the storage unit 36 of the NC device. (Step 92) c Subsequently, as shown in FIG. 4e, in steps 93 to 102, similarly, the maximum clamp force 範_囲範囲 in the range where the Y component ε _{変位} of the displacement amount is equal to or less than the allowable value γ is obtained. Is determined and recorded in the storage unit 36 of the NC device. Further, as shown in Fig. 4f, the maximum clamping force Ρ で in the range where the Z component ε _{変位} of the displacement amount is equal to or less than the allowable value α _で is similarly determined in steps 103 to 112. Recorded in the storage unit 36 of the NC unit.

Finally, as shown in Fig. Puka P x, PY and P z are compared with each other, and the minimum clamping force among them is set as the maximum allowable clamping force P (step 113). In each of the above steps, the maximum allowable clamping force P for one processing part was obtained.In the same manner, the maximum allowable clamping force P for other processing parts was determined, and all of them were stored in the storage unit 36 of the NC unit. Record (steps 114).

Next, at step 115, the automatic probe changer replaces the evening probe 28 attached to the tip of the spindle with a desired tool for machining. Then, in step 1 16, under the control of the clamp controller 48 of the NC device 24, the clamp device 30 is set to the maximum allowable clamping force P to clamp the workpiece W, and then in step 1 17 Perform NC machining. At this time, as the machining area specified in the NC program 28 moves, the clamping device 30 is set as needed to the maximum allowable clamping force determined for the machining area. Change and clamp the workpiece W. In this way, during the execution of the NC machining, the workpiece W can always be reliably clamped by the optimal clamping force that causes deformation below the allowable value in all the machining portions of the workpiece W.

In the above-described embodiment, the work displacement amount calculation data, that is, the coordinate values of the machined parts before and after the clamp or the vicinity thereof were measured using the evening probe 28 for work surface position measurement provided on the NC drilling machine. Based on this, the configuration is such that the coordinate values of the corrected machining site are calculated. However, because the workpiece shape is complicated and the YUTSU probe 28 cannot approach the machined part, and even if a point near the machined part is measured, the error between the obtained displacement and the actual displacement of the machined part is small. May be expected to be large. In such a case, for example, a projection to which the UTSU probe 28 can be brought into contact with the processing surface of the processing portion of the workpiece W is formed by a magnet or the like. A possible method is to measure the position as close as possible to the part to be machined. However, in this method, manual work is required when attaching and detaching the protrusions to and from the work, which hinders complete automation. Therefore, it is convenient to input various data for clamping the workpiece to the NC device 24 and calculate the work displacement amount by a predetermined calculation such as a finite element method. Industrial applicability

As is clear from the above description, the present invention compares the amount of deformation of the work generated when the work to be processed is clamped on the worktable by the clamp device with a predetermined allowable value in the NC device. Determine the maximum allowable clamping force of the clamp device to reduce the amount of work deformation below the allowable value for each of the multiple machining parts, and when performing NC machining, automatically execute the machining part The work piece is clamped by setting and changing the clamp force of the clamp device to the maximum allowable clamping force in accordance with the movement. As a result, according to the clamping method of the present invention, a workpiece having a shape that is easily deformed can be securely fixed without lowering the processing accuracy due to the workpiece deformation due to the clamping force. Therefore, the present invention, when used in an NC machine tool, enables high-precision and high-efficiency automatic machining while promoting automation and labor saving.

Claims

The scope of the claims

1. A method for clamping workpiece deformation in NC machine tools,

a) Place the work to be machined in accordance with the command of the NC device on the work table in the specified machining posture,

b) before and after clamping the workpiece by the clamping device provided on the work table, comparing the positions of a plurality of machining parts on the work to calculate the displacement amount of each machining part;

c) comparing the displacement amount calculated in each of the plurality of machining parts with a predetermined displacement allowable value stored in advance in the NC device,

d) determining a maximum allowable clamp force of the clamp device for each of the plurality of processing parts within a range where the displacement amount does not exceed the displacement allowable value, storing the maximum allowable clamp force in the NC device,

e) When performing the NC machining, the clamping force of the clamping device is set to the maximum allowable clamping force corresponding to each of the plurality of machining sites, according to a command of the NC device, and the movement of the machining region is performed. Continuously changing and clamping the workpiece in the predetermined machining posture.

2. Step b) is performed

f) Before clamping the workpiece by the clamping device provided on the work table, measure the positions of a plurality of machining sites on the workpiece by a measuring instrument equipped on the NC machine tool;

g) clamping the workpiece by the clamping device; h) measuring the positions of the plurality of processing parts by the measuring device while being clamped by the clamping device;

i) Based on the measured values before and after clamping, Calculate the amount of displacement of each processing part in the NC device,

The method of claim 1, comprising each step.

3. The method according to claim 2, wherein the measuring device comprises a touch probe mounted on a spindle of the NC machine tool.

4. Step d) above

j) clamping the workpiece in the predetermined machining position by continuously changing the clamping force of the clamping device;

k) For each of the plurality of machining parts, determine a maximum clamping force within a range where the displacement amount does not exceed the allowable displacement value, and store the maximum clamping force as a maximum allowable clamping force in the NC device. The method of claim 1, comprising: