Data processing: generic control systems or specific application – Specific application – apparatus or process – Article handling
Reexamination Certificate
2000-11-03
2004-04-06
Walsh, Donald P. (Department: 3653)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Article handling
C700S245000, C700S257000, C414S749100, C414S799000
Reexamination Certificate
active
06718229
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to automated assembly systems employing linear drive mechanisms, and more particularly to a system for performing palletizing using a plurality of linear actuators having associated controllers, and to a program which facilitates entry of palletizing parameters to the controllers, for controlling action of the linear actuators according to preset palletizing conditions.
2. Background of the Invention
Linear actuators have been widely used in automated assembly procedures due to their inherent robustness, ease of variation in size and configuration, and the accuracy with which such actuators can be controlled to transport parts or tools to a precise location while following tightly controlled patterns of movement.
A known type of electric linear actuator, to which the principles of the present invention are applied, is shown in
FIGS. 1 through 3
.
The electric actuator, generally denoted at
50
in
FIGS. 1 through 3
, comprises an elongate frame
52
as a base, a pair of elongate side covers
54
a
,
54
b
mounted respectively on transversely opposite sides of the frame
52
, a pair of end covers
56
,
57
mounted respectively on longitudinally opposite ends of the frame
52
, and an elongate top cover
58
engaging upper surfaces of the side covers
54
a
,
54
b.
On the frame
52
, there are mounted a drive mechanism
60
fixed to one end of the frame
52
and supporting one end of a ball screw
62
, a bearing block
64
fixed to the other end of the frame
52
and supporting the other end of the ball screw
62
, and a table mechanism
66
linearly displaceable between the drive mechanism
60
and the bearing block
64
by the ball screw
62
upon rotation thereof. A pair of transversely spaced guide members
68
a
,
68
b
is fixed to an upper surface of the frame
52
for linearly guiding the table mechanism
66
when the table mechanism
66
is displaced by the ball screw
62
. The bearing block
64
comprises a support block
22
mounted on the frame
52
, and the other end of the ball screw
62
is rotatably supported in the support block
22
by a bearing
24
.
The frame
52
has two transversely spaced grooves
70
a
,
70
b
of an identical T-shaped cross section which are defined in a lower surface thereof and extend parallel to each other in the longitudinal direction of the frame
52
. The transversely opposite sides of the frame
52
have respective engaging grooves
72
a
,
72
b
defined therein and extending longitudinally therealong for attachment of the side covers
54
a
,
54
b
. The frame
52
also has longitudinal passageways
74
a
,
74
b
,
76
a
,
76
b
defined therein for accommodating electric wires or hydraulic fluid conduits. The frame
52
has a pair of attachment grooves
77
a
,
77
b
defined in an upper surface thereof near the passageways
76
a
,
76
b
for attachment of detectors such as automatic switches or the like. The attachment grooves
77
a
,
77
b
also serve as wiring grooves for accommodating leads connected to the detectors.
The side covers
54
a
,
54
b
have respective substantially L-shaped hooks
78
a
,
78
b
disposed on inner sides thereof for engaging in the respective engaging grooves
72
a
,
72
b
. The hooks
78
a
,
78
b
can be fitted into respective engaging grooves
72
a
,
72
b
when the side covers
54
a
,
54
b
are pressed obliquely downward against the transversely opposite sides, respectively, of the frame
52
. To detach the side covers
54
a
,
54
b
from the frame
52
, the side covers
54
a
,
54
b
are pulled upwardly away from the transversely opposite sides, respectively, of the frame
52
. Therefore, the side covers
54
a
,
54
b
can easily be installed on and removed from the frame
52
.
As shown in
FIG. 2
, the table mechanism
66
comprises a ball screw bushing
80
for converting rotary motion of the ball screw
62
into linear motion, a pair of table blocks
82
a
,
82
b
holding transversely opposite sides, respectively, of the ball screw bushing
80
, and a pair of holders
84
a
,
84
b
having a channel-shaped cross section interposed between the table blocks
82
a
;
82
b
and the guide members
68
a
,
68
b
. As shown in
FIG. 1
, the table blocks
82
a
,
82
b
have holes
86
defined in their upper surfaces for coupling a member that is mounted on the table blocks
82
a
,
82
b
, and the table block
82
b
has a recess
88
defined in its upper surface for positioning a workpiece highly accurately.
In the case of multi-axis configurations, the table blocks
82
a
,
82
b
can support yet another linear actuator thereon, to enable the movement of a table block of the thus-supported actuator in both X and Y directions, for example.
As shown in
FIG. 3
, the drive mechanism
60
comprises a housing
106
mounted on the frame
52
and having a bearing
104
to which one end of the ball screw
62
is rotatably supported, a motor
108
, and an encoder
112
covered by a cover
110
. The housing
106
which supports the ball screw
62
serves as a motor body.
The motor
108
is fixed to the housing
106
, and comprises a stator
116
composed of a plurality of separate stator cores
114
that are joined together, a plurality of coils
118
wound around the respective stator cores
114
, and an annular permanent magnet
122
serving as a rotor which is fixedly mounted on a reduced-diameter end
62
a
of the ball screw
62
through a sleeve
120
.
As shall be explained in greater detail in connection with the preferred embodiments of the invention, typically a linear actuator, such as the one described above, will be provided as only one actuator in a multi-axis system of actuators, which are connected together as a structural system, for enabling movement of an end effector (for example a gripping tool) in two or more dimensions, for picking up objects (parts) and delivering them to a desired destination, for example an assembly station.
In many assembly operations, a plurality of identical parts for assembly are arranged in a specified array inside a pallet, in an ordered pattern of rows and columns, and the parts are required to be delivered sequentially to an assembly station where the parts are assembled onto another component located in the assembly station. In such a situation, it is convenient to undertake a so called palletizing operation. More specifically, a gripping tool which is movable under the power of actuators is moved to a first position to pick up a first part in the pallet array, grip the part and deliver it to an assembly position where the part is assembled onto another, usually larger, component. After the part is assembled onto the component, the actuators are again driven to return the gripping tool to the pallet array, however, at this time the gripping member is controlled through a series of pre-stored movement patterns to be indexed to the next part in the array (for example, the part in the next column of the first row) so that the second part is then picked up and delivered to the assembly station for assembly onto the same or another component. When the first row of parts has been completed, the actuator can be indexed to the next row, proceeding in sequence until all parts in the pallet have been delivered to the assembly station.
Typically, movement of a linear actuator is controlled by inputting into a stored motion profile table (MPT) various parameters to control movement of the table blocks
82
a
,
82
b
or any member attached to the table blocks, at a set acceleration, velocity and deceleration, until reaching the desired position. A plurality of pre-programmed movements are each stored in the motion profile table as steps, wherein each step moves the table blocks
82
a
,
82
b
to one predetermined position according to a given acceleration-velocity-deceleration profile. When a series of movements is to be performed in sequence, a plurality of steps must first be pre-programmed and stored, and then the series of steps is run in a chosen order dictated by a Programmable Logic C
Hudson Kevin
Takebayashi Takashi
Guss Paul A.
Shapiro Jeffery A
SMC Kabushiki Kaisha
Walsh Donald P.
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