Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Reexamination Certificate
1999-08-02
2001-08-21
Dang, Khanh (Department: 2837)
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
C318S569000
Reexamination Certificate
active
06278253
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motor speed controlling method, and more particularly, to a method for controlling speed of a motor for driving an industrial robot.
2. Description of the Related Art
In general, an industrial robot includes mechanical parts for moving a target object on a three-dimensional space or performing a requested job. The robot includes a body which is a central portion for supporting a robot, a manipulator having an arm for moving an end effector into which a tool necessary for a requested job is fitted, to a particular position in a working area, a controller for controlling the manipulator, and a power source for supplying an electric power to the body, the manipulator and the controller. A servo motor is mounted in the arm of the manipulator and the controller controls the servo motor to perform an allocated job.
Generally, a controller includes a main controller, a position controller and a servo driver for driving a servo motor. The main controller produces a speed command profile based on a current position and a user operation command such as a target position input by a user and transfers the produced speed command profile to the position controller. The position controller controls the servo driver based on the received speed command profile and drives the servo motor to move an arm from a certain point to another point. Meanwhile, the position controller receives a current position from an encoder mounted in the servo motor and feedback-controls the position of the arm.
FIGS. 1
a
and
1
a
′ show user command paths according to the conventional art.
FIGS. 1
b
and
1
b
′ show speed command profiles with respect to
FIGS. 1
a
and
1
a
′, respectively according to the conventional art.
FIGS. 1
c
and
1
c
′ show acceleration paths with respect to
FIGS. 1
a
and
1
a
′, respectively, according to the conventional art.
In a conventional robot, the main controller produces a path plan such as a speed trace in which a final target value is planned according to a movement command from a user as shown in
FIGS. 1
a
and
1
a
′. Then, the main controller produces a trajectory plan profile such as a speed command profile in which an actual acceleration and deceleration is performed based on the path plan as shown in
FIGS. 1
b
and
1
b′.
In other words, according to the conventional robot, the main controller produces a path plan to control a servo motor which drives a manipulator, and then produces a trajectory plan profile based on the path plan. As a result, a response to a user command is not fast. Further, even though a trajectory plan profile is given as a continuous value of a smooth curve, a number of points where a differentiation is impossible exist in a jerk such as an acceleration profile as shown in
FIGS. 1
c
and
1
c
′. Since an acceleration change rate is sharp in the vicinity of the differentiation-impossible points, vibration and noise are generated in the motor. The vibration and noise lowers reliability with respect to performance of the robot and gives a shock to mechanical components including a motor, thereby shortening the lifetime of the robot. The vibration and noise is conspicuously severe in a large-scale mechanical apparatus such as an industrial robot which is greatly influenced by the inertia and gravity.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide a motor speed controlling method capable of performing a real-time control, in which a speed command profile and an acceleration profile have a continuous value of a smooth curve, respectively, and the time taken when a changed speed reaches an actual operational speed of a motor is reduced.
To accomplish the above object of the present invention, there is provided a motor speed controlling method for use in a motor speed controlling apparatus including a motor for driving a robot, a position controller for controlling the motor, and a main controller for producing a speed command profile of a smooth curve for controlling the motor based on a robot operational command input by a user and transmitting the produced speed command profile to the position controller, the motor speed controlling method comprising the step of producing a speed command profile having an acceleration profile of a smooth curve within a predetermined robot control interval so that a robot can be controlled on a real-time basis.
Preferably, the speed command profile producing step comprises an operational control preparation step for obtaining a position change amount &Dgr;P, the maximum number of intervals TP
max
, and the number of acceleration intervals TA
max
according to the following expressions:
Formula 1
Δ
P
=
P
g
-
P
c
;
TP
max
=
Δ
P
V
m
;
and
TA
max
=
A
p
wherein P
g
is a target position, P
c
is a current position, V
m
is a maximum speed per unit time and A
p
is an acceleration interval and is a value set by the user robot operational command.
It is preferable that the operational control preparation step comprises the step of obtaining the maximum number of intervals TP
max
, and the number of acceleration intervals TA
max
according to the following expressions:
Formula 2
x
=
TP
max
×
TA
max
;
TA
max
=
x
;
and
TP
max
=
x
TA
max
where the maximum number of intervals TP
max
is smaller than the number of acceleration intervals TA
max
.
It is also preferable that the operational control preparation step comprises the step of obtaining a position change amount &Dgr;P
1
of one interval according to the following expression, using the obtained position change amount &Dgr;P, the obtained maximum number of intervals TP
max
, and the obtained number of acceleration intervals TA
max
, and setting initial values of an initial speed S
i
, a maximum speed S
m
and a final speed S
f
into 0, 1 and 0, respectively:
Formula 3
Δ
P
1
=
Δ
P
TP
max
.
Meanwhile, the speed command profile producing step comprises the step of setting an initial value, TP
c
, of an interval counter which increases by one(1) whenever the speed command profile is produced, to zero, and obtaining values (Aa
0
, Aa
1
, Aa
2
) for calculating a current speed during acceleration, values (Da
0
, Da
1
) for calculating a current speed during deceleration, the number of acceleration intervals T
acc
, the number of deceleration intervals T
dec
, and the number of acceleration and constant speed intervals TP
i
, in order to obtain values of variables necessary for production of the speed command profile, according to the following expressions:
Formula 4
T
acc
=
TA
max
×
&LeftBracketingBar;
S
m
-
S
i
&RightBracketingBar;
;
T
dec
=
TA
max
×
&LeftBracketingBar;
S
m
-
S
f
&RightBracketingBar;
;
TP
i
=
TP
max
-
(
T
acc
×
S
i
+
(
S
m
-
S
f
)
×
T
acc
2
+
(
S
m
-
S
f
)
×
T
dec
2
)
;
Formula 5
Aa
0
=
S
i
;
Aa
1
=
3
T
acc
×
T
acc
×
(
S
m
-
S
i
)
;
Aa
2
=
-
2
T
acc
×
T
acc
×
T
acc
×
(
S
m
-
S
i
)
;
Da
0
=
3
T
dec
×
T
dec
×
(
S
m
-
S
f
)
;
and
Da
1
=
-
2
T
dec
×
T
dec
×
T
dec
×
(
S
m
-
S
f
)
.
It is preferable that when a value of the expression
&LeftBracketingBar;
{
T
acc
×
S
i
+
(
S
m
-
S
i
)
×
T
acc
2
+
(
S
m
-
S
f
)
×
T
dec
}
&RightBracketingBar;
is larger than a predetermined constant, the number of constant speed intervals TP
i
and the maximum speed S
m
are obtained by the following expressions:
Formula 6
TP
i
=
TP
i
+
T
acc
×
S
i
+
(
S
m
-
S
i
)
×
T
acc
2
+
(
S
m
-
S
f
)
×
T
dec
2
-
S
m
VELCOPENSATION
;
and
S
m
=
(
TP
max
-
S
i
×
T
acc
)
T
acc
+
T
dec
+
TP
i
×
2
.
Also, under the above conditions, the current speed value V
c
is calculated to produce a speed command profile, and the obtained current speed V
c
and the current position P
c
are added to update the current position P
c
:
{circle around (1)} whe
Dang Khanh
Larson & Taylor PLC
Samsung Electronics Co,. Ltd.
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