# US 4,597,040 A · Method of retracting and returning a tool from and to a workpiece during the machining of this workpiece by a numerically controlled machining device, and numerically controlled machining device for performing the method

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- Number: US 4,597,040 A
- Document ID: US4597040A
- Status: Granted
- Kind: A
- Application number: 06/527,050
- Filed: 1983-08-29
- Granted: 1986-06-24
- Earliest claimed: 1983-08-29
- Assignees: U.S. Philips Corporation
- Inventors: Aart Buizer
- Web page: https://patentgrep.com/patent/US4597040A

## CPC

- G05B 19/182: {characterised by the machine tool function, e.g. thread cutting, cam making, tool direction control (G05B19/21 - G05B19/40 take precedence)}
- G05B 2219/50109: Soft approach, engage, retract, escape, withdraw path for tool to workpiece
- G05B 2219/50112: Retract tool to a point
- Y10T 82/2502: with program control
- Y10T 408/173: Responsive to work
- Y10T 408/175: to control relative positioning of Tool and work
- G05B: CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS (systems for controlling or regulating non-electric variables G05D; systems for regulating electric or magnetic variables G05F; control devices or systems insofar as characterised by mechanical features only G05G)
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

The control of a tool during a machining operation on a workpiece by means of a numerically controlled device may be interrupted for various reasons. On the occurrence of an interruption the tool is immediately retracted from the workpiece in order to be moved to a retraction position R to avoid marking the workpiece. When the tool is returned to the workpiece, the invention provides a method of moving it so that it converges tangentially towards the workpiece along a curved path, taking up the original tool machining path without marking the workpiece.

## Claims

### Claim 1

In a numerically controlled machining device a method of retracting from and returning a tool respectively to a workpiece during the execution of a program for machining a surface of said workpiece, wherein during said machining the tool being controlled is to follow a tool machining path determined from a calculated tool path and wherein for each reference position on the calculated tool path there is an associated machining position on the tool machining path, said method comprising the steps of:
(a) interrupting the tool progression on the tool machining path along the workpiece during said machining;
(b) storing a first set of data which identify the progress reached in the interrupted machining program and a second set of data which identify the reference position reached at the beginning of the interruption;
(c) determining a tool retraction position which is situated remote from the workpiece;
(d) moving the tool to said tool retraction position;
(e) fetching said second set of data, and determining, on the basis of said reference position reached at the beginning of the interruption, a restart reference position which has its associated restart machining position situated on the tool machining path on a location already reached by the tool before said interruption occurred;
(f) determining a calculated return path which extends between the retraction position and a restart reference position, and wherein at least a part of said calculated return path describes a curved portion which, near the restart reference position, diverges towards a line interconnecting successive reference positions of the calculated tool path, and wherein said calculated return path extends substantially in the same direction as the calculated tool path near the restart reference position;
(g) determining a tool return path on the basis of said calculated return path;
(h) under control of a generated restart command;
(h1) fetching said first set of data;
(h2) returning the tool to the workpiece along said tool return path;
(h3) restarting the interrupted machining program by using the first set of data when said tool has reached the restart machining position.

### Claim 2 (depends on 1)

A method as claimed in claim 1, wherein the curved portion of the calculated return path is shaped as a segment of circle.

### Claim 3 (depends on 2)

A method as claimed in claim 2, wherein the segment of circle path amounts to substantially one quarter of a circle.

### Claim 4 (depends on 1, 2, 3)

A method as claimed in claim 1, 2 or 3, wherein the tool return path and the tool machining path are situated in the same plane.

### Claim 5 (depends on 1, 2, 3)

A method as claimed in claim 1, 2 or 3, wherein the tool is brought into contact with the workpiece near the restart machining position, so that elastic deformation of the tool and/or workpiece occurs near the restart machining position.

### Claim 6

A numerically controlled machining device comprising:
(a) drive means for driving a tool along a tool machining path during the execution of a program for machining a surface of a workpiece, said tool machining path being determined from a calculated tool path wherein for each reference position on the calculated tool path there is an associated machining position of the tool machining path;
(b) interrupting means for interrupting the tool progression on the tool machining path along the workpiece during said machining;
(c) storage means connected to said interrupting means for storing a first set of data which identify the progress reached in the interrupted machining program and for storing a second set of data which identify the reference position reached at the beginning of the interruption;
(d) first means connected to said drive means and being provided for determining a tool retraction position which is situated remote from the workpiece;
(e) second means connected to said storage means and being provided for determining on the basis of said reference position reached at the beginning of the interruption, a restart reference position which has its associated restart machining position situated on the tool machining path on a location already reached by the tool before said interruption occurred;
(f) path determining means connected to said first and said second means being provided for determining a calculated return path which extends between the retraction position and the restart reference position, and wherein at least part of said calculated return path describes a curved portion which, near the restart reference position, diverges towards a line interconnecting successive reference positions of the calculated tool path, and wherein said calculated return path extends substantially in the same direction as the calculated tool path near the restart reference position, said path determining means being further provided for determining a tool return path on the basis of said calculated return path;
(g) control means connected to said drive means, said first and second means and to said path determining means and being provided for controlling the retraction of the tool from the workpiece to the retraction position and for controlling the return of the tool to the workpiece along the tool return path.

### Claim 7 (depends on 6)

A numerically controlled machining device as claimed in claim 6, wherein said numerically controlled machining device being a lathe.