CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a new U.S. Patent Application that claims benefit of Japanese Patent Application No. 2017-177035, filed Sep. 14, 2017, the disclosure of this application is being incorporated herein by reference in its entirety for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laser machining device, and more particularly relates to a laser machining device that adjusts a focus shift based on a contamination level of an optical system during laser machining.

2. Description of the Related Art

Laser machining devices that perform laser machining of workpieces by irradiating the workpieces with laser light focus laser light on a predetermined focus position with a lens, and irradiate the workpieces with the focused laser light. In such a laser machining device, when the external optical system which guides the laser light from the laser oscillator and focuses it on the workpiece surface is contaminated and absorbs the laser light, the curvature changes and the focus position is moved due to what is known as the thermal lens effect. In addition, depending on how it was contaminated, the transmittance of the external optical system also varies. When a change in the focus position and a change in the transmittance occur, machining defects occur such that it is necessary to check whether the external optical system is contaminated. This is an obstacle to automatic operation.

In order to solve such problems, techniques for detecting contamination of external optical systems by attaching a temperature sensor or a scattered light sensor to the external optical systems are known. In addition, although not during laser machining, JP 2014-117730 A discloses a laser machining device configured to perform, before laser machining, predetermined machining a plurality of times at different focus positions as pre-machining, and setting, based on the relationship between the different focus positions (Fp) and the returning light occurrence period (T) corresponding to each different focus position, the focus position that gives the minimum value (Tm) of the returning light occurrence period as the focus position of the main machining. According to this laser machining device, it is described that setting of the focus position of laser light projected onto a workpiece can be performed stably with a high accuracy without using an independent large-scale device.

JP 2015-199113 A discloses a laser machining device for performing piercing machining, wherein the laser machining device is configured to control a beam diameter variable optical system such that the focusing diameter at the focus point of the laser beam is smaller along with the progression of the piercing machining. According to such a laser machining device, it is described that piercing machining conditions for optimum beam intensity during piercing machining can be selected with respect to the material properties and thickness to be machined.

SUMMARY OF THE INVENTION

The external optical system degrades with time. As a result, loss of laser power occurs at the focus point. As the focus position moves even with minor contamination, this leads to significant degradation in the quality of laser machining. In such cases, it is necessary to promptly replace or clean the optical components. However, when maintenance of optical components is performed after occurrence of machining defects, there is a problem that a large number of defective parts are produced during automatic operation. In contrast, in the method of attaching temperature sensors and scattered light sensors to the external optical system, there are problems in that, as additional equipment is necessary, the device is complicated and the external optical system is heavy, which affects the mechanical performance, and retrofitting cannot be performed. Further, since not all external optical systems are compatible with sensors that can detect contamination, there are times when contamination of the optical system is discovered after machining defects occur.

In addition, in the method of detecting returning light, there is a problem that the returning light cannot be stably detected depending on the type of laser machining actually performed, the material properties of the workpiece, and the surface condition of the workpiece. For example, in a system that performs laser welding, as the surface of a workpiece is melted at the time of welding (time of cleaning, marking) the surface state of the workpiece is not stabilized, and a large amount of noise is included in the returning light. In contrast, in systems that perform laser cutting, returning light can be detected at the time of hole formation machining, but at the time of cutting machining, returning light cannot be detected since the laser light penetrates the workpiece. In particular, in the fly cut used for laser cutting of thin plates, as the laser cutting is performed only by the ON/OFF of laser emission while moving the axis and there is no hole formation machining time when the axis is stopped, returning light cannot be stably detected.

Accordingly, there is demand for a technique for adjusting the focus shift in accordance with the contamination level of the external optical system while stably detecting the returning light during laser machining.

Aspects of the present disclosure provide a laser machining device configured to laser machine a workpiece while correcting a focus shift due to contamination of an optical system, the laser machining device including: a laser oscillator; an external optical system configured to guide laser light from the laser oscillator and focus the laser light on the surface of a workpiece; a returning light measurement unit configured to measure an energy amount of returning light reflected by the workpiece and returning to the laser machining device; a focus shift adjustment unit configured to adjust, based on the energy amount of the returning light during laser machining, a focus shift due to contamination of the external optical system, wherein the focus shift adjustment unit includes: a first focus movement amount calculation section configured to calculate a focus movement amount based on comparison of a first measurement value obtained by averaging a plurality of measurement values measured by the returning light measurement unit within a first period and a second measurement value obtained by averaging a plurality of measurement values measured by the returning light measurement unit within a second period that is temporally later than the first period; and a focus position correction section configured to correct a focus position during laser machining based on the calculated focus movement amount, and the first period is a period shortly after initiation of laser emission when the external optical system is not warmed up or is a period after correcting the focus position, and the second period is a period after passage of a certain time duration when the external optical system is warmed up.

Another aspect of the present disclosure provides a laser machining device configured to laser machine a workpiece while correcting a focus shift due to contamination of an optical system, the laser machining device including: a laser oscillator; an external optical system configured to guide laser light from the laser oscillator and focus the laser light on the surface of a workpiece; a returning light measurement unit configured to measure an energy amount of returning light reflected by the workpiece and returning to the laser machining device; a focus shift adjustment unit configured to adjust, based on the energy amount of the returning light during laser machining, a focus shift due to contamination of the external optical system, wherein the focus shift adjustment unit includes: a first focus movement amount calculation section configured to calculate a focus movement amount based on comparison of a first measurement value measured by the returning light measurement unit at a time of a first hole formation machining and a second measurement value measured by the returning light measurement unit at a time of a second hole formation machining that is temporally later than the time of the first hole formation machining; and a focus position correction section configured to correct a focus position during laser machining based on the calculated focus movement amount, and the time of the first hole formation machining is a point in time shortly after initiation of laser emission when the external optical system is not warmed up or is a point in time after correcting the focus position, and the time of the second hole formation machining is a point in time after passage of a certain time duration when the external optical system is warmed up.

Another aspect of the present disclosure provides a laser machining device configured to laser machine a workpiece while correcting a focus shift due to contamination of an optical system, the laser machining device including: a laser oscillator; an external optical system configured to guide laser light from the laser oscillator and focus the laser light on the surface of a workpiece; a returning light measurement unit configured to measure an energy amount of returning light reflected by the workpiece and returning to the laser machining device; a focus shift adjustment unit configured to adjust, based on the energy amount of the returning light during laser machining, a focus shift due to contamination of the external optical system, wherein the focus shift adjustment unit includes: an output command section configured to issue, with respect to the laser oscillator, a command to emit laser light at a predetermined output or a command to not emit laser light, a focus movement amount calculation section configured to calculate a focus movement amount based on comparison of a first measurement value obtained by averaging peak values measured by the returning light measurement unit when changing from the command not to emit laser light to the command to emit laser light within a first period and a second measurement value obtained by averaging peak values measured by the returning light measurement unit when changing from the command not to emit laser light to the command to emit laser light within a second period that is temporally later than the first period; and a focus position correction section configured to correct a focus position during laser machining based on the calculated focus movement amount, and the first period is a period shortly after initiation of laser emission when the external optical system is not warmed up or is a period after correcting the focus position, and the second period is a period after passage of a certain time duration when the external optical system is warmed up.

A further aspect of the present disclosure provides a laser machining device configured to laser machine a workpiece while correcting a focus shift due to contamination of an optical system, the laser machining device including: a laser oscillator; an external optical system configured to guide laser light from the laser oscillator and focus the laser light on the surface of a workpiece; a returning light measurement unit configured to measure an energy amount of returning light reflected by the workpiece and returning to the laser machining device; a focus shift adjustment unit configured to adjust, based on the energy amount of the returning light during laser machining, a focus shift due to contamination of the external optical system, wherein the focus shift adjustment unit includes: a change amount calculation section configured to calculate a change amount per unit time of the energy amount of the returning light measured by the returning light measurement unit, a focus movement amount calculation section configured to calculate a focus movement amount based on comparison of a first measurement value obtained by averaging peak values measured by the returning light measurement unit when the change amount per unit time calculated by the change amount calculation section within a first period is greater than or equal to a certain value and a second measurement value obtained by averaging peak values measured by the returning light measurement unit when the change amount per unit time calculated by the change amount calculation section within a second period that is temporally later than the first period is equal to or greater than a certain value; and a focus position correction section configured to correct a focus position during laser machining based on the calculated focus movement amount, and the first period is a period shortly after initiation of laser emission when the external optical system is not warmed up or is a period after correcting the focus position, and the second period is a period after passage of a certain time duration when the external optical system is warmed up.

