Machine tool monitoring system

• US 4,131,837 A
• Filed: 07/13/1977
• Issued: 12/26/1978
• Est. Priority Date: 11/10/1976
• Status: Expired due to Term

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Whetham, William J.
• Primary Examiner(s): Hohauser, Herman J.
• Application Number:
  US05/815,150
• Time in Patent Office: 531 Days
• Field of Search: 318/571, 318/572, 318/561, 318/566, 235/151.11, 408/11
• US Class Current: 318/571
• CPC Class Codes: G05B 19/4065 Monitoring tool breakage, life or condition
• CPC Class Codes: G05B 19/4163 Adaptive control of feed or cutting velocity without NC B23Q15/12
• CPC Class Codes: G05B 2219/34465 Safety, control of correct operation, abnormal states
• CPC Class Codes: Y10T 408/172 Responsive to Tool

Abstract

During machine tool operation a first set of sensors, referred to as cutter deflection sensors, provides data which is representative of the physical deflection of the cutting tool from a rest position, while a second set of sensors, referred to as position sensors, provides data which is representative of the position of the workpiece mounted on the machine tool relative to a reference or setpoint position. The cutter deflection and workpiece position data are combined to produce a resultant which is representative of the actual position of the cutting tool relative to the workpiece. This resultant is then compared with reference data which is representative of the desired position of the cutting tool relative to the workpiece. The difference between the actual and desired positions is then compared with a preselected tolerance value. The machine tool is then either (1) permitted to continue at its programmed speed, (2) slowed down or (3) stopped, depending on the value of the difference data compared to the tolerance value.

Claims

1. In a numerical control machine tool comprising:

(a) first means for supporting a workpiece relative to a machine reference position such that the position of the workpiece can be ascertained;

(b) second means for supporting a cutting tool means relative to said machine reference position such that the undeflected position of the cutting tool means can be ascertained;

(c) cutting tool means operable to remove material from the workpiece when the machine tool is in operation, said cutting tool means deflecting from a rest position during removal of material from the workpiece;

(d) means for moving said first and second supporting means such that the workpiece and the cutting tool move relative to each other;

(e) means for controlling the movement of the first and second supporting means in accordance with programmed instructions, so as to produce a product of selected configuration and size;

the improvement comprising;

(a) means for determining the position of said first and second supporting means relative to the machine reference position at a given point in time;

(b) means for determining the deflection of said cutting tool means from said rest position during operation of said machine tool at said given point in time;

(c) means for combining the position data and the deflection data in such a manner as to produce a resultant which is representative of the actual position of the cutting tool means relative to the workpiece at said given point in time; and

(d) means responsive to (1) said resultant, (2) reference data representative of the desired position of the cutting tool means relative to the workpiece at said given point in time, and (3) a preestablished tolerance value to alter the operation of said machine tool, when the difference between said resultant and said reference data reaches a predetermined fraction of said tolerance value, in such a manner as to insure that said product will be within the preestablished tolerance.

2. An apparatus of claim 1, wherein said deflection data is in the form of a plurality of deflection signals, each deflection signal being representative of the amount of deflection of said cutting tool means in one axis of deflection thereof, and wherein said position data is in the form of a plurality of position signals, each position signal being representative of the change of position of said machine tool in one axis of movement thereof;

and wherein said apparatus includes a first square and sum means for squaring said deflection signals, summing the squared deflection signals, and taking the square root of the squared and summed deflection signals, a second square and sum means for squaring, summing and square rooting said position signals, and third square and sum means for squaring, summing and square rooting the outputs of said first and second square and sum means, the output of said third square and sum means being said resultant.

3. An apparatus of claim 2, including a plurality of temporary storage means, a plurality of sampling means, and means for controlling said sampling means, and wherein said apparatus includes means applying each deflection signal and each position signal to a temporary storage means, wherein, in operation of said apparatus, said sampling means in response to a programmed instruction samples said deflection signals and said position signals from said temporary storage means at preselected intervals.

4. An apparatus of claim 3, wherein said operation altering means includes means for slowing the feedrate of the machine tool when the difference between said resultant and said reference data is within a first predetermined range relative to said tolerance value and for stopping the operation of said machine tool when said difference is above said first predetermined range.

5. An apparatus of claim 1, wherein said apparatus includes a calculation means, which includes means for calculating the cutting path of said cutting tool means between two known points on said workpiece;

means applying a selected position signal to said calculation means at selected intervals during the actual cutting of said cutting path, means for calculating the theoretical values of the remaining position signals;

means combining said selected position signal and said calculated position signals with desired deflection data into a reference value representative of the desired position of said cutting tool means relative to said workpiece, and means applying said reference value to said operation altering means.

6. A method for monitoring a machine tool operating under the initial control of programmed instructions, comprising the steps of:

(a) initiating machining operation in which a cutting tool removes material from a workpiece under the control of the programmed instructions;

(b) determining the change in position of the machine tool from a reference position at a particular point in time during machining operations, so as to determine the position of the undeflected cutting tool relative to the workpiece;

(c) determining the deflection of the cutting tool from a rest position at the particular point in time;

(d) combining the data obtained as a result of steps (b) and (c) above in such a manner as to produce a resultant which is representative of the actual position of the cutting tool relative to the workpiece at the particular point in time;

(e) calculating the difference between (1) said resultant and (2) a reference value obtained from the programmed instructions which is representative of the desired position of the cutting tool relative to the workpiece;

(f) comparing the difference obtained as a result of step (e) above with a preestablished tolerance value obtained from the programmed instructions;

(g) continuing the control of the machine tool exclusively by the programmed instructions if the difference of step (e) is within a first range relative to the tolerance value;

(h) modifying the programmed instructions to decrease the feedrate of the machine tool if the difference of step (e) is within a second range relative to the tolerance value; and

(i) stopping the machine tool if the difference of step (e) is greater than said second range.

7. The method of claim 6, wherein the position data of step (b) is in the form of a plurality of position signals, each position signal being representative of the change of position of said machine tool in one axis of movement thereof, and wherein the deflection data of step (c) above is in the form of a plurality of deflection signals, each deflection signal being representative of the amount of deflection of said cutting tool in one axis of deflection thereof, and wherein step (d) includes the following steps:

squaring said position signals, summing the squared position signals and taking the square root of the squared and summed position signals;

squaring said deflection signals, summing the squared deflection signals, and taking the square root of the squared and summed deflection signals; and

squaring, summing and taking the square root of the respective squared, summed and square rooted position and deflection signals, the signal produced thereby being the resultant.