JPH0818208B2 - Method for determining static pressure of air semi-floating sliding surface of machine tool and its control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a static pressure control device for an air semi-floating sliding surface in a machine tool or various measuring devices equipped with a moving body that moves along a sliding surface. . More specifically, the feed resistance is reduced by supplying pressurized air to the sliding surfaces on which the metal members slide with each other to levitate the moving body. At this time,
The present invention relates to a static pressure control device for an air semi-floating sliding surface having a metal contact portion and an air contact portion on a sliding surface.

"Prior Art" A machine tool or the like in which both members slide with each other, for example, a slide table of a moving body such as a work table on which a work is placed and a slide guide surface of a bed. . The pressure acting on the slide guide surfaces is supported by the static pressure of the pressure fluid supplied between the slide guide surfaces and the direct contact between the moving body and the sliding surface, that is, the solid (metal) friction force. Machines have been proposed (for example, JP-A-54-126850 and JP-A-56-126547).

This proposal adjusts the load fluid that changes according to the weight of the moving body and the work placed on the moving body by the static pressure of the pressure fluid that is supplied between the sliding guide surfaces, and directly adjusts the moving body and the sliding surface. The sliding resistance is automatically controlled to a desired value by dynamic contact, and the static pressure is compensated according to the load. On the other hand, in order to adjust the static pressure, a plurality of stages of static pressure are set in advance for each predetermined weight of the work against the fluctuation of the work weight, and the static pressure is adjusted according to the work weight each time the work weight changes. It is also known to select manually or by programming.

[Problems to be solved by the invention] In particular, as a slide guide surface of a machine tool, 1) a large load is applied to the slide guide surface during rough finishing and heavy cutting, so it is necessary to increase slip resistance and ensure vibration damping capability. Yes, 2) It is necessary to reduce slip resistance and improve feed accuracy during finishing. Thus, two contradictory properties are required. In the static pressure control of the air semi-floating sliding surface of machine tools, it is necessary to readjust the static pressure every time the cutting conditions change from rough cutting to heavy cutting to finishing, which not only complicates the operation but also reduces the work weight. There is a problem that smooth control cannot be performed because a large number of static pressures cannot be set according to the above.

In view of the technical background as described above, the present invention is
The invention has been invented and achieves the following object.

An object of the present invention is to provide a static pressure determination method for a semi-air-floating sliding surface of a machine tool and a control apparatus therefor, which is estimated by the output torque of a servomotor that sends a table to determine the state of the air-floating sliding surface of a machine tool. To provide.

Another object of the present invention is to provide a machine tool for selecting the magnitude of the air pressure to be supplied to the sliding surface after the state of the air semi-floating sliding surface of the machine tool is estimated and judged by the output torque of the servomotor sending the table. An object of the present invention is to provide a static pressure determination method for a semi-floating sliding surface of air and its control device.

Still another object of the present invention is to provide a static pressure determination method for a semi-floating sliding surface of a machine tool and a control device therefor, which is performed by changing the air pressure supplied to the sliding surface in order to prevent vibration of the machine body during cutting. It is in.

Still another object of the present invention is to provide an air semi-floating slide for a machine tool, in which the magnitude of the air pressure supplied to the slide surface in order to keep the state of the air semi-float slide surface of the machine tool optimum. A static pressure determination method for a surface and a control device therefor.

[Means and Actions for Solving the Problems] The following means are adopted to solve the problems.

The static pressure determination method for the air semi-floating sliding surface of a machine tool according to the present invention includes a bed, a table for mounting and moving a work, a feed screw for driving the table, and a rotational drive for driving the feed screw. Of a semi-floating sliding surface of a machine tool comprising a feed servomotor and a pneumatic supply path for supplying compressed air to the sliding surface between the bed and the table, when the workpiece is not machined and the table is fast-fed. At that time, the output torque of the feed servomotor is measured, the magnitude of the air pressure supplied to the sliding surface is selected and supplied by the measured value of the output torque, and the output torque determined during the fast-forwarding of the table is set as a standard value. After the air pressure is determined, the vibration of the table during the cutting of the workpiece is detected, and the detected value vibrates in advance. When more have value by controlling the optimum value of the air pressure is to the air supply.

Further, the state of the slip surface may be estimated by comparing the output torque with a preset threshold value, and the air pressure may be selected and supplied based on this estimation.

A static pressure control device for an air semi-floating sliding surface of a first machine tool of the present invention includes a bed, a table for mounting and moving a work, a feed screw for driving the table, and a feed screw for driving the table. In the air semi-floating sliding surface of the machine tool, which comprises a feed servo motor for rotationally driving, and an air pressure supply path for supplying air pressure to the sliding surface between the bed and the table, the air pressure in the air supply path is selectively A pressure adjusting means for supplying the output torque of the feed servomotor, a torque measuring means for measuring an output torque of the feed servomotor, a torque setting means for setting a threshold value of the output torque of the feed servomotor in advance, and a torque measuring means. Comparing means for comparing the measured value with the set value of the torque setting means; and the pressure adjusting means so that the measured value falls within the set value. A pneumatic selection means for controlling, and a weight measuring means for measuring the workpiece weight the threshold to determine the weight of the workpiece.

A second static pressure control device for a semi-floating sliding surface of a machine tool according to the present invention includes a bed, a table for mounting and moving a work, a feed screw for driving the table, and a feed screw for driving the table. In a pneumatic semi-floating sliding surface of a machine tool, which comprises a feed servo motor for rotationally driving and an air pressure supplying path for supplying air pressure to a sliding surface between the bed and the table, the air pressure in the air pressure supplying path is selectively A pressure adjusting means for supplying the output torque of the feed servomotor, a torque measuring means for measuring an output torque of the feed servomotor, a torque setting means for setting a threshold value of the output torque of the feed servomotor in advance, and a torque measuring means. Comparing means for comparing the measured value with the set value of the torque setting means; and vibration detecting means for detecting the vibration value of the machine body of the machine tool. Vibration setting means for setting a vibration threshold value of the machine body in advance, comparing means for comparing a vibration detection value by the vibration detecting means and a vibration threshold value of the vibration setting means, and the table at the time of fast-forwarding the table. After selecting the air pressure so that the measured value by the torque measuring means falls within the torque setting value, the air pressure is adjusted when the vibration detection value by the vibration detecting means during the work cutting becomes equal to or higher than the vibration threshold value. Air pressure selecting means for controlling the pressure adjusting means so as to reduce the pressure.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an outline of a static pressure control device for an air semi-floating sliding surface. A slip guide surface 2 is formed on the bed 1. The sliding guide surface 2 is a grinding surface, and a table 3 is slidably provided on the sliding guide surface 2. A pocket 4, which is a pneumatic chamber, is formed on the lower surface of the table 3 between the slide guide surface 2 and the table 3.
The work W is clamped on the table 3 by a clamp jig.

The work W is cut by the milling cutter 5. The milling cutter 5 is driven to rotate by a spindle motor 6. These points are well-known structures and functions, and detailed description thereof will be omitted. A feed screw 7 is screwed into a nut (not shown) provided on the table 3, and the feed screw 7 is rotationally driven by a feed servomotor 8. Pressure air is supplied to the pocket 4 through a supply pipe 9 from an electropneumatic pressure proportional valve 10 which is a pressure adjusting means. The electropneumatic pressure proportional valve 10 is a proportional valve for controlling the pressure of compressed air according to the input current.

The electro-pneumatic pressure proportional valve 10 has a known structure and will not be described in detail here. Pressure air is supplied to the electropneumatic pressure proportional valve 10 from a pressure air supply source 11. A current is input to the electropneumatic pressure proportional valve 10 from the air pressure selection circuit 13. Electro-pneumatic pressure proportional valve 10
The compressed air having a pressure proportional to the magnitude of this current flows out. On the other hand, the N / C device 20 is a known numerical control device and controls the movement of the table 3 by a program command or the like.

The feed command from the N / C device 20 is transmitted to the feed servomotor 8 via the amplifier 21. The feed servo motor 8 is
The feed screw 7 is rotationally driven by this feed command to control the movement of the table 3. A current detection circuit 22 is incorporated between the amplifier 21 and the feed servo motor 8, and this current detection circuit 22 detects the input current to the feed servo motor 8 and determines the magnitude of this input current as the magnitude of the voltage. Will be output. The input current to the feed servomotor 8 is proportional to the magnitude of the servomotor output torque. As a result, the magnitude of the input current of the feed servomotor 8 is equal to the magnitude of the output torque of the feed servomotor 8.

The torque level setting circuit 23 is a circuit that generates a constant voltage in response to a signal from the N / C device 20. Fig. 2 (a)
FIG. 4 is a diagram showing a relationship between a feed speed and time when the feed servomotor 8 is activated. The feed rate rises rapidly and becomes constant after a certain time. FIG. 2B shows an example of fluctuations in the torque of the feed servomotor 8 at this time. It can be seen that the torque fluctuates and is unstable when the feed servo motor 8 is started and stopped.

It can be estimated that this is mainly due to the static frictional force on the slip surface, the state of the lubricating oil, and the inertia of the moving body such as the table. This torque is stable in the constant speed region.
This torque can be measured as the input current of the feed servomotor 8 as described above. The torque in this constant speed state is
In the non-cutting state, that is, in the unloaded state, it depends on the work W, the weight of the table, and the state of the sliding surfaces of the table and the bed. The state of the slip surface depends on the coefficient of dynamic friction through the lubricating oil. However, since the influence of the nut and the other sliding surface such as the feed screw 7 is small, it is fixed.

The output torque exceeds the upper threshold value when the area of the metal contact portion increases, and decreases below the lower threshold value when the metal contact portion disappears altogether. After all, it is estimated that the ideal state of the slip surface will be in the middle of this range. The torque level setting circuit 23 is a circuit that generates an upper threshold value and a lower threshold value, and the upper and lower threshold values are set by a command from the N / C device 20. The comparator 24 is a circuit that compares the outputs of the torque level setting circuit 23 and the current detection circuit 22 with the magnitude of the voltage.

The comparator 24 outputs only when the output value from the current detection circuit 22 deviates from the upper and lower thresholds of the torque level setting circuit 23. The output of the comparator 24 is input to the AND circuit 25.
The AND circuit 25 is supplied with a feed current detection circuit valid signal generated by the N / C device 20.

This signal is a signal that is output only when the feed servo motor 8 is fast-forwarded and a constant speed has elapsed, and then a constant speed state is reached. This is the detection time referred to in FIG. If there is an output from the comparator 24 within this detection time, the AND circuit 25 outputs a signal to the OR circuit 34, and the signal is output from the OR circuit 34 to the air pressure selection circuit 13. The air pressure selection circuit 13
In response to this signal, the electropneumatic pressure proportional valve 10 is instructed to either increase or decrease the air pressure.

On the other hand, the vibration sensor 30 is provided on the table 3.
The vibration sensor 30 is a conversion element that generates an electric output in proportion to mechanical vibration. This output is input to the comparator 32 via the amplifier 35. On the other hand, the comparator 32 is also input from the vibration level setting circuit 31. As for the set value of the vibration level setting circuit 31, the threshold value can be freely set from the N / C device 20. This threshold value is set to a level slightly higher than the output value output by the vibration amplitude detected in the normal cutting state. Desirably, it is set to a limit value that is determined as an abnormal vibration amplitude level when the machine tool is in heavy cutting. These values are values that have been confirmed in advance by experiments or the like.

When the vibration sensor 30 detects a vibration amplitude equal to or higher than this vibration level, it outputs it to the comparator 32. The output of the comparator 32 is input to the AND circuit 33. To the AND circuit 33, a signal indicating that the cutting is being performed, that is, a vibration detection valid signal is output from the N / C device 20 during cutting, and a signal is output to the OR circuit 34 when abnormal vibration amplitude occurs. . The OR circuit 34 is
This signal is output to the air pressure selection circuit 13. When this signal is sent, the air pressure selection circuit 13 instructs the electropneumatic pressure proportional valve 10 to lower the air pressure.

Operation FIG. 3 (a) is a flowchart showing an outline of the operation of detecting the feed resistance, that is, the servo motor output torque by the feed servo motor 8. More specifically, the work W is mounted on the table 3 and the feed resistance value of the table 3 is detected when fast-forwarding, and the detected value is used as a standard value to set the air pressure of the pocket 4, that is, the static pressure. It shows the operation. When a fast-forward command (for example, G00 command) is issued from the N / C device 20 to the servo motor 8, the N / C device 20 determines whether it is the detection time.

In other words, the feed servomotor 8 is rotationally driven,
No detection is performed during the time until the fast-forward steady state is reached. This non-detection time is a time determined by the characteristics of the feed servomotor 8, and is set and stored in the N / C device 20 in advance. Alternatively, a method of determining that it is the detection time when the constant speed signal of the feed servo motor 8 is output may be used. The constant-speed signal has this output function in a standard N / C device.

At the detection time, the current detection circuit 22 samples the input current of the feed servomotor 8. The sampled input current data means the output torque of the feed servomotor 8. The magnitude of the input current data is output as a voltage value and compared with the output of the torque level setting circuit 23. The upper and lower thresholds of the torque level setting circuit 23 are the N / C device 20.
The size is set in advance by means such as a program command or keyboard input.

The size of this threshold value is basically determined by the weight of the work W. However, since it is not uniquely determined only by the weight of the work W, an experimental value or an empirical value may be selected. That is, the state of the contact surface between the slide guide surface 2 and the table 3 changes because the weight of the table 3 is constant but the weight of the work W changes. The comparator 24 is
When the output voltage of the current detection circuit 22 exceeds the set threshold value, it is estimated that the sliding surface between the table 3 and the sliding guide surface 2 is in metal contact more than necessary.

When it is below the set threshold value, it is presumed that it is close to complete air levitation. Since the ideal state is the intermediate position, when the upper threshold is exceeded, the comparator 24
Outputs a signal to increase the air pressure, and the air pressure selection circuit 13
To enter. The air pressure selection circuit 13 inputs to the electropneumatic pressure proportional valve 10 that the air pressure should be increased in response to this input signal.

The electro-pneumatic pressure proportional valve 10 supplies the raised air pressure to the pocket 4 via the supply pipe 9. When it is lower than the set threshold value, the comparator 24 conversely generates a signal for lowering the air pressure. The electropneumatic pressure proportional valve 10 supplies the air pressure to the supply pipe 9 to be one step lower. After all, each time the fast-forward command is generated, the optimum air pressure is supplied to the slip surface. Using the static pressure at the time of this rapid feed as a standard, in other words, it is determined that the sliding surface is in a normal state, and processing is started.

FIG. 3 (b) is a flow chart showing an operation of detecting the vibration during cutting and changing the static pressure. When the setting of the air pressure is completed based on the feed torque at the time of fast-forwarding the table, the vibration sensor 30 starts detecting the vibration when the N / C device 20 becomes a program that issues a cutting command (for example, G01). The output value of this vibration sensor 30 is the vibration level setting circuit.
The output value from 31 is compared with the comparator 32, and when a value above the set value is output, this signal is input to the AND circuit 33.

To the AND circuit 33, the N / C device 20 outputs a vibration detection valid signal which means that cutting is being performed. Therefore, the output signal of the comparator 32 is output to the OR circuit 34 and input to the air pressure selection circuit 13. In response to this signal, the air pressure selection circuit 13 operates the electropneumatic pressure proportional valve 10 to reduce the air pressure and increase the ratio of the metal contact area between the slide guide surface 2 and the table 3. After the set time has passed, that is, after the time required for the static pressure to drop and the table 3 to become sufficiently stable (the set time), the N / C device 20 outputs the vibration detection valid signal again and the vibration sensor again. Compare the output of 30 with the set value, and if there is vibration above the set value, reduce the air pressure on the slip surface again. This vibration monitoring works effectively during the cutting block of the program.

[Other Embodiments] In the above embodiment, the feed servo motor 8 during the normal fast-forward operation is used.
The current of is detected and is set as a standard value. As the set value of the torque level setting circuit 23, the weight of the work W is known in advance, and an experimental value or an empirical value is set according to this weight. But work W
Is lighter as it loses weight during processing. Also, to know the weight, it is necessary to measure it in advance. In FIG. 4, the weight of the work W is automatically measured, and the static pressure is controlled by the measured value.

The work W of the normal machining center is mounted on the pallet 40. The pallet 40 is clamped on the table 3 during processing. This clamp is clamped by a hydraulic cylinder 41 provided in the table 3. Hydraulic cylinder 41
The piston rod of the piston 42 has a clamp member 43 at its tip and is clamped on the table 3 by this clamp member. Pressure oil is supplied to the hydraulic cylinder 41 from a hydraulic pressure source 44 via a switching valve 45.

Discharge pipe 46 leading to hydraulic cylinder 41 under piston 42
A pressure sensor 47 is connected to. Pressure sensor 47
Is a sensor composed of a piezoelectric element and measures the magnitude of hydraulic pressure. The output of the pressure sensor 47 is amplified by the amplifier 48 and drives the electropneumatic pressure proportional valve 10. In order to measure the weight of the work W with the pressure sensor 47, the on-off valve 45 is operated to introduce hydraulic pressure into the cylinder chamber below the piston 42. The piston 42 rises and lifts the pallet 40 and the work W.

In this state, the on-off valve 45 is set to the neutral state and both pots are closed, and the pressure sensor 47 measures the hydraulic pressure in the discharge pipe 46. Since this hydraulic pressure is proportional to the weight of the work W, the weight is measured. The air pressure supplied to the sliding surface is controlled according to this weight. Work W on the sliding surface
The air pressure is supplied according to the weight of. Further, in the above embodiment, the upper and lower threshold values are changed by the set value from the N / C device 20. However, as in this embodiment, the weight of the work W may be automatically set, and the threshold value may be automatically set based on this weight.

Although the output torque of the feed servomotor 8 is the input current detected, other known torque detection means such as twisting of the feed screw 7 may be used. Although the vibration sensor 30 detects the vibration of the table 3, the vibration sensor 30 may detect another body portion instead of the table 3.

The table 3 in the above embodiment does not mean only the work table but may be a tool rest or the like. Therefore, the work also has the same meaning here as a turret of a tool rest, a tool, and the like.

[Advantages of the Invention] As described above, the present invention can detect the state of the slip surface by a simple method and can supply the air pressure corresponding to the slip surface, so that the characteristic state of the slip guide surface can be kept good. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram showing the control of a static pressure device for a semi-floating sliding surface of air, FIG. 2 is a diagram showing the change in feed speed and torque of a feed servomotor after starting, and FIG. 3 shows the operation of the device. A flow chart shown in FIG. 4 is an embodiment showing a work weight measuring apparatus. 1 …… Bed, 2 …… Slip guide surface, 3 …… Table,
7 ... Feed screw, 8 ... Feed servomotor, 10 ... Electropneumatic pressure proportional valve, 23 ... Detection level setting circuit, 24 ... Comparator

Claims (4)

[Claims] 1. A bed, a table for mounting and moving a work, a feed screw for driving the table, a feed servomotor for rotationally driving the feed screw, the bed and the table. In the air semi-floating sliding surface of the machine tool, which consists of an air pressure supply path that supplies compressed air to the sliding surface between, while the workpiece is not processed and the table is fast-forwarded, the output torque of the feed servo motor is measured. When the magnitude of the air pressure to be supplied to the sliding surface is selected and supplied according to the measured value of the output torque, and the air pressure is determined using the output torque determined during the fast-forwarding of the table as a standard value, the workpiece is cut. The vibration of the table is detected, and the air pressure is controlled to an optimum value when the detected value is equal to or more than a preset vibration threshold value. Static pressure determination method of an air half floating sliding surface of a machine tool, wherein the air supply Te. 2. The machine tool according to claim 1, wherein the state of the slip surface is estimated by comparing the output torque with a preset threshold value, and the air pressure is selected and supplied based on this estimation. Method for determining static pressure on semi-floating sliding surface of air. 3. A bed, a table for mounting and moving a work, a feed screw for driving the table, a feed servomotor for rotationally driving the feed screw, the bed and the table. In the air semi-floating sliding surface of the machine tool, which comprises an air pressure supply path for supplying air pressure to the sliding surface between the pressure adjusting means for selectively supplying the air pressure of the air supply path, and the output of the feed servomotor. A torque measuring means for measuring a torque, a torque setting means for setting a threshold value of the output torque of the feed servo motor in advance, and a comparing means for comparing a measured value by the torque measuring means with a set value by the torque setting means. An air pressure selecting unit that controls the pressure adjusting unit so that the measured value falls within the set value; Air semi floating sliding surface static pressure control device for a machine tool, characterized by comprising a weight measuring means for measuring the workpiece weight to determine the weight of the click. 4. A bed, a table for mounting and moving a work, a feed screw for driving the table, a feed servomotor for rotationally driving the feed screw, the bed and the table. In the semi-floating sliding surface of the machine tool, which comprises an air pressure supply path for supplying air pressure to the sliding surface between the pressure adjusting means for selectively supplying the air pressure of the air pressure supply path, and the output of the feed servomotor A torque measuring means for measuring a torque, a torque setting means for setting a threshold value of the output torque of the feed servo motor in advance, and a comparing means for comparing a measured value by the torque measuring means with a set value by the torque setting means. Vibration detecting means for detecting a vibration value of the machine body of the machine tool, and vibration for setting a threshold value of the vibration of the machine body in advance Setting means, comparing means for comparing the vibration detection value of the vibration detecting means with the vibration threshold value of the vibration setting means, and the measurement value of the torque measuring means during fast-forwarding of the table is within the torque setting value. After selecting the air pressure so as to be contained, the air pressure for controlling the pressure adjusting means so as to reduce the air pressure when the vibration detection value by the vibration detecting means at the time of cutting the work becomes equal to or more than the vibration threshold value. A static pressure control device for an air semi-floating sliding surface of a machine tool, characterized by comprising selection means.