Laser processing device having gap control function and controller thereof

A controller for a laser processing device for processing an object to be processed by condensing light from a processing nozzle, irradiating the light to the object, and moving the processing nozzle and/or the object relative to each other based on a processing program, the controller comprising:

• a deceleration start distance calculating part which calculates a deceleration start distance corresponding to a distance between the processing nozzle and the object when deceleration of relative movement between the processing nozzle and the object is started;
• a first velocity command generating part which generates a first velocity command value based on the deceleration start distance, a predetermined maximum approach velocity and a predetermined deceleration rate;
• a second velocity command generating part which generates a second velocity command value based on a target value of a gap between the processing nozzle and the object and a feedback value from a gap sensor for detecting the gap;
• and
• a velocity command switching part which switches a velocity command for the relative movement between the first and second velocity command values,
• wherein the deceleration start distance calculating part obtains the first velocity command value after the distance between the processing nozzle and the object is equal to the deceleration start distance and the second velocity command value, and calculates the deceleration start distance so that an absolute value of a difference between the first and second velocity command values at a first time point is equal to or smaller than 10% of an absolute value of the first velocity command value at the first time point, and so that an absolute value of a difference between first order differential values of the first and second velocity command values at the first time point is equal to or smaller than 10% of an absolute value of the first order differential value of the first velocity command value at the first time point.