WO2009128156A1

WO2009128156A1 - Collision detector and method for detecting collision in processing machine

Info

Publication number: WO2009128156A1
Application number: PCT/JP2008/057496
Authority: WO
Inventors: 隆湯澤; 広一郎服部
Original assignee: 三菱電機株式会社
Priority date: 2008-04-17
Filing date: 2008-04-17
Publication date: 2009-10-22
Also published as: JPWO2009128156A1; JP5168352B2

Abstract

A collision detector includes a drive motor (1), a load current detection means (6) to detect the load current of the drive motor (1), an error detection means (5) to detect error in the drive motor (1) from a position command and a feedback signal from the drive motor (1), and control means (2, 3, 4, 7, 8, 10) to control drive of the drive motor (1). The control means determine whether the drive motor is driven during a processing period or a non-processing period. In case the drive motor is driven during a processing period, the control means detect a collision when the load current detected by the load current detection means (6) increases above a motor load current setting value used as a reference for overload detection of the drive motor (7), and limit the load current to reach at least the motor load current setting value but no more than a given motor current limiting value (4). In case the drive motor is driven during a non-processing period, the control means determine error detected by the error detection means when the load current detected by the load current detection means increases above the motor current limiting value which is set up to be below the load current setting value (8), thereby detecting a collision.

Description

[Name of invention determined by ISA based on Rule 37.2] Collision detection device and collision detection method for processing machines

The present invention relates to a collision load detection device that achieves both collision safety and machining accuracy maintenance by switching a load detection method in an electric discharge machine.

In an apparatus having a movable unit such as a machine tool, when an abnormal load is applied due to a collision at the time of operation or the like, a means for urgently stopping the machine damage is required in order to minimize damage to the machine.
As a general detection means, there is a method of detecting the load amount of the drive motor and detecting a collision at a certain load level or more, but the use state of the machine tool has various states such as during machining and manual feed, Only detection means under certain conditions may cause over-detection, detection delay, etc., depending on the state of use.
When over-detection occurs, the cost increases due to a decrease in system operation rate, and when detection delay occurs, mechanical damage at the time of collision increases.

Therefore, when two types of overload detection levels are provided, a high overload detection level is used for low-speed movement commands, and a low load detection level is automatically switched for high-speed movement commands. (See, for example, Patent Document 1).
Here, by setting the limit value of the motor output level slightly higher than the load detection level for urgently stopping the machine, the time until the machine actually stops after the abnormal load is detected. The impact force during the delay time is minimized.

In addition, by switching the load detection level according to the operation state of the machine tool such as manual operation and automatic operation, fast feed and cutting feed, even if the maximum load such as the non-cutting state is small, abnormal Load detection is realized (see, for example, Patent Document 2).

Also, when the drive current is monitored, depending on the change in the motor drive status, the machining process category such as fast feed or machining feed, machining type division such as rough machining or finishing machining, workpiece material classification, tool type, etc. It is possible to easily detect relatively small abnormalities (tool wear, breakage, machining defects) of the tool during constant-speed feed machining with only a small load change. (See Patent Document 3).

JP-A-10-143216 JP-A-8-323585 Japanese Patent Laid-Open No. 2001-125611

In the conventional collision load detection device, two types of overload detection levels are provided for the servo motor current, the high overload detection level is used for low speed movement commands, and the low load detection level is automatically switched for high speed movement commands. In the case of reducing damage at the time of collision, for example, as shown in FIG. 10, when a low load detection level is set at the time of a high speed movement command, a margin for current fluctuation of the motor current waveform is small, so that the current fluctuation amount increases. May cause false detection of collision.
Then, by causing a detection malfunction, the machine tool or the like controlled by the servo motor is stopped, and the operation rate of an automated system such as a machine tool is reduced.

Also, in order to secure a margin with respect to the current fluctuation component to prevent detection malfunction, the load current set value needs to be set as high as possible. Even when a collision occurs with the motor torque of the time, impact resistance (rigidity) is required so that the parts constituting the machine tool are not damaged.
That is, in the case of a contact processing machine such as a cutting machine, the driving structure assumes a cutting load.
On the other hand, in a non-contact processing machine such as an electric discharge machine, as shown in FIG. 11, there are cases where a lighter structure and ceramic parts for electrical insulation are applied, and impact resistance is higher than that of a contact processing machine. Has a low structure.
In other words, it is practically difficult to achieve both avoidance of damage at the time of impact and avoidance of false detection with respect to a collision during high-speed movement.

In addition, by setting the limit value of the motor output level slightly higher than the load detection level for urgently stopping the machine, the delay from when the abnormal load is detected until the machine actually stops. In order to minimize the impact force during the time, the output level of the motor can only be increased to a level almost equal to the abnormal load detection level.
Generally, in a machine tool that requires high-precision trajectory control, the position control response speed can be improved according to the output level of the motor.
Conversely, when the motor output level is lowered, as shown in FIG. 12, the accuracy of the trajectory of a perfect circle or the like deteriorates, and as a result, the machining accuracy deteriorates.

In addition, as shown in Patent Document 2, the load detection level is switched according to the processing step classification such as manual operation and automatic operation, whether fast feeding or machining feeding, or rough processing or finishing as shown in Patent Document 3. By switching the abnormality detection threshold when monitoring the drive current according to the machine tool operating state, depending on the processing type classification such as machining type, workpiece material classification, tool type, etc., the operating state with a small maximum load (non-cutting state) However, even when an abnormal load can be detected, a margin for current fluctuation is small when a low load detection level is set, and there is a risk of inducing a collision detection error due to an increase in the current fluctuation amount.
That is, it leads to a reduction in the operating rate of an automated system such as a machine tool.

The present invention has been made to solve such a problem. Even in a system that uses a lot of electrically insulating parts such as an electric discharge machine and has a limit in improving the impact resistance of the structure, it is not being processed. An object of the present invention is to obtain a collision load detection device that suppresses mechanical damage due to a collision and that can maintain machining accuracy during machining.

A collision load detection device according to the present invention detects an error of the drive motor from a drive motor, load current detection means for detecting a load current of the drive motor, a position command and a feedback signal from the drive motor. In the collision detection device comprising an error detection means and a control means for controlling the drive of the drive motor, the control means determines whether the drive motor is being driven or not being processed, During machining, a collision is detected when the load current detected by the load current detection means is equal to or greater than a motor load current set value serving as a reference for overload detection of the drive motor, and the load current is The load current detected by the load current detection means is set as the load current when the load is not being processed. When a set motor current limit value or below, and detects the collision by determining the error detected by said error detection means.

According to the present invention, the collision detection mode can be switched between during machining and during non-machining such as during setup, and practical collision detection that achieves both machining accuracy and safety can be realized.

It is a block diagram of the collision load detection apparatus which shows Embodiment 1 of this invention. It is a flowchart of the setting value switching means of a collision load detection apparatus. In Embodiment 1, it is a figure which shows transition of the servomotor electric current during non-processing and during processing. In Embodiment 1, it is a figure which shows the transition method of the servomotor electric current in non-processing, and the setting method of a motor current limiting value. In Embodiment 1, it is a figure which shows the transition method of the servomotor electric current during a process, and the setting method of a motor current limiting value. In Embodiment 2 of this invention, it is a figure which shows the setting method of the load current setting value in process. In Embodiment 2 of this invention, it is a figure which shows the setting method of the load current setting value at the time of setting mask time. In Embodiment 3 of this invention, it is a figure which shows transition of the servomotor electric current during non-processing, and the setting method of a motor current limiting value. In Embodiment 3 of this invention, it is a figure which shows the transition method of the servomotor electric current during non-processing, and the method of setting the allowable error between a movement command-feedback. Diagram explaining the occurrence of false collision detection when the amount of current fluctuation is large Diagram showing a machine tool that uses a low impact resistance member Diagram comparing roundness trajectory accuracy according to motor current limit value

Explanation of symbols

1 drive motor, 2 drive control circuit, 3 motor stop circuit, 4 motor current limit circuit, 5 error detection means between position command and position feedback, 6 comparator, 7 comparator, 8 non-contact sensor, 10 control device, 11 Load current set value setting means, 12 motor current limit value setting means, 13 set value switching means, 14 tolerance setting means.

Embodiment 1 FIG.
FIG. 1 shows the configuration of a collision load detection apparatus according to Embodiment 1 of the present invention.
In FIG. 1, a collision detection apparatus includes a drive motor 1, a drive control circuit 2, a motor stop circuit 3, a motor current limit circuit 4, a position command-position feedback error detection means 5, and the like. The load current detection circuit 6, the

comparators

7 and 8, the control device 10, and the like are included.
Further, the control device 10 includes components of a load current set value setting means 11, a motor current limit value setting means 12, a set value switching means 13, and an allowable error setting means 14. In the collision load detection device, the motor 10 A reference level for drive control is set.

The “load current set value” indicates a reference current value for stopping the motor before it breaks because the structure is damaged when the load current value flowing to the motor exceeds a certain value due to a collision or the like. The “motor current limit value” is a set value for limiting the motor current below a certain current so that the motor output torque is below a certain value. This definition will be used in the future.

As a general operation process, the comparator 7 compares the load current detection result of the drive motor 1 from the load current detection circuit 6 with the load current set value preset by the control device 10, and the detection result If exceeds the set value, the stop circuit 3 stops the motor.
On the other hand, the error amount obtained by the error detection means 5 between the position command and the position feedback and the feedback amount actually driven with respect to the position command is compared with the allowable error set value set by the control device 10 (comparison). If the detected error amount exceeds the set value, the motor is similarly stopped by the stop circuit 3.
Further, the motor is controlled by the drive control circuit 2 so that the motor output torque is always below a certain value, so that the motor current limit circuit 4 always falls below the motor current limit value set by the control device 10. Yes.

In the control device 10, parameters for drive control in the collision load detection device are set by the load current set value setting means 11, the motor current limit value setting means 12, and the position command-position feedback amount allowable error setting means 14. It is remembered.
Specifically, the load current setting value setting means 11, the non-processing mode of operation the load current setting value IK 1 when _the load current setting value IK ₂ at the time of processing operation mode is set, the motor current limit value setting means 12 the non-machining operation mode the motor current limit value iS 1 _during, the motor current limit value iS ₂ at the time of processing operation mode is set.
The load current set value, motor current limit value, and allowable error set value parameters are arbitrarily changed by the set value switching means 13.

FIG. 2 is a flowchart showing the process of the set value switching means 13.
First, the control device analyzes a program such as an NC program to determine the operation mode, and the electric discharge machining device driven by the drive motor takes a predetermined inter-electrode servo between the workpiece and the electrode and performs a pulse. It is determined whether the electric discharge machining is applied with an electric current, or the non-machining such as setup and axis movement is being performed (S1).
If it is determined that in a _non-working, IK 1> load current setting value IK ₁ as the relation of IS _1, defines the motor current limit value IS ₁ (S2), subsequently, it monitors the operation mode (S3), the operation Determine the mode status. If the operation mode has not been changed, the process proceeds to S2, and if it has been changed, the process proceeds to S1.
On the other hand, if it is determined in S1 that machining is in progress, the load current set value IK ₂ and the motor current limit value IS ₂ that satisfy the relationship IK ₂ <IS ₂ are defined (S4), and the operation continues as in S3. The mode is monitored (S5). If the operation mode has not been changed, the process proceeds to S4, and if it has been changed, the process proceeds to S1.
Thereafter, the above process is always executed until the machine is powered off.

Next, how the servo motor current value is controlled every time in this system will be described with reference to FIG.
(1) shows the transition of the motor current value during non-machining.
During non-machining, the set value switching means 13 sets the load current set value IK ₁ > the motor current limit value IS ₁ .
Immediately after the shaft movement based on the drive control circuit 2, the servo motor current of the drive motor 1 increases a current value corresponding to the load inertia at the start, and thereafter, only a motor current value corresponding to the friction load torque is generated in a steady state. Thus, the servo motor current as shown in FIG. 3 is detected by the load current detection circuit 6.
Next, when a collision occurs for some reason, the drive motor 1 increases the servo motor current value in order to counter the collision load. However, the motor current limit circuit 4 determines in advance the motor current limit value setting means 12. and does not increase the current value only motor current up to the limit value iS _1.
That is, since the motor cannot generate a torque exceeding a certain level due to current limitation, the drive shaft cannot advance any further, and an error occurs between the position command and the position feedback, and the error amount reaches a specified value. Thus, the collision is detected and the motor is stopped.
Then, the motor current becomes zero.

(2) shows the transition of the motor current value during machining.
During machining, the set value switching means 13 sets the load current set value IK ₂ <the motor current limit value IS ₂ .
As described above, only the motor current value corresponding to the friction load torque is generated in the steady state after the shaft movement.
Next, when a collision occurs, the drive motor 1 increases the servo motor current value to counter the collision load.
Then, to detect the collision by reaching the load current setting value IK ₂ that is set for the structure to prevent damage, the process proceeds to operation to stop the motor.
However, it is difficult to stop the motor promptly after detection, and a slight delay occurs until the motor is stopped due to communication delay, filter delay, or the like. Therefore, the shaft is driven for the delay time after the collision.
However, even during the detection delay, the motor current limiting circuit 4, only does not increase the current value to the motor current limit value IS ₂ predetermined load below torque corresponding to the current limit value is suppressed.

Next, the effect of this operation will be described.
In the non-machining operation (1), even if a collision occurs, a servo motor current exceeding the motor current limit value IS ₁ does not flow, and a torque exceeding a certain level cannot be generated. Can be suppressed.
Further, as shown in FIG. 4, the level of the collision object motor current-value IS ₁ does not reliably broken (e.g., speed during non-processing of the driving motor which is set in advance, the torque, the load inertia or the like during the axial starting In view of this, by reducing the motor current value to a value near the friction load torque in a steady state, it is possible to further reliably prevent the machine damage. However, lowering the motor current value decreases the responsiveness at the time of driving, and hence the performance of the position trajectory control based on the NC program is reduced. However, since this mode is effective only during non-machining, Deterioration of position trajectory accuracy does not cause a problem in actual use.

In the operation (2) during processing, since the processing is in progress, the position trajectory accuracy needs to be improved as much as possible.
In general, since the position trajectory accuracy can be improved by increasing the response of drive control, it is essential to improve the motor current value to the extent that mechanical resonance does not occur, taking into account the natural frequency of the structure. is there.
For example, as shown in FIG. 5, by setting the motor current limit value IS ₂ for high current, high-precision machining can be realized. The collision detection time has to be determined by the motor current value reaches the load current setting value IK _2.
In this method, there is always a delay until the motor stops after detection. However, in a general electric discharge machine, since the moving speed during actual machining is as low as about 10 mm / min or less, it can be considered almost negligible that the detection delay causes the structure destruction after the collision.

In other words, according to the present embodiment, the machining accuracy is emphasized by switching to a mode that emphasizes machining accuracy during machining, and to a highly safe mode that suppresses machine damage as much as possible during non-machining such as setup. And a practical collision load detection device that achieves both safety and safety.

Embodiment 2. FIG.
In the collision load detection device according to Embodiment 2 of the present invention, in addition to the configuration of FIGS. 1 and 2 described above, the motor is operated during machining within the range of the load current set value IK ₂ shown in FIG. It is characterized by defining a reference current value for stopping.

FIG. 6 defines a settable range of the load current set value IK ₂ during machining that is set in advance in the control device, and the minimum value is a load current that takes into account the machine friction torque and the load inertia at the time of starting the shaft. A value is set, and the maximum value is set as a load current value of + 10% of the load current.

In addition, as shown in FIG. 7, if a fixed mask time is provided only immediately after the start of the axis start and a time to ignore the detection is further provided, an increase in the servo motor current based on the load inertia at the start of the axis is not determined as a collision. because it can be controlled so, it is possible to reduce to a load current value which takes into mechanical friction torque considering the lower limit of the load current setting value IK _2.
As a result, collision detection can be performed quickly, so that it is possible to further reduce the risk of damage to the structure due to a delay until the motor stops after detection.

According to this embodiment, the risk of damage to the structure due to the delay until the motor stops after collision detection is minimized, and at the same time, the maximum machine load torque that occurs during non-collision is detected as collision detection and erroneous detection. The machine down during processing can be suppressed.

Embodiment 3 FIG.
In the collision load detection device according to Embodiment 3 of the present invention, in addition to the configuration of FIGS. 1 and 2 described above, setting of motor current limit value IS ₁ within the range shown in FIG. A range is provided, and the motor current limit value IS ₁ can be set as appropriate.
As in the case of non-machining in the first embodiment, the detection operation at the time of collision detects the collision when the servo motor current is limited by the motor current limit value IS ₁ and the detection error amount is equal to or larger than the set value, and the motor It is characterized by stopping.

FIG. 8 shows the transition of the servo motor current per time. The motor current limit value IS ₁ is equal to or greater than the current value due to the maximum friction torque, and the maximum motor when the structure is not damaged at the time of collision. It shows that the current value is set within the range.
That is, even when the user sets the motor current limit value IS ₁ during non-machining, the settable range is determined, so that a collision failure due to inadvertent setting of the motor current limit value IS ₁ is prevented. be able to.

FIG. 9 shows the transition of the servo motor current per hour in the same manner. However, since the motor cannot generate a torque exceeding a certain level due to current limitation after the collision, the drive shaft cannot advance any further. .
For this reason, an error occurs between the position command and the position feedback, and when the detected error amount is, for example, 3 mm or more as an allowable error setting value, an operation of recognizing a collision and stopping the motor is shown.
Thereby, even if there is a variation in the amount of error between the position command and the position feedback, the risk of erroneous detection of the collision phenomenon can be suppressed.
With the above configuration, damage at the time of collision during non-machining is greatly suppressed, and at the same time, there is no possibility of erroneous detection of collision detection, so machine down during non-machining can be suppressed.

The collision load detection device according to the present invention is a mode in which machine damage at the time of collision is suppressed as much as possible during setup such as during non-machining, and by switching to a mode that emphasizes machining accuracy during machining, low rigidity and low toughness Even in an automatic machine with a structure, practical collision load detection can be realized.

Claims

A drive motor;
Load current detection means for detecting the load current of the drive motor;
Error detection means for detecting an error of the drive motor from a position command and a feedback signal from the drive motor;
Control means for controlling the drive of the drive motor;
In a collision detection device comprising:
The control means determines whether the drive of the drive motor is being processed or not being processed,
During machining, a collision is detected when the load current detected by the load current detection means is equal to or greater than a motor load current set value serving as a reference for overload detection of the drive motor, and the load current is Limit the motor load current to a value that is greater than or equal to the preset motor current limit value,
During non-machining, when the load current detected by the load current detection means becomes equal to or greater than the motor current limit value set below the load current installation value, the error detected by the error detection means is determined. A collision detection device characterized by detecting a collision with
The load current set value indicates a reference current value for determining whether or not the structure provided with the drive motor collides with the workpiece, and the motor current limit value is set so that the motor output torque is less than a certain value. The collision detection device according to claim 1, wherein the collision detection device is a set value for limiting the motor current to a predetermined current or less.
The motor current limit value during machining is set as a parameter of a high current value that is equal to or greater than the torque for controlling the position trajectory of the drive motor, and the motor current limit value during non-machining is the maximum friction of the machine driven by the drive motor. The collision detection device according to claim 1, wherein the collision detection device is set as a low current value that is equal to or greater than the load torque and suppresses the influence at the time of the collision.
The load current setting value during machining can be set as a value that is greater than or equal to the load current value taking into account the maximum frictional load torque of the machine driven by the drive motor and the load inertia at the start of the shaft, and less than or equal to the load current value + 10% Is stored, the collision detection device according to claim 1.
5. The collision detection device according to claim 4, wherein the collision determination based on the load current set value is invalidated during a period from the start of the shaft movement of the drive motor to the occurrence of load inertia.
Stores the range that can be set as the motor current limit value during non-machining as a value equal to or greater than the load current value corresponding to the maximum frictional load torque of the machine driven by the drive motor and less than the maximum load current value at which the structure does not break in the event of a collision The collision detection device according to claim 1, wherein the device is a collision detection device.
7. The collision detection according to claim 6, wherein the error detection means sets the error setting value of the movement command and the feedback signal as 3 mm or more, and is judged as a collision when the error setting value becomes more than the error setting value. apparatus.
In an electric discharge machining apparatus that operates based on an NC program, a case where a drive motor is driven while supplying a predetermined pulse current to a gap between an electrode and a workpiece is a machining motor, and the drive motor is not supplied with a predetermined pulse current. The collision detection device according to claim 1, wherein the collision detection device is determined to be in a non-machining state in which the positioning operation is performed.
9. The collision detection apparatus according to claim 8, wherein the collision detection apparatus is used in an electric discharge machining apparatus that performs electric discharge machining at a low speed of about 10 mm / min or less.
In a collision detection method for detecting a collision of a machine driven by a drive motor,
During machining, a collision is detected when the load current detected by the load current detection means is equal to or greater than a motor load current set value serving as a reference for overload detection of the drive motor, and the load current is Limit the motor load current to a value that is greater than or equal to the preset motor current limit value,
During non-machining, when the load current detected by the load current detection means becomes equal to or greater than the motor current limit value set below the load current installation value, the position command and the feedback signal from the drive motor A collision detection method for detecting a collision by judging an error of a drive motor.
11. The collision detection method according to claim 10, wherein whether the drive motor is driven or not is determined, and the collision detection during the processing or during the non-processing is switched.
The load current set value indicates a reference current value for determining whether or not the structure provided with the drive motor collides with the workpiece, and the motor current limit value is set so that the motor output torque is less than a certain value. 11. The collision detection method according to claim 10, wherein the collision detection method is a set value for limiting the motor current to a certain current or less.
The motor current limit value during machining is set as a parameter of a high current value that is equal to or greater than the torque for controlling the position trajectory of the drive motor, and the motor current limit value during non-machining is the maximum friction of the machine driven by the drive motor. The collision detection method according to claim 10, wherein the collision detection is performed using a value set as a low current value that is equal to or greater than the load torque and suppresses the influence at the time of the collision.
The load current setting value is determined from a range that can be set as a value that is greater than or equal to the load current value taking into account the maximum frictional load torque of the machine driven by the drive motor and the load inertia at the start of the shaft, and less than the load current value + 10%. The collision detection method according to claim 10, wherein collision detection during machining is performed.
15. The collision detection method according to claim 14, wherein the collision determination based on the load current set value is invalidated from the time when the drive motor starts moving to the time when load inertia occurs.
Set the motor current limit value during non-machining from a range that can be set as a value that is equal to or greater than the load current value corresponding to the maximum friction load torque of the machine driven by the drive motor and less than the maximum load current value at which the structure does not break in the event of a collision. The collision detection apparatus according to claim 10, wherein collision detection during non-machining is performed using the non-motor current limit value.
17. The collision detection according to claim 16, wherein the error detection means sets the error setting value of the movement command and the feedback signal as 3 mm or more, and is judged as a collision when the error setting value becomes more than the error setting value. Method.
In an electric discharge machining apparatus that operates based on an NC program, a case where a drive motor is driven while supplying a predetermined pulse current to a gap between an electrode and a workpiece is a machining motor, and the drive motor is not supplied with a predetermined pulse current. The collision detection method according to any one of claims 10 to 17, wherein it is determined that the non-machining operation is performed for positioning.
The collision detection method according to claim 18, wherein the collision detection method is used in electric discharge machining in which electric discharge machining is performed at a low speed of about 10 mm / min or less.