Numerical control unit

• US 20040174130A1
• Filed: 02/19/2004
• Published: 09/09/2004
• Est. Priority Date: 02/21/2003
• Status: Active Grant

• Current Assignee: Fanuc Ltd (Fanuc Corporation)
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Inoue, Michiya, Ishii, Hajime
• Granted Patent: US 6,892,110 B2
• Time in Patent Office: Days
• US Class Current: 318/569
• CPC Class Codes: B23Q 17/09 for indicating or measuring cutting pressure or for determining cutting-tool condition, e.g. cutting ability, load on tool arrangements preventing overload of tools B23Q11/04; devices for indicating failure of drills during boring B23B49/00
• CPC Class Codes: B23Q 17/0961 by measuring power, current or torque of a motor
• CPC Class Codes: G05B 19/4065 Monitoring tool breakage, life or condition
• CPC Class Codes: G05B 2219/50328 As function of motor spindle load, current

Abstract

A numerical control unit having a load monitoring function for monitoring a load on a tool drive source during a machining operation. The numerical control unit includes a load monitoring section for monitoring the load on an electric motor; a wear recognizing section for recognizing the current extent of tool wear; a storing section for storing a plurality of preset limit load values corresponding individually to predetermined various extents of tool wear; a calculating section for calculating the current limit load value corresponding to the current extent of tool wear recognized in the wear recognizing section, based on the plurality of preset limit load values stored in the storing section; and a comparing section for comparing the load on the electric motor, monitored in the load monitoring section, to the current limit load value calculated in the calculating section, and for judging on the abnormality of the load. The wear recognizing section recognizes the current extent of tool wear by using one parameter selected from a group consisting of the number of times of use of a tool, the duration of cutting by a tool, the distance of cutting by a tool and the number of times of execution of machining program. The load monitoring section monitors at least one of maximum value, average value and minimum value of the load in a certain procedure of a machining program.

Claims

1. A numerical control unit for machine tools, comprising:

a load monitoring section for monitoring a load on an electric motor;

a wear recognizing section for recognizing a current extent of tool wear;

a storing section for storing a plurality of preset limit load values corresponding individually to predetermined various extents of tool wear;

a calculating section for calculating a current limit load value corresponding to said current extent of tool wear recognized in said wear recognizing section, based on said plurality of preset limit load values stored in said storing section; and

a comparing section for comparing the load on the electric motor, monitored in said load monitoring section, to said current limit load value calculated in said calculating section, and for judging on an abnormality of said load.

2. A numerical control unit as set forth in claim 1, wherein said wear recognizing section recognizes said current extent of tool wear by using one parameter selected from a group consisting of a number of times of use of a tool, a duration of cutting by a tool, a distance of cutting by a tool and a number of times of execution of machining program.

3. A numerical control unit as set forth in claim 1, wherein said load monitoring section monitors at least one of maximum value, average value and minimum value of said load in a certain procedure of a machining program.

4. A numerical control unit as set forth in claim 3, wherein each of said plurality of preset limit load values stored in said storing section is a preset upper-limit value of said load, and wherein said comparing section compares said maximum value of said load, monitored in said load monitoring section, to said current limit load value calculated in said calculating section based on a plurality of preset upper-limit values.

5. A numerical control unit as set forth in claim 3, wherein each of said plurality of preset limit load values stored in said storing section is a preset upper-limit average value of said load, and wherein said comparing section compares said average value of said load, monitored in said load monitoring section, to said current limit load value calculated in said calculating section based on a plurality of preset upper-limit average values.

6. A numerical control unit as set forth in claim 3, wherein each of said plurality of preset limit load values stored in said storing section is a preset lower-limit average value of said load, and wherein said comparing section compares said average value of said load, monitored in said load monitoring section, to said current limit load value calculated in said calculating section based on a plurality of preset lower-limit average values.

7. A numerical control unit as set forth in claim 3, wherein each of said plurality of preset limit load values stored in said storing section is a preset lower-limit value of said load, and wherein said comparing section compares said minimum value of said load, monitored in said load monitoring section, to said current limit load value calculated in said calculating section based on a plurality of preset lower-limit values.