This application claims the benefit of Japanese Patent Application Number 2019-201710 filed on Nov. 6, 2019, the entirety of which is incorporated by reference.

BACKGROUND

1. Technical Field

The disclosure relates to a position measurement method and a position measurement system to measure a position of an object, such as a tool and a workpiece, in a machine of a machine tool and a computer-readable recording medium storing a position measurement program.

2. Related Art

There has been used a method that automatically measures and corrects a tool length and a position of a workpiece for highly accurate machining in a machine tool that performs machining on the workpiece mounted to a table with a tool mounted to a main spindle to be rotated.

As the automatic measurement method of the position of the workpiece, for example, a method that acquires a coordinate at a time point when a contact of a probe, like a touch probe30as illustrated inFIG. 2, contacts a workpiece31or a time point considering a delay is used. In this case, to acquire the coordinate of the workpiece31in a Z-axis direction, a length of the touch probe30at the contact is required.

A general measuring method of the length of the touch probe30at the contact is as follows. A reference tool is mounted to a main spindle2a, and while the Z-axis is manually operated such that the reference tool contacts a reference surface, such as a table3, via a block gauge, a position where a gap between the block gauge and the reference tool becomes approximately 0 is found, and a Z-axis coordinate at the time is recorded. Then, the coordinate of the Z-axis position when the touch probe30is brought into contact with the reference surface is measured. A value found by subtracting the coordinate recorded with the reference tool and a thickness of the block gauge from the coordinate measured with the touch probe30is determined as the length of the touch probe30at the contact. However, manual work is required and it has been difficult to automatically measure the length of the touch probe30at the contact.

Accordingly, the applicant of the present disclosure has disclosed the following method as a method for automatically measuring a length of a touch probe in Japanese unexamined patent application publication No. 2017-193043 (JP-A-2017-193043). A reference block is attached to a tool sensor, such as a touch sensor and a laser sensor, a coordinate of a Z-axis position where a reference tool contacts the reference block is recorded in advance, and a coordinate of the Z-axis position where the reference tool contacts the tool sensor is acquired. From both coordinates, a relative position between the contact position with the tool sensor and the reference block is made known. Then, the contact position of the tool sensor is acquired with the reference tool, the position of the reference block is measured by a position measurement sensor, and a length of the position measurement sensor is corrected for measurement.

When the coordinate of the reference block is acquired at the first time by the method of JP-A-2017-193043, a manual work is required and it has been difficult to be automatically performed in all measurement processes.

Therefore, an object of the disclosure is to provide a position measurement method and a position measurement system of an object in a machine tool that allow automatically performing all measurement processes including a correction and a position measurement program.

SUMMARY

In order to achieve the above-described object, there is provided a position measurement method of an object in a machine tool according to a first aspect of the disclosure that measures a position of the object fixed on a table by a position measurement sensor mountable to a main spindle using the machine tool. The machine tool includes translational axes of three or more axes, the main spindle rotatable with a tool mounted thereon, and the table. The position measurement method includes following steps. The first step is acquiring a sensing position of a distal end of a reference tool using a tool sensor after mounting the reference tool serving as a reference for a length of the tool to the main spindle. The second step is obtaining a length direction correction value of the tool by the tool sensor in a state where the tool is mounted to the main spindle. The third step is rotating the tool such that the tool cuts into a machining block installed on a side of the table to machine a surface and measuring and acquiring a position of the machined surface using the position measurement sensor. The fourth step is calculating a length of the position measurement sensor from the length direction correction value of the tool acquired in the obtaining a length direction correction value and the position of the machined surface acquired in the measuring and acquiring a position of the machined surface. The fifth step is measuring a position of the reference block disposed on a side of the tool sensor using the position measurement sensor and calculating a relative position of the reference block to the sensing position from the sensing position acquired in the acquiring of the sensing position, the position of the reference block, the length of the position measurement sensor calculated in the calculating a length of the position measurement sensor, and the length of the reference tool. The sixth step is acquiring a reference tool position as a distal end position of the reference tool using the tool sensor after mounting the reference tool to the main spindle. The seventh steps is measuring a position of the reference block using the position measurement sensor after mounting the position measurement sensor to the main spindle. The eights step is calculating a length direction correction value of the position measurement sensor from the reference tool position acquired in the acquiring of the reference tool position, the position of the reference block measured in the measuring a position of the reference block, the relative position calculated in the calculating a relative position of the reference block, and the length of the reference tool. The ninth step is measuring the object by the position measurement sensor mounted to the main spindle and correcting a measurement position of the object using the length direction correction value of the position measurement sensor calculated in the calculating a length direction correction value.

Here, “a side of the table” obviously includes a case where the machining block is directly disposed on the table and also includes a case where the machining block is disposed via a tool sensor or the like on the table.

Additionally, “a side of the tool sensor” obviously includes a case where the reference block is directly disposed in the tool sensor and also includes a case where a reference block is separately disposed near the tool sensor.

In the disclosure of a second aspect in the above-described configuration, from the tool sensor position acquisition stage to the relative position calculation stage are performed once. From the reference tool position acquisition stage to the position measurement stage are performed multiple times.

In the disclosure of a third aspect in the above-described configuration, the position measured in the reference block position measurement stage and the position measurement stage by the position measurement sensor is a position of the translational axes when the position measurement sensor senses a contact with the object.

In the disclosure of a fourth aspect in the above-described configuration, the reference block is a reference sphere having a spherical diameter. The position measurement sensor is a contact sensor to the object. The position measurement method further includes a diameter correction value acquisition stage of acquiring a radial direction correction value of the position measurement sensor using the reference sphere before performing the position measurement stage. The position measurement stage corrects the measurement position of the object also using the radial direction correction value acquired in the diameter correction value acquisition stage.

In order to achieve the above-described object, there is provided a position measurement system of an object in a machine tool according to a fifth aspect of the disclosure that measures a position of the object fixed on a table by a position measurement sensor in the machine tool. The machine tool includes translational axes of three or more axes, a main spindle rotatable with a tool mounted thereon, the table, the position measurement sensor mountable to the main spindle, and a control device that controls the translational axes and the main spindle. The position measurement system includes a reference tool, a tool sensor, a reference block, a machining block, a tool sensor position acquisition unit, a tool length correction value acquisition unit, a machined surface position acquisition unit, a position measurement sensor length calculation unit, a relative position calculation unit, a reference tool position acquisition unit, a reference block position measurement unit, a length correction value calculation unit, and a position measurement unit. The reference tool serves as a reference for a length of the tool. The tool sensor is configured to detect a distal end position of the reference tool mounted to the main spindle. The reference block is installed on a side of the tool sensor. The machining block is installed on a side of the table. The tool sensor position acquisition unit is configured to move the reference tool mounted to the main spindle with the translational axes, acquire a sensing position of a distal end of the reference tool using the tool sensor, and store the sensing position. The tool length correction value acquisition unit is configured to move the tool mounted to the main spindle with the translational axes and acquire a length direction correction value of the tool by the tool sensor. The machined surface position acquisition unit is configured to rotate the tool at a given position of the machining block such that the tool cuts into the machining block to machine a surface. The machined surface position acquisition unit is configured to move the position measurement sensor mounted to the main spindle with the translational axes, bring the position measurement sensor into contact with a machined surface to measure, and acquire a position of the machined surface. The position measurement sensor length calculation unit is configured to calculate a length of the position measurement sensor from the length direction correction value of the tool acquired in the tool length correction value acquisition unit and the position of the machined surface acquired in the machined surface position acquisition unit. The relative position calculation unit is configured to measure a position of the reference block using the position measurement sensor mounted to the main spindle and store the position of the reference block. The relative position calculation unit is configured to calculate a relative position of the reference block to the sensing position from the sensing position acquired in the tool sensor position acquisition unit, the position of the reference block, the length of the position measurement sensor calculated in the position measurement sensor length calculation unit, and the length of the reference tool, and store the relative position. The reference tool position acquisition unit is configured to move the reference tool mounted to the main spindle with the translational axes, acquire a reference tool position as the distal end position of the reference tool using the tool sensor, and store the reference tool position. The reference block position measurement unit is configured to measure a position of the reference block by the position measurement sensor mounted to the main spindle and store the position of the reference block. The length correction value calculation unit is configured to calculate a length direction correction value of the position measurement sensor from the reference tool position acquired in the reference tool position acquisition unit, the position of the reference block acquired in the reference block position measurement unit, the relative position acquired in the relative position calculation unit, and the length of the reference tool, and store the length direction correction value. The position measurement unit is configured to measure the object by the position measurement sensor mounted to the main spindle and correct a measurement position of the object using the length direction correction value of the position measurement sensor calculated in the length correction value calculation unit.

In the disclosure of a sixth aspect in the above-described configuration, the machining block is installed to the tool sensor fixed on the table.

In the disclosure of a seventh aspect in the above-described configuration, the position measurement sensor is configured to measure a position of the translational axes when the position measurement sensor senses the object or a position considering a signal delay.

The disclosure of an eighth aspect in the above-described configuration further includes a diameter correction value acquisition unit configured to use the reference block as a reference sphere having a spherical diameter and the position measurement sensor as a contact sensor to the object. The diameter correction value acquisition unit is configured to acquire and store a radial direction correction value of the position measurement sensor. The position measurement unit is configured to correct the measurement position using the length correction value acquired in the length correction value calculation unit and the diameter correction value acquired in the diameter correction value acquisition unit.

In order to achieve the above-described object, there is provided a position measurement program according to a ninth aspect of the disclosure. The position measurement program causes a control device of a machine tool to perform the position measurement method of the object in the machine tool according to any one of the first to the fourth aspects. The machine tool includes translational axes of three or more axes, a main spindle rotatable with a tool mounted thereon, and a table.

With the disclosure, the position of the machined surface which is formed by machining the machining block with the tool is measured by the position measurement sensor. The length of the tool is made known by the tool sensor in advance. As a result, the length of the position measurement sensor, which needs to be made known, can be automatically measured.

Accordingly, the positional relationship between the sensing position by the tool sensor and the reference block is made known from the length of the position measurement sensor and the position of the reference block measured by the position measurement sensor. Thus, after that, by automatically measuring the reference tool by the tool sensor and automatically measuring the reference block by the position measurement sensor, the length of the position measurement sensor, namely, the length direction correction value is automatically measurable.

Additionally, when the position measurement sensor is a contact type, acquiring the correction value in the radial direction together allows further highly accurately measuring the position of the object.

As a result, even when the length of the position measurement sensor changes due to, for example, thermal displacement, all measurement processes including the correction can be automatically performed.

