This application is based on and claims the benefit of priority from Japanese Patent Application No. 2018-230724, filed on 10 Dec. 2018, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a numerical control device.

Related Art

A machine tool causes a tool to move along a movement path which is decided by a machining program. At this time, if increasing the acceleration of the tool, there are cases where error arises in movement of the tool, and the tool is not made to accurately move on the required movement path. For this reason, as described in Patent Document 1, for example, technology has been known for performing deceleration control to decelerate the tool so that the acceleration of the tool does not exceed a predetermined limit value, at a position at which the movement path curves, for example.

In addition, other than acceleration, it has been known that it is possible to more accurately move the tool by setting limit values for the jerk of the tool, the instant velocity variation for every drive axis, etc. For this reason, among numerical control devices for machine tools, there are those which perform control for decelerating the tool based on a plurality of parameters.

Patent Document 1: Japanese Unexamined Patent Application, Publication No. H11-338530

SUMMARY OF THE INVENTION

In order to shorten the machining time, it is desired to lessen the aforementioned such deceleration of the tool. Therefore, upon machining of mass-produced goods in particular, trying to shorten the machining time, even by a little by lessening the safety factor in the upper limit value of parameters used in deceleration control has been attempted. However, with a change in such a limit value, there is a risk of lowering the machining precision to exceed the permissible range. For this reason, upon changing the limit value of parameters, if it is known for which parameter it is efficient to change the limit value, it will be possible to shorten the machining time relatively easily by suppressing a decline in the machining precision.

The present invention has an object of providing a numerical control device for which shortening of the machining time is easy.

A numerical control device (for example, the numerical control device1described later) according to a first aspect of the present invention is for a machine tool which causes a tool to move along a movement path decided according to a machining program, the numerical control device including: a limit setting storage unit (for example, the limit setting storage unit12described later) in which limit values of a plurality of parameter related to movement of the tool are set; a limit velocity calculation unit (for example, the limit velocity calculation unit25described later) which calculates a plurality of limit velocities which are movement velocities of the tool, which respectively correspond to the limit values of the plurality of parameters at each position of the movement path; a feedrate determination unit (for example, the feedrate determination unit26described later) which defines a minimum value among an ideal velocity of the tool and the plurality of limit velocities at each position on the movement path as a feedrate of the tool at each position on the movement path; and an adjustment effect calculation unit (for example, the adjustment effect calculation unit20described later) which calculates variation in movement time required in order to cause the tool to move an entirety of the movement path at the feedrate, in a case of changing the limit value of the parameter.

According to a second aspect of the present invention, in the numerical control device as described in the first aspect, the plurality of parameters may include acceleration of the tool and jerk of the tool, and the adjustment effect calculation unit may calculate variation in the movement time for every position at which defining the limit velocity as feedrate of the tool, by way of Formula (1) below.

Δ⁢⁢T=2⁢⁢VcR-2⁢⁢VcPA-VcR2-VcP2AV+A⁡(VcR-VcP)JV(1)

In Formula (1), ΔT is variation in the movement time, VcPis the limit velocity corresponding to the limit value prior to change, VcRis the limit velocity corresponding to the limit value after change, V is the ideal velocity, A is the limit value prior to change of acceleration of the tool, and J is the limit value prior to change of jerk of the tool.

According to a third aspect of the present invention, the numerical control device as described in the first and second aspects may further include: a deceleration recording unit for example, the deceleration recording unit17described later) which sums a number of times of the feedrate determination unit defining the limit velocity as the feedrate for each of the parameters; and a count output unit (for example, the count output unit21described later) which displays the number of times summed by the deceleration recording unit for each of the parameters.

With the numerical control device according to the present invention, shortening of the machining time is easy.

