Information
-
Patent Grant
-
6467582
-
Patent Number
6,467,582
-
Date Filed
Monday, March 20, 200024 years ago
-
Date Issued
Tuesday, October 22, 200222 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Lillis; Eileen D.
- Tran; Thuy V.
Agents
- Armstrong, Westerman & Hattori, LLP
-
CPC
-
US Classifications
Field of Search
US
- 414 277
- 414 281
- 414 282
- 104 121
- 187 406
- 187 244
- 187 347
-
International Classifications
-
-
Disclaimer
Terminal disclaimer
Abstract
An upper cart 12 and a lower cart 2 have running motors 4, 14, respectively, for controlling these carts in a manner overlapping each other on a vertical line. A mast 18 is formed into a truss structure, and an elevating platform 20 has a slide fork a load on which is supported on a shelf support of a rack. The present invention provides a light stacker crane operating at a high speed.
Description
FIELD OF THE INVENTION
The present invention relates to improvements of a stacker crane.
BACKGROUND OF THE INVENTION
In an automatic warehouse, a stacker crane is used as a transfer device wherein a cylindrical mast is provided on a lower cart so that an elevating platform can be elevated and lowered along the mast. Since the mast is rigid and is, for example, 30 m in height, the mast is thus very heavy. Correspondingly, the stacker crane is heavy and operates at a low speed.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a light stacker crane operating at a high speed.
It is an additional object of the present invention to reduce the weight of the mast to facilitate an increase in speed of the stacker crane.
It is an additional object of the present invention to reduce an unbalanced load on the mast to further reduce the weight.
It is an additional object of the present invention to allow the stacker crane to be smoothly driven at a high speed in order to improve the transfer capability of the stacker crane.
It is an additional object of the present invention to provide a specific mechanism for transmitting thrust to the mast.
It is an additional object of the invention to absorb vibration in the mast.
A stacker crane according to the present invention is characterized by having an upper cart provided at the top of a mast, a running motor and running wheels provided in each of a lower cart and the upper cart, and control means for controlling at least one of the running motors so that the upper and lower carts overlap each other on a vertical line.
Preferably, the upper and lower carts each have a position-recognizing means such as a laser range finder, and the control means is configured so as to allow the upper and lower carts to overlap each other on a vertical line by controlling the running motor for the cart running ahead, in a manner synchronizing with the running motor for the cart running behind.
In addition, preferably, the mast of the stacker crane is formed into a truss structure comprising a plurality of columnar members.
Further, preferably, the mast is slidably connected to at least one of the upper and lower carts.
In addition, preferably, the mast is elastically connected to at least one of the carts.
Further, preferably, the mast is connected to at least one of the carts via dampers.
According to the present invention, the lower cart is provided at the bottom of the mast, while the upper cart is provided at the top of the mast. The lower and upper carts each have the running motor and the running wheels so as to run by means of these components. The running motors are controlled so that the upper and lower carts overlap each other on a vertical line. When the upper and lower carts overlap each other on a vertical line, the mast is subjected to no force acting in a horizontal direction of the stacker crane, so that the weight of the mast can be reduced. Then, the upper and lower carts are driven relative to this mast with a reduced weight, thereby increasing the speed of the stacker crane.
According to the present invention, the upper and lower carts are allowed to overlap each other on a vertical line by controlling the running motor for the cart running ahead, in a manner synchronizing with the running motor for the cart running behind. As a result, the upper and lower carts can be allowed to constantly overlap each other on a vertical line.
According to the present invention, the mast is formed into a truss structure, thereby reducing the weight of the mast and further increasing the speed of the stacker crane.
According to the present invention, since the mast is slidably connected to at least one of the upper and lower carts, control errors between the upper and lower carts are absorbed by sliding of the mast to prevent an excess force from being applied to a connection between each of the carts and the mast. The cart to which the mast is slidably connected applies a thrust to the mast depending on the amount of sliding. If, for example, the amount of sliding is zero, almost no force is applied to the mast to allow this cart to run by means of a thrust from the other cart. Consequently, the stacker crane can be run at a high speed, and the connection between the mast and the cart is prevented from being subjected to an excess force.
According to the present invention, since the mast is elastically connected to the one of the carts, an elastic force can be applied to the mast as a thrust, depending on the amount of sliding.
According to the present invention, the dampers serve to prevent the mast from vibrating and in particular to promptly end vibration of the mast when the stacker crane is stopped, thereby reducing the time required before a loading operation can be started.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a side view of a stacker crane according to an embodiment of the present invention.
FIG. 2
shows how an elevating platform is attached to a mast according to the present invention.
FIG. 3
shows how the elevating platform works in the stacker crane according to the present invention.
FIG. 4
is a block diagram showing how the upper and lower carts are controlled in the stacker crane according to the present invention.
FIG. 5
is a block diagram showing a variant of control of the upper and lower carts according to the present invention.
FIG. 6
is a side view of a stacker crane according to another embodiment of the present invention.
FIG. 7
is a side view showing an upper cart in the stacker crane according to the second embodiment of the present invention.
FIG. 8
shows a connection between dampers and a running unit according to the second embodiment of the present invention.
FIG. 9
shows how an elevating platform is attached to a mast according to the second embodiment of the present invention.
FIG. 10
is a characteristic diagram showing a running pattern of the stacker crane and displacement of the mast relative to the upper cart according to the second embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 1
to
4
show a stacker crane according to an embodiment of the present invention, and
FIG. 5
shows a variant of control means for upper and lower running motors. Referring to
FIG. 1
, which shows the entire stacker crane,
2
is a lower cart,
3
,
3
are running wheels,
4
is a lower running motor, and
6
is a laser range finder for determining the distance from an origin in an automatic warehouse. In addition,
8
is a common power supply for the entire stacker crane, and
10
is an elevation drive section. The stacker crane has an upper cart
12
at its top.
13
,
13
are its running wheels,
14
is an upper running motor, and
16
is a laser range finder similar to the laser range finder
6
. A mast
18
of a truss structure is provided between the upper cart
12
and the lower cart
2
, and comprises three columnar members
19
,
19
,
19
connected together using braces
20
. Although this embodiment uses the three columnar members
19
,
19
,
19
, four such members may be provided. In addition,
21
is an elevating platform elevated and lowered by the elevation drive section
10
along the mast
18
.
22
is a lower rail and
23
is an upper rail. The stacker crane is used, for example, for transferring articles in an automatic warehouse.
FIGS. 2 and 3
show how the elevating platform
21
is attached to the mast
18
and also show a slide fork
24
provided on the elevating platform
21
. The mast
18
is comprised of the columnar members
19
-
1
to
19
-
3
, and the columnar members
19
-
2
,
19
-
3
are also used as guide rails for guiding wheels
21
-
2
of the elevating platform
21
in such a manner that each of the columnar members
19
-
2
,
19
-
3
is sandwiched between the wheels
21
-
2
from the outside thereof. The slide fork
24
mounted on the elevating platform
21
has three plates
25
,
26
,
27
constructed so as to slide in a lateral direction of the stacker crane via chains.
28
,
28
are running rollers each provided on the tip plate
27
and may be wheels or balls, and
30
is a lifter provided on the tip plate
27
. The lifter
30
eliminates the need to move the plate
27
in a vertical direction of the stacker crane in loading and unloading an article
34
.
The slide fork
24
runs on a shelf support of a rack
32
using the rollers
28
,
28
to load and unload the article
34
on and from a shelf on the rack by allowing the lifter
30
to elevate and lower the article
34
. Thus, a load on the slide fork
24
is supported by the rack and is not applied to the elevating platform
21
. Thus, an unbalanced load that may be applied to the mast
18
can be prevented to enable the weight of the mast
18
to be reduced. In addition, the lifter
30
located at the tip of the slide fork
24
is used for loading and unloading the article on and from the shelf on the rack, thereby eliminating the need to slightly move the elevating platform
21
in the vertical direction in loading and unloading the article. This construction can increase the speed at which articles are loaded and transferred.
According to the embodiment, the mast
18
is formed into a truss structure in order to reduce its weight. In addition, the use of the pair of upper and lower carts
12
,
2
increases the speed at which the stacker crane operates. The mast
18
extends in the vertical direction when the upper cart
12
and the lower cart
2
overlap each other on a vertical line; in other words, when no air resistance or inertia force is applied to the mast
18
. As a result, a horizontal force applied to the mast
18
is minimized to enable the weight of the mast
18
to be further reduced. In this case, control means is correspondingly required for controlling the carts
2
,
12
in synchronism.
FIG. 4
shows a control system for motors
4
,
14
. Numeral
40
is a control section having an output VO;
41
,
42
,
44
are differentiators; and
43
is an amplifying section for applying a control gain for an output Δx (a positional value for the upper cart
12
−a positional value for the lower cart
2
) from the differentiator
44
. Numerals
6
and
16
are each the above-mentioned laser range finder for determining the distance from an origin in a warehouse of the upper cart
12
and the lower cart
2
, and SW is a switch for determining whether the upper or lower motor
14
or
4
is to be subjected to control for eliminating a positional unbalance between the upper cart
12
and the lower cart
2
(the unbalance means that Δx is not 0). According to this embodiment, the motor for a cart running ahead is controlled to decelerate so as to synchronize with the motor for a cart running behind. This construction can prevent, in any case, the upper cart
12
and the lower cart
2
from being misaligned on a vertical line due to insufficient capacity of one of the motors, or for another reason.
In
FIG. 4
, Vref is a target speed value determined based on a running pattern stored beforehand, and V
0
is a control value corresponding to the difference between the target speed value and a speed determined based on an actual position obtained, for example, by the lower laser range finder
6
. Then, the differentiator
44
checks whether the upper cart
12
or the lower cart
2
is running ahead. If the upper cart is running ahead and Δx is positive, the switch SW is connected to the differentiator
42
for control based on Equation (1).
V
up=
V
0
−
Kp·Δx−Ki∫Δx
(Δ
x>
0) (1)
That is, control based on the control target value V
0
is applied to the lower motor
4
regardless of the interrelationship with the upper motor
14
, while the upper motor
14
is subjected to a control quantity Vup comprising proportional and integral control based on Equation (1) in order to eliminate the misalignment Δx. In the above equation, Kp and Ki are control constants. Consequently, the upper cart
12
is decelerated to allow the upper cart
12
and the lower cart
2
to overlap each other on a vertical line, whereby the mast
18
accurately aligns with the vertical axis.
On the contrary, if the lower cart
2
is running ahead, Δx is negative and the switch SW is connected to the differentiator
41
. The upper motor
14
is subjected to a control quantity V
0
, whereas the lower motor
4
is subjected to a control quantity Vdown comprising proportional and integral control for eliminating the error Δx relative to the control quantity V
0
, as shown in Equation (2).
V
down=
V
0
+
Kp·Δx+Ki∫Δx
(Δ
x<
0) (2)
In place of the control in
FIG. 4
, control may be applied so that the positional error Δx between the upper cart
12
and the lower cart
2
is eliminated by the upper cart
12
side. This control is expressed by Equation (3) indicating that the lower motor
4
is controlled based on the difference between the target speed Vref and a speed determined based on a position obtained by the laser range finder
6
. The upper motor
14
is subjected to the control quantity Vup comprising proportional and integral control for eliminating the positional error Δx between the upper cart
12
and the lower cart
2
. This method can also control the upper cart
12
and the lower cart
2
in a fashion overlapping each other on a vertical line. If, however, Δx increases above the controllable range of the upper cart
12
, for example, if the upper cart
12
cannot catch up with the lower cart
2
despite the rotation of the upper running motor
14
with its full power, then Δx cannot be eliminated during running, thereby requiring the stacker crane to be stopped.
V
up=
V
0
−
Kp·Δx−Ki∫Δx
(3)
FIGS. 6
to
9
show a stacker crane according to another embodiment, and
FIG. 10
shows a running pattern of this stacker crane. Referring to
FIG. 6
, which shows the entire stacker crane,
104
is a lower cart,
106
is an upper cart, and the carts are each comprised of a running unit
108
and a connection unit
110
elastically connected thereto.
112
is a mast adapted to have a truss structure obtained, for example, by coupling three columnar members
114
,
114
,
114
together via braces
115
. The mast
112
is, for example, 30 m in height and is fixed to the lower cart
104
and the connection unit
110
.
116
is an elevating platform that elevates and lowers along the mast
112
, and
118
is an elevation drive section.
119
is a laser range finder for detecting the absolute positions of the carts
104
,
106
.
120
is an upper rail and
121
is a lower rail. The stacker crane is used, for example, for transferring articles in an automatic warehouse.
FIG. 7
shows an elastic connection between the running unit
108
and the connection unit
110
. The connection unit
110
has an upper end of the mast
112
secured thereto. The running unit
108
runs along the upper rail
120
, and is elastically connected to the connection unit
110
to avoid an excess force that may be applied to the connection. The running unit
108
has guide rollers
122
,
123
,
124
provided thereon and guided by the upper rail
120
, and is run when running wheels
126
are driven by a running motor
125
. An arm
128
provided on the running unit
108
has, for example, a pair of dampers
130
,
130
connected thereto and provided on the connection unit for preventing vibration of the mast
112
. The dampers
130
are each composed of an electromagnetic or oil damper and have a bar-shaped member
131
located at a tip thereof and abutting on a plate-like member
129
fixed to the arm
128
for vertical and lateral movements. This construction allows only the contact position between the bar-shaped member
131
and the plate-like member
129
to be moved despite deformation of the mast
112
, for example, its deflection, thereby avoiding application of an excess force.
The running unit
108
has an arm
132
provided thereon and to which springs
134
,
134
on the connection unit
110
, for example, spring coils, laminate springs, or ring springs, are connected from opposite sides of the arm
132
. Thus, a force applied from the running unit
108
to the connection unit
110
in the direction of the rail
120
(a thrust acting in the running direction) is applied depending on displacement of the springs
134
. This thrust is not necessarily proportional to the displacement. If the springs
134
,
134
have a high damping capability or undergo a large friction when displaced, they act as dampers to eliminate the need for the dampers
130
,
130
. On the contrary, if the dampers
130
,
130
provide a spring capability at opposite ends of a stroke, then they serve to eliminate the need for the springs
134
. Numeral
136
is a detection arm of the running unit
108
, and
138
,
138
are limit switches for detecting a position of the detection an
136
and must only be capable of detecting that displacement between the running unit
108
and the connection unit
110
located below it corresponds to a predetermined value or greater. Numeral
140
is a sheave for a lifting wire
142
for the elevating platform.
FIG. 9
shows how the elevating platform
116
is attached to the mast
112
. The mast
112
is comprised, for example, of the three columnar members
114
, and two of these columnar members are also used as guide rails so that guide rollers
144
of the elevating platform
116
each elevate and lower in a manner sandwiching a corresponding one of the columnar members
114
from opposite sides thereof. A transfer means such as a slide fork
148
is mounted on a pallet
146
of the elevating platform
116
.
According to this embodiment, the mast
112
is formed into a truss structure in order to reduce its weight. In addition, the use of the pair of the upper cart
106
and lower cart
104
increases the speed at which the stacker crane operates. Correspondingly, a relatively large force is applied between the connection unit
110
and the running unit
108
, but is absorbed by the springs
134
,
134
, and vibration of the mast
112
is absorbed by the dampers
130
,
130
. On the contrary, the running unit
108
transmits a thrust to the connection unit
110
via the springs
134
,
134
, wherein the thrust is equal to inertia force or air resistance acting on an upper part of the mast
112
.
FIG. 10
shows a speed pattern of the stacker crane and displacement of the springs
134
,
134
. Due to its small weight and large thrust, the stacker crane accelerates at an acceleration about five times as large as that in the prior art (area P
1
), runs at a speed about twice as that in the prior art (area P
2
), decelerates at a deceleration about five times as large as that in the prior art (area P
3
), and stops after running over a short distance at a low speed (area P
4
). Accordingly, if the connection unit
110
is secured to the running unit
108
so as to be prevented from displacement, a large force is applied between these units. In contrast, since the connection unit
110
is elastically connected to the running unit
108
, these units are prevented from being subjected to an excess force. In addition, the dampers
130
prevent the mast
112
from vibrating associated with fast running or a high acceleration or deceleration.
In the area P
1
, a force required for accelerating the mast
112
and a thrust corresponding to air resistance are applied via the springs
134
, in the area P
2
, the thrust corresponding to the air resistance is applied via the springs
134
, in the area P
3
, a braking force is applied corresponding to the difference between an inertia force associated with deceleration and the air resistance, and in the area P
4
, an error in deceleration control is eliminated and vibration of the mast
112
is stopped, followed by stoppage at a target shelf. Thus, an excess force that may be applied to the upper cart
106
is avoided and the running time of the stacker crane is reduced to improve its transfer capability.
Claims
- 1. A stacker crane having a vertically extending mast containing an elevating platform and being attached between an upper cart and a lower cart, and means for maintaining said mast in a vertical attitude, comprising:vertically spaced upper and lower rails, said upper and lower carts connecting the upper and lower ends, respectively, of said mast, said carts each having runner wheels engaging said upper and lower rails, respectively, separate running motors operable to drive each of said carts, and control means for controlling at least one of said running motors so that the upper and lower carts overlie each other on a vertical line, said control means comprising: a laser operated range finder associated with each of said carts, and a control system operative to activate the running motor of at least one of said carts for moving said at least one cart in response to a comparison of signals generated by said range finders.
- 2. A stacker crane as in claim 1, characterized in that said mast is connected to said one of the carts via dampers.
- 3. A stacker crane according to claim 1 in which the mast of the stacker crane is formed as a truss structure.
- 4. A stacker crane according to claim 1 in which said control system is configured to effect overlapping of said upper and lower carts on a vertical line by controlling the running motor for the cart running ahead in a manner synchronously with the running motor of the cart running behind.
- 5. A stacker crane according to claim 4, characterized in that the mast of the stacker crane is formed as a truss structure.
Priority Claims (2)
Number |
Date |
Country |
Kind |
11-163396 |
Jun 1999 |
JP |
|
11-163397 |
Jun 1999 |
JP |
|
US Referenced Citations (7)
Foreign Referenced Citations (2)
Number |
Date |
Country |
6-100109 |
Apr 1994 |
JP |
6-25444 |
Jul 1994 |
JP |