JPH1128638A - Feed shaft monitoring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically limit feed rate at the time when the thermal expansion of a feed screw exceeds an allowable amount of change by executing a process for failures, if the amount of relative change calculated from the calculated relative positions exceeds an allowable amount of change. SOLUTION: The relationship, calculated by a subtractor 11, between the indirect position of a movable part 17 detected indirectly by a feed screw rotary angle detector 14 and the direct position of the movable part 17 detected directly from the slider 15 of a linear scale 16, varies depending on the amount of thermal expansion of a feed screw 18. In order to detect the change of the relative positions from a reference state, a computing element 10 is used to calculate the difference between an output from the subtractor 11 and that from a reference relative position storage part 12. When the difference output from the computing element 10 exceeds a parameter for the allowable amount of thermal expansion of the feed screw 18, a process for failures, such as stopping the drive of the feed screw, is effected by a part 6 for performing processes in case of failures.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention monitors the influence of thermal expansion generated in a feed screw portion of a numerically controlled machine tool that controls the movement of a movable portion by driving a feed screw to rotate the feed screw portion. The present invention relates to a feed shaft monitoring device for protecting from damage due to stress.

[0002]

2. Description of the Related Art In a machine tool, the feed speed of a feed shaft has been increased in order to meet the demand for shortening the non-cutting time or to improve the performance of a cutting tool. When the feed speed of the feed shaft is increased, the feed screw (such as a ball screw) for transmitting the driving force to the movable portion is also driven to rotate at a high speed, so that thermal expansion occurs and the entire feed screw is extended. It is becoming. The abnormal stress applied to the feed screw as a result of thermal expansion is one of the factors that damages the feed screw.

Conventionally, in order to cope with this abnormal stress,
By using a mechanical structure in which one end of the lead screw is fixed and the other end is not fixed, the elongation of the lead screw is absorbed,
Alternatively, the average continuous feed speed of the feed shaft is limited by machine use.

[0004]

According to the former method described above, since the thermal expansion generated in the feed screw portion is absorbed by the non-fixed side of the feed screw, damage due to abnormal stress in the elongation direction is prevented. Although it can be prevented, there is a drawback that the ball screw nut cannot be protected from damage due to stress due to thermal expansion. According to the latter method, the occurrence of thermal expansion exceeding the allowable amount can be prevented, but it is almost impossible for the operator to always create a feed speed command such that the feed speed of each feed shaft is equal to or lower than the average continuous feed speed. It is possible (the feed speed command is obtained by synthesizing the feed speed commands of the respective feed axes, but since the average continuous feed speed of each feed axis differs depending on the processing shape, such a condition is always satisfied. It is difficult to obtain the feed rate command), and as a result, the absolute value of the feed rate must be limited to be less than the average continuous feed rate and the command must be issued, and the processing efficiency cannot be improved. there were.

SUMMARY OF THE INVENTION It is an object of the present invention to monitor the influence of thermal expansion generated in a feed screw portion, protect the feed screw portion by limiting the feed speed so that the thermal expansion generated in the feed screw is within an allowable amount. It is another object of the present invention to provide a feed axis monitoring device which enables an operator to instruct a feed speed optimal for machining without making an operator aware of thermal expansion of a feed screw portion.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a feed axis monitoring apparatus for a numerically controlled machine tool which controls the position of a movable part by driving a feed screw to rotate. A feed screw rotation angle detecting means for detecting a rotation angle of the screw to calculate an indirect position of the movable part, a movable part position detecting means for detecting a direct position of the movable part, and changing by rotating the feed screw. A relative position relationship calculating unit that calculates a relative position relationship between the indirect position and the direct position; and a parameter storage unit that stores an allowable change amount of the relative position relationship as a parameter. This is achieved by executing an abnormal time process when the relative change amount exceeds the allowable change amount. Further, the object of the present invention is that the movable portion position detecting means comprises a linear scale and a slider for directly detecting the position of the movable portion, and the relative position relationship when the movable portion is at a specific position is referred to. A reference relative positional relationship storage means for storing as a relative positional relationship,
When the relative change calculated from the relative position relation calculated by the relative position relation calculation means and the reference relative position relation stored in the reference relative position relation storage means exceeds the allowable change amount, an abnormal time process is executed. Or the parameters stored in the parameter storage means are made to correspond to at least two stepwise allowable change amounts, and each time the relative change amount exceeds the at least two allowable change amounts, the feed shaft This is effectively achieved by limiting the speed in a step-by-step manner and controlling the drive of the feed shaft to stop when the relative change exceeds the allowable change in the last stage.

[0007]

FIG. 1 is a block diagram showing an embodiment of a feed axis monitoring device according to the present invention. Hereinafter, the operation of the feed axis monitoring device of the present invention will be described with reference to this block diagram.

The program analysis unit 1 analyzes a machining program (not shown). The function generator 2 generates a predetermined function based on a speed command obtained by multiplying the feed speed of the analyzed machining program command by a feed speed override value from the override controller 5 and calculates a position command. And outputs it to the speed control unit 3 every moment. The speed controller 3 calculates a speed command based on the difference between the direct position information from the slider 15 of the linear scale 16 for directly detecting the position of the movable unit 17 and the position command from the function generator 2, 4 is output. On the other hand, the feed screw rotation angle detector 14 detects the rotation angle of the feed screw 18 directly connected to the feed shaft motor 13 and indirectly calculates the position of the movable unit 17 driven via the feed screw 18. .
Movable part 17 output from feed screw rotation angle detector 14
The indirect position information is differentiated by the differentiator 7 and converted into speed, and fed back to the feed shaft drive amplifier 4 as the current speed state. The feed shaft drive amplifier 4 calculates a current command based on the difference between the speed command from the speed control unit 3 and the current speed state from the differentiator 7, and
, The feed screw 18 is driven to move the movable section 17.
Control the position of.

The parameter storage unit 8 stores allowable thermal expansion amount parameters of a plurality of sets of feed screws 18 and a feed speed override value corresponding to each allowable thermal expansion amount as shown in FIG. Is set. The reference relative positional relationship storage unit 12 stores
Relative relationship between the indirect position of the movable portion 17 detected indirectly by the feed screw rotation angle detector 14 and the direct position of the movable portion 17 directly detected from the slider 15 of the linear scale 16 in an initial state (without thermal expansion). Is stored. For example, if the detection unit system and the detection origin of both coincide with each other, the two indicate the exact same position.
Is stored.

When the feed shaft of the numerically controlled machine tool is driven at a high speed, the feed screw 18 generates heat due to friction and causes thermal expansion. Then, the movable portion 17 calculated by the subtractor 11 and indirectly detected by the feed screw rotation angle detector 14 is calculated.
The relative positional relationship between the indirect position and the direct position of the movable portion 17 directly detected from the slider 15 of the linear scale 16 changes according to the amount of thermal expansion of the feed screw 18. In order to detect a change (corresponding to the amount of thermal expansion of the feed screw 18) of the relative positional relationship from the reference state, the subtractor 1
1 and the output from the reference relative positional relationship storage unit 12 are obtained.

The comparator 9 compares the difference output from the arithmetic unit 10 with the allowable thermal expansion amount parameter of the feed screw 18 stored in the parameter storage unit 8 in advance to correspond to the amount of thermal expansion of the feed screw 18. The selected feed speed override value is selected and output to the function generator 2 via the override controller 5. The function generating unit 2 generates a predetermined function based on a speed command obtained by multiplying a feed speed commanded by the machining program analyzed as described above by a feed speed override value from the override control unit 5. And controls the position of the movable part 17. When the difference output from the arithmetic unit 10 exceeds the allowable thermal expansion parameter of the feed screw 18, the abnormal processing unit 6 performs abnormal processing such as stopping the driving of the feed shaft.

When converting the thermal expansion of the feed screw 18 into a unit of extension at a specific position, a correlation between the detected positions may be used. That is, as shown in the graph of FIG. 3, the extension amount ex of the feed screw 18 at the specific position Lc.
0 is the scale position L1 obtained by the method described above.
Can be detected by converting the extension amount ex1 of the feed screw 18 in Equation (1) according to Equation 1.

## EQU1 ## ex0 = ex1 × (Lc / L1)

In the embodiment described above,
Although the linear scale 16 and the slider 15 are used as the movable part position detecting means, the present invention can be similarly implemented using other detecting means. Further, in this embodiment, the relative positional relationship between the indirect position and the direct position of the movable unit 17 in the initial state is stored, and the difference between the stored reference relative positional relationship and the calculated relative positional relationship is obtained. , The relative positional relationship calculated by the relative positional relationship calculating means (subtractor 11 in this embodiment) is directly compared with the allowable variation. Is also good.

[0014]

As described above, in the feed shaft monitoring device of the present invention, the feed speed is automatically limited when the thermal expansion of the feed screw exceeds the allowable change amount. Since the applied abnormal stress is suppressed and the feed screw portion can be prevented from being damaged, the operator can instruct an optimum feed speed for processing, and the processing efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a feed axis monitoring device of the present invention.

FIG. 2 shows a feed screw 18 in the feed axis monitoring device of the present invention.
FIG. 7 is a diagram showing examples of allowable thermal expansion amount parameters and feed speed override values corresponding thereto.

FIG. 3 shows a feed screw 18 in the feed axis monitoring device of the present invention.
FIG. 7 is a diagram showing an example of a correspondence relationship between a rotation angle of a circle and a direct position from a linear scale.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Program analysis part 2 Function generation part 3 Speed control part 4 Feed axis drive amplifier 5 Override control part 6 Abnormality processing part 7 Differentiation part 8 Parameter storage part 9 Comparator 10 Computing unit 11 Subtractor 12 Reference relative position relation storage part 13 Feed shaft motor 14 Feed screw rotation angle detector 15 Slider 16 Linear scale 17 Moving part 18 Feed screw

Claims (4)

[Claims] 1. A feed axis monitoring device for a numerically controlled machine tool that controls the position of a movable part by rotating a feed screw.
A feed screw rotation angle detection unit that detects a rotation angle of the feed screw to calculate an indirect position of the movable unit, a movable unit position detection unit that detects a direct position of the movable unit, and a rotation drive of the feed screw. A relative position relationship calculating unit that calculates a relative position relationship between the indirect position and the direct position that changes, and a parameter storage unit that stores a permissible change amount of the relative position relationship as a parameter, from the calculated relative position relationship. A feed axis monitoring device, wherein an abnormal time process is executed when the calculated relative change exceeds the allowable change. 2. A feed axis monitoring device according to claim 1, wherein said movable portion position detecting means comprises a linear scale and a slider for directly detecting the position of said movable portion. 3. A reference relative positional relationship storing means for storing the relative positional relationship when the movable section is at a specific position as a reference relative positional relationship, wherein the relative position calculated by the relative positional relationship calculating means is provided. 3. The abnormality processing according to claim 1, wherein when the relative change amount obtained from the relationship and the reference relative positional relationship stored in the reference relative positional relationship storage means exceeds the allowable change amount, an abnormal time process is executed. Feed axis monitoring device. 4. A parameter stored in the parameter storage means corresponds to at least two stepwise allowable change amounts, and each time the relative change amount exceeds the at least two allowable change amounts stepwise. 4. The feed shaft monitoring according to claim 1, wherein the speed of the feed shaft is limited in a stepwise manner, and the drive of the feed shaft is stopped when the relative change amount exceeds the allowable change amount of the last stage. apparatus.