CN110045681B - External compensation method for numerical control machine tool position-related errors based on position prediction - Google Patents
External compensation method for numerical control machine tool position-related errors based on position prediction Download PDFInfo
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- CN110045681B CN110045681B CN201910182745.7A CN201910182745A CN110045681B CN 110045681 B CN110045681 B CN 110045681B CN 201910182745 A CN201910182745 A CN 201910182745A CN 110045681 B CN110045681 B CN 110045681B
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- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B19/00—Programme-control systems
- G05B19/02—Programme-control systems electric
- G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form
- G05B19/404—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by control arrangements for compensation, e.g. for backlash, overshoot, tool offset, tool wear, temperature, machine construction errors, load, inertia
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- G—PHYSICS
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- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B2219/00—Program-control systems
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- G05B2219/35—Nc in input of data, input till input file format
- G05B2219/35408—Calculate new position data from actual data to compensate for contour error
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Abstract
The invention discloses an external compensation method for position-related errors of a numerical control machine tool based on position prediction, which comprises the steps of measuring the communication delay of an external error compensation controller and a numerical control system through off-line measurement, calculating to obtain position lead by combining with the real-time feeding rate of the numerical control machine tool, superposing with a real-time position, predicting to obtain position data, calculating compensation amount by using the predicted position data, inputting the compensation amount into the numerical control system, and finishing the output of the compensation amount to the tip end of a processing cutter by the numerical control system through an origin offset method. The invention solves the problem of time lag of position information for calculating compensation amount due to the communication between the external compensation controller and the numerical control system, and improves the accuracy of external error compensation.
Description
Technical Field
The invention belongs to the technical field of error compensation of numerical control machines, and particularly relates to an external compensation method for numerical control machine position-related errors based on position prediction.
Background
The numerical control machine tool is one of important basic equipment in the current manufacturing industry, the precision is a key index of a high-end numerical control machine tool, the precision is generally represented by a machining error, and the machining error directly determines the machining quality of a product. Errors whose magnitude is related to position in the machine tool are referred to as position-dependent errors. The error compensation is an important technical means for eliminating errors, and means that on the basis of allowing errors to be generated, a compensation quantity which is equal to the original error in magnitude and opposite to the original error in direction is artificially manufactured and is superposed to the actual processing movement of a machine tool. The method mainly comprises the steps of obtaining an error distribution rule through error measurement, establishing an error prediction model, predicting to obtain a compensation quantity, and superposing the compensation quantity to the actual motion of the machine tool. The error compensation technology does not depend on the precision of the machine tool, so that the production cost and the maintenance cost of the machine tool are reduced; meanwhile, the compensation amount can be adjusted at any time conveniently according to the change of the working condition, the error eliminating effect is good, and the real-time performance is strong.
Part of commercial numerical control systems open compensation function interfaces for users, and by developing an external error compensation controller, a more accurate compensation algorithm can be adopted to predict more accurate compensation amount, and the more accurate compensation amount is input into the numerical control system through the compensation function interfaces.
For the position-related error, real-time position information needs to be acquired from the numerical control system based on the communication mode of the numerical control system and is used as an error model input. However, the communication between the external compensator and the numerical control system needs to depend on media, such as ethernet cables, etc., which can cause the problem of communication delay, the acquired position data has the problem of time lag, and the real-time performance is poor, so that the compensation quantity obtained by model calculation has low precision and does not meet the real-time performance requirement of online compensation.
Therefore, to compensate the position-related error based on the external compensation method, and to achieve a good compensation effect, the problem of time lag of position data caused by communication delay between the external compensation controller and the numerical control system must be solved.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides an external compensation method for numerical control machine tool position-related errors based on position prediction, which can solve the problem of position data time lag between an external compensation controller and a numerical control system caused by communication delay.
The technical scheme of the invention is as follows:
an external compensation method for numerical control machine tool position-related errors based on position prediction comprises the following steps:
(1) establishing communication connection between an external error compensation controller and a numerical control machine tool, wherein the external error compensation controller is provided with a position-related error prediction model which is solidified off line in advance;
(2) measuring the communication delay between the external error compensation controller and the numerical control machine tool off line, and writing the measured communication delay into the external error compensation controller;
(3) after the online compensation is started, the external error compensation controller acquires current position data and a current actual feeding rate, calculates position lead by combining communication delay and the current actual feeding rate, obtains pre-judgment position data by overlapping the position lead with the current position data, inputs the position of the pre-judgment data into a position-related error prediction model, and calculates to obtain an error amount;
(4) the external error compensation controller sends the error amount to the PLC, and the PCL writes the error amount into an original point offset register of the numerical control system through an internal CNC-PLC communication bus;
(5) the numerical control system starts an original point offset function, and the numerical control system outputs a theoretical code instruction superposed with an original point offset value according to an error value in an original point offset register, automatically drives a lead screw, drives a workbench to move in the opposite direction of the error value, and realizes error compensation.
In the step (1), the communication connection comprises an Ethernet or IO bus connection, and if the numerical control machine tool is externally connected with a measuring system, the measuring system is connected with an external error compensation controller.
In the step (2), if the external error compensation controller acquires position data and real-time feed rate from the numerical control machine based on communication connection, the communication delay comprises two-way communication time for acquiring data and writing error;
if the external error compensator directly obtains the position data and the real-time feeding rate from a measuring system externally connected with the machine tool, the communication delay only comprises one-way communication time for writing the error amount.
The communication delay measuring method comprises the following steps:
(2-1) the external error compensation controller records the initial time T1;
(2-2) the external error compensation controller executes a program for writing data into a numerical control system register of the numerical control machine tool and sets an active delay Ts;
(2-3) the external error compensation controller executes a program for reading data from a numerical control system register of the numerical control machine tool and records the current time T2;
(2-4) calculating a unit communication time by using the formula T ═ T2-T1-Ts)/4;
(2-5) if the external error compensation controller obtains position data and a real-time feed rate from the machine tool based on communication connection, the communication delay comprises four unit communication times; if the external error compensator directly obtains the position data and the real-time feed rate from the measurement system, the communication delay comprises two unit communication times.
Preferably, in the step (2-2), the active delay Ts is set to be greater than 500ms, and the active delay Ts is set to be beneficial to reducing calculation errors.
In the step (4), the external error compensation controller sends the error amount to the PLC through the ethernet or IO bus.
According to the invention, by measuring the communication delay between the external compensation controller and the numerical control system in an off-line manner, the time lag generated by the communication between the external compensation controller and the numerical control system when the position information for calculating the compensation quantity is calculated is solved, the real-time performance of error quantity calculation is improved, and the error compensation precision of the commercial numerical control system is improved.
Drawings
FIG. 1 is a schematic diagram of an external compensation method for errors related to the position of a numerically-controlled machine tool based on position prediction according to the present invention;
FIG. 2 is a schematic flow chart illustrating an external compensation method for position-related errors of a numerically controlled machine tool based on position prediction according to an embodiment of the present invention;
fig. 3 is a schematic diagram illustrating a method for measuring a communication delay based on an ethernet communication compensation error according to an embodiment of the present invention.
Detailed Description
The invention will be described in further detail below with reference to the drawings and examples, which are intended to facilitate the understanding of the invention without limiting it in any way.
The invention uses an external error compensation controller based on an original point offset compensation functional interface provided by a numerical control system, predicts real-time position data by combining communication delay time, calculates error compensation amount and implements error compensation. The principle is as shown in fig. 1, and it is assumed that the compensation controller calculates the compensation amount C1 at time T1 and starts outputting, based on the position data P1 at time T1; because of the delay T, the compensation is performed at time T2, and the machine position P2 is different from P1, the error compensation amount is necessarily deviated. Now, the compensation response time T is measured off line, the position data P of the machine tool movement in the delay time T is obtained by multiplying the compensation response time T by combining the actual feed rate F of the machine tool, the position data P is superposed with the real-time position P1, the machine tool position P2 when the compensation implementation time T2 is predicted is input into an error model, and the error amount is obtained through calculation.
As shown in fig. 2, an external compensation method for position-related errors of a numerically-controlled machine tool based on position prediction includes the following steps:
step 1, according to a data interface of a numerical control system, establishing communication connection between an external error compensation controller and a numerical control machine tool based on an Ethernet cable or an I/O bus. If an additional measuring system is arranged, the external measuring system is accessed to an external compensation controller;
and 2, obtaining the communication time for the external compensation controller to obtain the machine tool position data and the real-time feeding rate of the machine tool from the numerical control system and write error amount into the numerical control system through off-line measurement. An example of measuring communication time is described with an example of establishing a communication connection between an external compensation controller and a FANUC numerical control system based on an ethernet cable, as shown in fig. 3.
The compiling execution time t1 and t3 of the internal instruction of the external compensation controller is not considered, the reading and writing time Tc inside the PMC is not considered, and the time delay Ts is set between calling reading and writing functions, so that the calculation error is reduced. And supposing that the communication time t2 includes that after the register writing instruction is sent out, the data can reach the numerical control system through one unit of communication time, and then one handle is returned to the compensation controller through one unit of communication time, namely, the total time is two units of communication time; similarly, it is assumed that the communication time t4 also includes two unit communication times. The experimental procedure was as follows:
a) after the offline measurement starts, the time T1 in ms is obtained by calling the function clock () in windows.
b) A function is executed that specifies a register write to the numerical control system.
c) And (4) delaying by using a sleep () function, wherein the delay time is Ts and is set to be 1000ms in the experiment.
d) And executing a function for reading the numerical control system specified register value.
e) Call again function clock () in windows. h resulting in time T2 in ms.
f) And one unit communication time T is (T2-T1-Ts)/4.
After measuring to obtain a unit delay T, defining the delay T as quadruple T aiming at the condition of obtaining position data from the machine tool; for the case of acquiring position data from a measurement system, the delay T is defined as twice T. And writing the delay t into an external compensation controller.
And 3, after the online compensation is started, the external compensation controller acquires current position data P1 and a current feed rate F, multiplies the current position data by combining the actual feed rate F of the machine tool to obtain position data P of the movement of the machine tool within the delay time T, superposes the position data P with a real-time position P1, predicts the position P2 of the machine tool at the compensation implementation time T2, inputs the position data P into a position-related error prediction model which is solidified in advance, calculates to obtain an error amount, and transmits the error amount based on the Ethernet.
Step 4, the PLC obtains an error amount based on the Ethernet interface and writes the error amount into an original point offset register of the numerical control system through an internal CNC-PLC communication bus;
and 5, starting an original point offset function by the numerical control system, superposing a theoretical code instruction on the original point offset value and outputting the superposed original point offset value according to the error value in the original point offset register in the numerical control system, automatically driving a lead screw, driving the workbench to move in the opposite direction of the error value, and realizing error compensation implementation.
The embodiments described above are intended to illustrate the technical solutions and advantages of the present invention, and it should be understood that the above-mentioned embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention, and any modifications, additions and equivalents made within the scope of the principles of the present invention should be included in the scope of the present invention.
Claims (6)
1. An external compensation method for numerical control machine tool position-related errors based on position prediction is characterized by comprising the following steps:
(1) establishing communication connection between an external error compensation controller and a numerical control machine tool, wherein the external error compensation controller is provided with a position-related error prediction model which is solidified off line in advance;
(2) measuring the communication delay between the external error compensation controller and the numerical control machine tool off line, and writing the measured communication delay into the external error compensation controller;
(3) after the online compensation is started, the external error compensation controller acquires current position data and a current actual feeding rate, calculates position lead by combining communication delay and the current actual feeding rate, obtains pre-judgment position data by overlapping the position lead with the current position data, inputs the position of the pre-judgment data into a position-related error prediction model, and calculates to obtain an error amount;
(4) the external error compensation controller sends the error amount to the PLC, and the PLC writes the error amount into an original point offset register of the numerical control system through an internal CNC-PLC communication bus;
(5) the numerical control system starts an original point offset function, the numerical control system outputs a theoretical code instruction superposed with an original point offset value according to an error value in an original point offset register, a lead screw is automatically driven, a workbench is driven to move in the opposite direction of the error value, and error compensation is achieved.
2. The external compensation method for errors related to positions of numerically-controlled machine tools according to claim 1, wherein in step (1), the communication connection comprises an ethernet or IO bus connection, and if the numerically-controlled machine tools are externally connected with a measurement system, the measurement system is connected with an external error compensation controller.
3. The external compensation method for errors related to positions of numerically controlled machine tools based on position prediction as claimed in claim 1, wherein in the step (2), if the external error compensation controller obtains the position data and the real-time feeding rate from the numerically controlled machine tools based on the communication connection, the communication delay includes a two-way communication time for obtaining the data and writing the error amount;
if the external error compensator directly obtains the position data and the real-time feeding rate from a measuring system externally connected with the machine tool, the communication delay only comprises one-way communication time for writing the error amount.
4. The external compensation method for numerical control machine position related errors based on position prediction according to claim 3, wherein in the step (2), the communication delay is measured by:
(2-1) the external error compensation controller records the initial time T1;
(2-2) the external error compensation controller executes a program for writing data into a numerical control system register of the numerical control machine tool and sets an active delay Ts;
(2-3) the external error compensation controller executes a program for reading data from a numerical control system register of the numerical control machine tool and records the current time T2;
(2-4) calculating a unit communication time by using the formula T ═ T2-T1-Ts)/4;
(2-5) if the external error compensation controller obtains position data and a real-time feed rate from the machine tool based on communication connection, the communication delay comprises four unit communication times; if the external error compensator directly obtains the position data and the real-time feed rate from the measurement system, the communication delay comprises two unit communication times.
5. The method for externally compensating position-related errors of a numerically-controlled machine tool according to claim 4, wherein in the step (2-2), the active delay Ts is set to be greater than 500 ms.
6. The external compensation method for numerical control machine position-related errors based on position prediction according to claim 1, wherein in the step (4), the external error compensation controller sends the error amount to the PLC by means of ethernet or IO bus.
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