U.S. patent application number 16/352097 was filed with the patent office on 2020-07-09 for method of load characteristic identification and acceleration adjustment for machine tool.
This patent application is currently assigned to INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE. The applicant listed for this patent is INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE. Invention is credited to Kuo-Hua CHOU, Chien-Chih LIAO, Jheng-Jie LIN, Jen-Ji WANG.
Application Number | 20200218225 16/352097 |
Document ID | / |
Family ID | 69188744 |
Filed Date | 2020-07-09 |
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United States Patent
Application |
20200218225 |
Kind Code |
A1 |
LIN; Jheng-Jie ; et
al. |
July 9, 2020 |
METHOD OF LOAD CHARACTERISTIC IDENTIFICATION AND ACCELERATION
ADJUSTMENT FOR MACHINE TOOL
Abstract
A method of load characteristic identification and acceleration
adjustment for a machine tool is provided. A first acceleration of
a transmission system is set according to the weight of a
workpiece, and the working platform and the workpiece are driven at
the first acceleration. A first elastic deformation of the
transmission system and an amount of first position error of the
transmission system are calculated when transmission system is
moved at the first acceleration. A dynamic error is calculated
according to the first elastic deformation and the first position
error. When the dynamic error is less than or greater than a target
error, a second acceleration is set to the transmission system, and
a second elastic deformation and a second position error are
calculated when the transmission system moves at the second
acceleration unit the dynamic error is converged to the target
error.
Inventors: |
LIN; Jheng-Jie; (Taichung
City, TW) ; CHOU; Kuo-Hua; (Zhubei City, TW) ;
LIAO; Chien-Chih; (Taichung City, TW) ; WANG;
Jen-Ji; (Taichung City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE |
Hsinchu |
|
TW |
|
|
Assignee: |
INDUSTRIAL TECHNOLOGY RESEARCH
INSTITUTE
Hsinchu
TW
|
Family ID: |
69188744 |
Appl. No.: |
16/352097 |
Filed: |
March 13, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G05B 19/406 20130101;
B23Q 15/013 20130101; B23Q 15/12 20130101; G05B 19/404 20130101;
G05B 19/4163 20130101 |
International
Class: |
G05B 19/404 20060101
G05B019/404; G05B 19/406 20060101 G05B019/406; G05B 19/416 20060101
G05B019/416; B23Q 15/013 20060101 B23Q015/013; B23Q 15/12 20060101
B23Q015/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 3, 2019 |
TW |
108100152 |
Claims
1. A method of load characteristic identification and acceleration
adjustment for a machine tool, suitable for applying in the machine
tool, wherein the machine tool comprises a transmission system and
a working platform, the method comprising: setting a first
acceleration of the transmission system according to a weight of a
workpiece, and driving the working platform and the workpiece at
the first acceleration; calculating, according to the weight of the
workpiece, an amount of first elastic deformation of the
transmission system when the transmission system moves at the first
acceleration; calculating, according to a feedback position signal
of the transmission system, an amount of first position error of
the transmission system when the transmission system moves at the
first acceleration; calculating a dynamic error according to the
amount of first elastic deformation and the amount of first
position error, and determining whether the dynamic error is equal
to a target error, and setting a second acceleration to the
transmission system when the dynamic error is less than or greater
than the target error, and calculating an amount of second elastic
deformation and an amount of second position error of the
transmission system when the transmission system moves at the
second acceleration until the dynamic error is converged to the
target error.
2. The method according to claim 1, wherein before setting the
first acceleration, the weight of the workpiece is estimated
according to a current signal of a motor of the transmission
system.
3. The method according to claim 2, wherein a no-load current and a
load current of the motor is calculated according to a difference
between an average current signal in a constant acceleration time
region and an average current signal in a constant velocity time
region.
4. The method according to claim 1, wherein before setting the
first acceleration, the weight of the workpiece is measured by a
scale.
5. The method according to claim 1, wherein a ratio of the second
acceleration to the first acceleration is equal to a ratio of the
target error to the dynamic error.
6. The method according to claim 1, wherein a product of the weight
of the workpiece and the first acceleration is linear with the
amount of elastic deformation.
Description
[0001] This application claims the benefit of Taiwan application
Serial No. 108100152, filed Jan. 3, 2019, the disclosure of which
is incorporated by reference herein in its entirety.
TECHNICAL FIELD
[0002] The disclosure relates in general to an acceleration
adjustment method for a machine tool, and more particularly to a
method of load characteristic identification and acceleration
adjustment for a machine tool.
BACKGROUND
[0003] At present, the main functions of the machine tool include
high-speed and high-precision cutting. With the rapid development
of the controller, adjusting the axial machining parameters can
make the machine tool meet the requirements of high-speed and
high-precision. However, the parameters that the manufacturers of
the machine tool initially adjust in the factory will change in the
actual application due to the weight of the workpiece, which will
influence the speed and precision of the machine tool. In addition,
under the condition of knowing or estimating the weight of the
workpiece, the operator can adjust the parameters of the machine
tool within a certain working range through the trial and error
method. However, the above adjustment method is time-consuming and
needs to be adjusted by the operator manually and repeatedly, which
affects the overall work efficiency.
SUMMARY
[0004] The disclosure is directed to a method of load
characteristic identification and acceleration adjustment for a
machine tool, which can temporarily set an acceleration parameter
according to the weight of the workpiece, and then start the
operation of the machine tool to actually calculate the elastic
deformation and the amount of feedback position error of the
transmission system. After completing multiple feedback controls,
the system can automatically obtain the relationship between the
acceleration parameter and the weight of the workpiece to find an
optimized acceleration parameter.
[0005] According to one embodiment, a method of load characteristic
identification and acceleration adjustment for a machine tool is
provided, which is suitable for applying in the machine tool,
wherein the machine tool includes a transmission system and a
working platform, and the method includes the following steps. A
first acceleration of the transmission system is set according to
the weight of the workpiece, and the working platform and the
workpiece are driven at the first acceleration. An amount of first
elastic deformation of the transmission system is calculated
according to the weight of the workpiece when the transmission
system moves at the first acceleration. An amount of first position
error of the transmission system is calculated according to the
feedback position signal of the transmission system when the
transmission system moves at the first acceleration. A dynamic
error is calculated according to the amount of first elastic
deformation and the amount of first position error, and it is
determined that whether the dynamic error is equal to a target
error, and a second acceleration is set to the transmission system
when the dynamic error is less than or greater than the target
error, and an amount of second elastic deformation and an amount of
second position error of the transmission system are calculated
when the transmission system moves at the second acceleration until
the dynamic error is converged to the target error.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a schematic diagram of an operating system of a
machine tool according to an embodiment of the present
disclosure.
[0007] FIG. 2 is a schematic diagram showing a load characteristic
identification and acceleration adjustment method for a machining
tool according to an embodiment of the present disclosure.
[0008] FIG. 3A is a schematic diagram showing the axial
acceleration and the feed speed of the transmission system of the
machine tool.
[0009] FIG. 3B is a schematic diagram showing estimating the weight
of the workpiece according to the no-load current and the load
current of the machine tool.
[0010] FIG. 4 is a schematic diagram showing the results of weight
estimation.
[0011] FIG. 5 is a schematic diagram showing the percentage of
weight estimation error.
[0012] FIG. 6 is a schematic diagram showing the optimum
acceleration parameters of the machine tool through feedback
control.
[0013] FIG. 7 is a schematic diagram showing the calculation of the
maximum position error based on the feedback position signal.
[0014] FIG. 8 is a schematic diagram showing the relationship
between the weight of the workpiece and the acceleration.
[0015] FIG. 9 is a table showing the relationship between the
weight of the workpiece, the amount of elastic deformation, the
maximum position error, the maximum dynamic error, and the optimum
acceleration.
[0016] In the following detailed description, for purposes of
explanation, numerous specific details are set forth in order to
provide a thorough understanding of the disclosed embodiments. It
will be apparent, however, that one or more embodiments may be
practiced without these specific details. In other instances,
well-known structures and devices are schematically shown in order
to simplify the drawing.
DETAILED DESCRIPTION
[0017] Details are given in the non-limiting embodiments below. It
should be noted that the embodiments are illustrative examples and
are not to be construed as limitations to the claimed scope of the
present disclosure. The same/similar denotations are used to
represent the same/similar components in the description below.
Directional terms such as above, under, left, right, front or back
are used in the following embodiments to indicate the directions of
the accompanying drawings, not for limiting the present
invention.
[0018] According to an embodiment of the present disclosure, a
method of load characteristic identification and acceleration
adjustment for a machine tool is provided, which can be applied in
a computer numerical control (CNC) machine by means of software,
hardware or a combination thereof. The method can be implemented in
the machine, for example, a lathe or a milling machine of
single-axis or multi-axis machining, thereby the axial acceleration
parameters can be adjusted in accordance with the machining
conditions. The settings of the axial acceleration parameters are
related to the weight of the workpiece and the feedback controls of
the motor current, the feed speed, and the position error. The
method in the embodiment can automatically evaluate the weight of
the workpiece and calculate the amount of elastic deformation and
the amount of feedback position error of the transmission system to
find out the relationship between the acceleration parameters and
the weight of the workpiece, so as to adjust the axial acceleration
parameters that best meet the machining conditions.
[0019] The amount of elastic deformation is, for example, the
elastic deformation of the transmission system caused by the load
weight of the workpiece, that is, the elastic deformation of the
screws, nuts, bearings, shaft couplings and the like of the
transmission system when the machine tool is loaded. In general,
the higher the load weight of the workpiece, the higher the amount
of elastic deformation, as shown in FIG. 9.
[0020] Referring to FIG. 1, according to an embodiment of the
present disclosure, when a method of load characteristic
identification and acceleration adjustment is applied in a machine
tool 100, for example, the machine tool 100 may include a weight
estimation module 110, a transmission system 112, a working
platform 114, a deformation calculation module 116, a signal
measurement module 118, and an acceleration parameter setting
module 120. The weight estimation module 110 is used to estimate
the weight 111 of a workpiece. The transmission system 112 is
controlled by a controller 102. The working platform 114 is
disposed on the transmission system 112 for carrying the workpiece
and is driven by the transmission system 112. The deformation
calculation module 116 is used to calculate an amount of elastic
deformation 115 of the transmission system 112. The signal
measurement module 118 is used to measure the electrical signals of
the transmission system 112, such as the current signal, the feed
speed, the axial acceleration, the position signal, and the amount
of position error of the motor. The acceleration parameter setting
module 120 is used to set an optimal acceleration parameter.
[0021] Referring to FIGS. 1 and 2 together, the method of load
characteristic identification and acceleration adjustment applied
in the machine tool of the present disclosure may include the
following steps S11-S17. In step S11, the weight 111 of a workpiece
is estimated. In step S12, a first acceleration of the transmission
system 112 is set according to the weight 111 of the workpiece, and
the work platform 114 and the workpiece are driven at the first
acceleration. In step S13, an amount of first elastic deformation
115 of the transmission system 112 is calculated according to the
weight 111 of the workpiece when the transmission system 112 moves
at the first acceleration. In step S14, an amount of first position
error of the transmission system 112 is calculated according to the
feedback position signal of the transmission system 112 when the
transmission system 112 moves at the first acceleration. In step
S15, a dynamic error is calculated based on the amount of first
elastic deformation and the amount of first position error, and it
is determined whether the dynamic error is equal to a target error.
When the dynamic error is equal to the target error, the current
acceleration is used as an optimization parameter. In step S16,
when the dynamic error is less than or greater than the target
error, the acceleration parameter setting module 120 sets a second
acceleration to the transmission system 112. In step S17, the
transmission system 112 drives the working platform 114 and the
workpiece at the second acceleration, and the deformation
calculation module 116 and the signal measurement module 118
calculate an amount of second elastic deformation and an amount of
second position error of the transmission system 112 when the
transmission system 112 moves at the second acceleration until the
dynamic error is converged to the target error.
[0022] Referring to FIG. 1, in step S11, the weight estimation
module 110 can estimate the weight 111 of the workpiece according
to the current signal of the motor. For example, the transmission
system 112 drives the working platform 114 to move a fixed distance
along the axial direction (for example, from point A to point B)
under a no-load condition. Then, the transmission system 112 drives
the work platform 114 to move a fixed distance along the axial
direction (for example, from point A to point B) in the case of
loading the workpiece. The no-load current T.sub.0 and the load
current T.sub.1 of the motor are respectively calculated when the
transmission system 112 is under no-load or load condition to
establish the relationships between the weight 111 of the workpiece
and the no-load current T.sub.0 and the load current T.sub.1.
[0023] Refer to FIGS. 3A and 3B, a steady current signal in the
constant acceleration time region D1 is defined as a constant
acceleration average current signal Ta, and a steady current signal
in the constant velocity time region D2 is defined as a constant
velocity average current signal Tv. The no-load current T.sub.0 and
the load current T.sub.1 are obtained by using the relationship of
T=Ta-Tv. The no-load current T0 and the load current T1 are taken
into the relationship of
K ( T 1 - T 0 ) = .DELTA. M .times. A .times. P 2 .pi. ,
##EQU00001##
and the weight 111 of the workpiece can be estimated accordingly,
where .DELTA.M is the difference of load weight before and after
loading (i.e., the weight 111 of the workpiece), A is the axial
acceleration, p is the thread pitch, and K is the torque constant.
The relevant content is described as follows.
[0024] When the servo motor of the transmission system 112 drives
the working platform 114 to generate a linear motion, the torque
(.tau.) when the servo motor is accelerated needs to overcome the
inertia (J) of the transmission system 112, the load torque
(T.sub.load) and the friction torque (T.sub.f) required for the
linear motion of the working platform 114, .alpha. is the angular
acceleration, which is expressed by the following equation:
.tau.=J.times..alpha.+T.sub.load+T.sub.f (1)
[0025] The load torque (T.sub.load) in the above equation (1)
indicates that the torque of one rotation of the servo motor is
equivalent to the force (F) to the work platform 114 when the work
platform 114 is pushed to linearly move a thread pitch, and the
force (F) is determined by the weight 111 of the workpiece and the
axial acceleration A of the work platform 114, as indicating in the
following equations (2) and (3):
T.sub.load.times.2.pi.=F.times.pitch (2)
F=.DELTA.M.times.A (3)
[0026] In the above equation (1), when the servo motor drives the
working platform 114 and the workpiece at a constant velocity, the
load torque (T.sub.load) is zero, and the angular acceleration
.alpha. is zero. Therefore, the torque at the constant velocity of
the motor is equal to the friction torque (T.sub.f). That is,
.tau.=T.sub.f.
[0027] In order to accurately obtain the load weight (.DELTA.M), it
is necessary to confirm the stability, reliability and
reproducibility of the electrical signal of motor. Since the
transmission system 112 is subjected to have a position error
(Error) when the servo motor is instantaneously accelerated or
decelerated (jerk), the servo circuit receives the position error
(Error) and compensates for the position error when the servo motor
is accelerated constantly, so as to converge the position error
(Error) to zero. The steady electrical signal is judged by the area
where the position error (Error) is equal to zero. Therefore, in
this embodiment, a steady current signal (i.e., Ta) in the constant
acceleration time region D1 and a steady current signal (i.e., Tv)
in the constant velocity time region D2 can be selected to
calculate the no-load current T.sub.0 and the load current
T.sub.1.
[0028] Since the transmission system 112 is unchanged before and
after loading of the working platform 114 when the servo motor
drives the working platform 114 to generate a linear motion, the
torque at the load current (T.sub.1) subtracts the torque at the
no-load current (T.sub.0) and thus the inertia (J) of the
transmission system 112 and the friction torque (T.sub.f) are
offset in the equation (1). Therefore, the relationship of the
equation (1),
K ( T 1 - T 0 ) = .DELTA. M .times. A .times. P 2 .pi. ,
##EQU00002##
can be obtained, and the weight 111 (.DELTA.M) of the workpiece can
be calculated using the relationship of the equation (1).
[0029] Referring to FIG. 4 and FIG. 5, the weight of the workpiece
is simulated with four loads of standard weight (each 250 kg), and
measure the no-load current (T.sub.0) and the load current
(T.sub.1) on the working platform 114 when the working platform 114
is loaded by 250 kg, 500 kg, 750 kg or 1000 kg according to the
above steps to estimate the weight 111 (.DELTA.M) of the workpiece.
The result of weight estimation and the percentages of weight
estimation error of the workpieces are shown in FIG. 4 and FIG. 5,
when it is estimated by a load block of 250 kg, the estimated
result is 258.5 kg with an error of 3.4%; when it is estimated by a
load block of 500 kg, the estimated result is 474.9 kg; when it is
estimated by a load block of 750 kg, the estimated result is 729.9
kg; and when it is estimated by a load block of 1000 kg, the
estimated result is 973.7 kg, and the estimation error can be
controlled at 2%-10%.
[0030] By using the no-load current (T.sub.0) and the load current
(T.sub.1) of the motor to estimate the weight 111 of the workpiece,
the system can meet the requirements of automated process, reducing
the time and loading of the adjustment of the operator to improve
the overall work efficiency. However, in another embodiment, the
method of estimating the weight 111 of the workpiece is not limited
to the manner described above, and the weight 111 of the workpiece
may also be measured using a scale.
[0031] Referring to FIGS. 2 and 6, in step S12, the controller 102
can set a first acceleration (that is, the current acceleration
113) of the transmission system 112 according to the weight 111 of
the workpiece, and drive the working platform 114 and the workpiece
at the first acceleration. In an embodiment, the controller 102 can
set the first acceleration according to initial machining
parameters of the machine tool 100 or user-customized
parameters.
[0032] Then, in step S13, the deformation calculation module 116
can calculate the amount of first elastic deformation, that is, the
amount of elastic deformation 115 (.delta.), of the transmission
system 112 according to the weight 111 of the workpiece when the
transmission system 112 moves at the first acceleration. In step
S14, the signal measurement module 118 can calculate the amount of
first position error of the transmission system 112, that is, the
largest one of the position errors 117, according to the feedback
position signal of the transmission system 112 when the
transmission system 112 moves at the first acceleration. In step
S15, the acceleration parameter setting module 120 may calculate a
dynamic error, that is, a maximum dynamic error 119, according to
the amount of first elastic deformation 115 and the amount of first
position error, and determine whether the dynamic error is equal to
a target error (E.sub.G).
[0033] Please refer to FIG. 7. The position error 117 will be
affected by the acceleration. When the acceleration changes, the
position error will also increase. When the acceleration is zero,
the position error will converge to zero. In FIG. 7, the maximum
position error is the leftmost position error 117.
[0034] As shown in FIG. 9, the sum of the amount of elastic
deformation 115 (.delta.) and the maximum position error 117 is the
maximum dynamic error 119, and when the maximum dynamic error 119
is equal to the target error (E.sub.G), it indicates that the
current acceleration 113 is the optimum acceleration 122. When the
maximum dynamic error 119 is less than or greater than the target
error (E.sub.G), it indicates that the current acceleration 113 is
not the optimal acceleration 122, and therefore a second
acceleration (A.sub.2) must be calculated based on the maximum
dynamic error 119 (Error), the current acceleration (A.sub.1), and
the target error (E.sub.G). The relationship of the accelerations
A.sub.1 and A.sub.2 is shown as follows:
A 2 = A 1 .times. E G Error . ##EQU00003##
[0035] In step S16, the acceleration parameter setting module 120
sets a second acceleration to the transmission system 112 according
to the above relationship. That is, the ratio of the second
acceleration to the first acceleration is equal to the ratio of the
target error (E.sub.G) to the dynamic error.
[0036] In step S17, the transmission system 112 drives the working
platform 114 and the workpiece at a second acceleration, and the
amount of elastic deformation 115 (.delta.) and the maximum
position error 117 of the transmission system 112 are calculated
when the transmission system 112 moves at the second acceleration
to determine whether the maximum dynamic error 119 is equal to the
target error (E.sub.G). If the maximum dynamic error 119 is still
not equal to the target error (E.sub.G), then the feedback control
is performed to obtain the next stage acceleration 121 again until
the dynamic error is converged to the target error.
[0037] Referring to FIG. 6, which shows a schematic diagram of the
machine tool 100 to find the optimized acceleration parameter
through the feedback control. The deformation calculation module
116 calculates the amount of elastic deformation 115 (.delta.) of
the transmission system 112 based on the weight 111 of the
workpiece. According to Hooke's law and Newton's second law of
motion, the steel of transmission system 112 can be regarded as a
linear elastic material in engineering application, its elastic
coefficient is K, the transmission system 112 is subjected to the
force during the acceleration of the motor, and the force and the
amount of elastic deformation 115 (.delta.) are in a linear
relationship. Since the force is equal to the product of the load
mass of the transmission system 112 and the acceleration, the
relationship between the amount of elastic deformation 115
(.delta.) and the weight of the workpiece 111 (.DELTA.M) is as
follows: .delta.=(.DELTA.M.times.A)/K.
[0038] In FIG. 6, the weight 111 (.DELTA.M) of the workpiece is
inputted to the deformation calculation module 116, and the amount
of elastic deformation 115 (.delta.) of the transmission system 112
at the current acceleration 113 is calculated according to the
above relationship. Then, the acceleration parameter setting module
120 determines whether the current acceleration 113 is the optimal
acceleration 122 according to the difference between the sum of the
amount of elastic deformation 115 (.delta.) and the maximum
position error 117 and the target error. In addition, the upper
controller 103 can transmit the parameters of the next stage
acceleration 121 back to the servo loop of the controller 102, and
the next stage acceleration 121 becomes the current acceleration
113 after the calculation of the current feedback, velocity
feedback and position feedback. This cycle is continued until the
maximum dynamic error 119 is converged to the target error
(EG).
[0039] Referring to FIG. 9, assuming that the target error (EG) is
equal to 12 .mu.m, the acceleration parameter setting module 120
adjusts the optimal acceleration 122 according to the estimation
results of weight 111 of the workpiece (258.5 kg, 474.9 kg, 729.9
kg and 973.7 kg). A table of the relationship between the weight
111 of the workpiece and the optimum acceleration 122 is shown in
FIG. 8. In addition, according to FIG. 9, when the workpieces of
different weights are applied for the target error (EG), the larger
the estimated weight of the workpiece, the larger the amount of
elastic deformation 115 of the transmission system 112, and the
smaller the optimum acceleration 122.
[0040] The machine tool and the method of acceleration control and
adjustment thereof disclosed in the above embodiments of the
present disclosure can temporarily set an acceleration parameter
according to the weight of the workpiece, and then start the
operation of the machine tool to actually calculate the elastic
deformation of the transmission system and the amount of feedback
position error. After completing multiple feedback control, the
system can automatically obtain the relationship between the
acceleration parameter and the weight of the workpiece to find the
optimized acceleration parameter. Therefore, the control method of
the embodiment can be applied to parameter adjustment of various
machine tools and the controller thereof, and achieves the purpose
of automatically adjusting the optimal acceleration parameter.
[0041] It will be apparent to those skilled in the art that various
modifications and variations can be made to the disclosed
embodiments. It is intended that the specification and examples be
considered as exemplary only, with a true scope of the disclosure
being indicated by the following claims and their equivalents.
* * * * *