Field of Invention:
The present invention relates to an apparatus and mechanism facilitating precise
motion in forward and reverse direction of spreader bar used in separating sheets
of a tubular fabric used for sack making.
5
Background of Invention:
In the processing of tubular woven fabric for making sacks for packing
applications, it is common to form valves for filling material such as cement or
any other kind of powdery or granular raw materials such as sand, grain etc. into
10 sacks. Conventionally, these valves are formed manually by opening the sacks at
their one corner and forming a filling mouth. These conventional methods of
making valves or creases at one end of tubular sacks are time consuming,
especially as the production demand for the bags/sacks with valves increases.
15 In order to overcome this issue, conventionally, an apparatus is developed
comprising a flat bar known as spreader bar, and a mechanism to drive these
spreader bars linearly along a horizontal plane such that it pushes the sack fabric
to form a triangular fold, which is later converted into an inward fold and
ultimately a valve opening after further processing.
20
The flat bar adapted for separating two layers of fabric, which can be polyolefin
woven sacks or any other kind of sacks made of like materials.
3
With the increase in demand for woven sacks, there has been an increase in the
automation of their manufacture, especially of the cutting and stitching stages.
The tubular fabric is cut into pieces of required length, which are further
transformed by stitching them at one end. At the other end of the cut pieces—the
un-stitched end—the layers of the fabric are separated 5 by using a parting
mechanism. The spreader bar is pushed forward such that it form triangular fold at
the fabric corner and retracted back, thereafter facilitating transformation of
triangular folds into inward corner fold of tubular fabric. This forward and
backward motion of spreader bar during folding process needs very precise
10 synchronization with dynamics of entire cutting, stitching and valve forming
machine. Any small phase lag between the motion of the spreader bar and the
motion of other parts of the sack forming apparatus can lead to distortion of shape
or misalignment of tubular fabric which further results in faulty stitching or
formation of incorrectly shaped valve.
15
Traditionally, spreader bars are linked with various mechanical components to
actuate their motion. Reliability and adjustment of these linkages play very
important role in the positioning of the spreader bars and machine operations in
general. However, the settings of spreader bars and linkages deteriorate over time
20 leading to their wear and tear. This adversely affects desired accuracy of spreader
bar positioning with respect to travelling fabric.
4
There is a need for a reliable automated method to synchronize the movements of
the spreader bar and those of other moving parts of a sack making apparatus.
Objects of the invention:
It is, accordingly, an object of the present invention, to provide 5 an efficient and
precise mechanism in which spreader bar telescopic motion can be effectively
controlled in real-time, maintaining utmost functional accuracy.
A further object of the invention is to develop a mechanism which requires
10 minimum maintenance due to rapid reciprocating motion of assembly
components.
The objects and advantages thereof may be understood by making reference to the
following description, along with the accompanying drawings.
15
List of parts:
Spreader bar (1)
Linear motion guide (2)
Driving belt (3)
Driving Roller (4)
Second sensor (4A)
Speed reduction gear box (4B)
Output shaft (4C)
Servo Mechanism (5)
Servo Driver (5A)
Central Processing Unit or a PLC (5B)
Memory Unit (5C)
Encoder Unit (5D)
5
Servo Motor (6)
Motor unit (6A)
Tubular fabric (7)
Conveyor means (8)
Suction means (9)
Pivot (10)
Brief description of figures:
Figure 1 shows flow-diagram for process of valve making in a pillow-shaped sack
Figure 2 shows the stages of sacks as it undergoes the manufacturing process
Figure 3 shows the pre-operational position of a spreader bar 5 that operates in a
linear mode
Figure 4 shows a schematic of Spreader bar forward motion
Figure 5 shows a schematic of Spreader bar reverse motion
Figure 6 shows a block diagram representation of the Servo system
10 Figure 7 shows a representation of the spreader bar that works in a rotational
mode
Summary of Invention:
The present invention discloses a device and a method for facilitating precise
15 motion in forward and reverse direction of spreader bar used in separating sheets
of a tubular fabric used for sack making on an automated sack-making machine.
The device uses a servo mechanism incorporating sensors, servo motors and
drivers arranged to provide continuous monitoring of the spreader bar motion and
the sack fabric movement, and uses appropriate feedback loop to ensure
6
synchronization between and alignment of the sack moving along the conveyor
platform and the spreader bar that is employed to separate the individual layers of
the sack fabric in order to ultimately make an inward fold for valve making. A
method for accurate control of the spreader bar motion is also proposed. The
invention allows to overcome the problems of misalignment 5 and helps prevent the
damage caused by it, thereby increasing the operational life of the machine.
Detailed Description of invention:
The present invention is used in machines for processing of fabrics, papers and
10 the like materials. The fabric may be non-woven or woven tubular fabric made
from monoaxially stretched tapes. (In the upcoming description, we will use the
term sack fabric or tubular fabric interchangeably.)
Figure 1 shows flow-diagram for process of valve making in a pillow-shaped
15 sack. The present invention – one that involving a spreader bar (1) – comes into
picture in conjunction with a fold forming and crease forming device.
Figure 2 shows shows the stages of a typical sacks manufacturing process
pictorially illustrating how a sack with a valve is formed. Here the spreader bar
20 (1) of the invention is used in forming stage E. The sequence may vary and what
has been shown in Figure 2 is for illustrative purpose only.
7
In such machines it is often required to spread or open the tubular fabric (7) sheet
mouth by separating its individual layers, or fold fabrics or carry out similar
activities, as the tubular fabric (7) sheet travels from one processing point to
another. Figure 3 illustrates the fabric (7) with separated layers and where the
spreader bar (1) is positioned. Figure 3 shows some of the typical 5 parts used on a
sack-making line – namely a conveyor platform, suction means (8) used to
separate the individual fabric layers, and a stamper to form creases. Depending on
the type of the sack making apparatus, different components may be used.
10 Conventionally, methods often used to advance a spreader bar into the opening
between the individual sack layers, or to retract spreader bar once the folding
operation is over, are able to synchronize spreader bar movement with moving
components of other processing stations. So long as the spreader bar motion is
aligned with the movement of fabric (7) including separation of individual layers
15 of the fabric, the force applied by the flat bar pushes the fabric (7) evenly and the
triangular fold formed is perfect in shape. However, when the fabric (7) and the
bar (1) are misaligned or are out of synchronization with each other, the force
applied by bar forms undesired fold shape on fabric (7). In order to overcome the
problem of misalignment and to prevent the damage caused by it, the present
20 invention provides a spreader bar (1) that is operated by servo mechanism (5) to
provide high operational accuracy.
8
For the purpose of this invention the terms 'synchronization' and 'alignment' are
defined as thus:
- synchronization indicates the state in time domain where the timing of
events is such that a specific outcome is achieved. In the case of this
invention, the timing of the movement of the spreader 5 bar (1) and the
timing of its positioning at a desired location is such that it gets inserted in
between the two separated layers of the sack fabric (7) with ease, forms a
triangular fold, and retracts with ease.
- Alignment indicates a state in spatial domain where the position of the
10 spreader bar (1) is such that it gets inserted in between the two separated
layers of the sack fabric (7) with ease, forms a triangular fold, and retracts
with ease.
Figure 4 provides a partial view of invention comprising spreader bar mechanism,
15 driven by an encoder-based rotary actuator drive/servo controlled system, which
can be controlled by main programmable logic controller (PLC), also referred to
as a motion controller. In comparison to other proposed controlling systems, a
servo-controlled mechanism provides a more precise and accurate positioning of
spreader bar in relation to the travelling fabric (7).
20
Figure 4 shows a spreader bar (1) that moves along the linear motion guide (2) as
a driving belt (3) connected to the spreader bar moves on a set of rotating driving
9
rollers (4), such that spreader bar (1) motion along the linear motion guide (2) is
perfectly aligned with travelling fabric (7) by using a PLC (5B) and a first sensor
(which is a positional sensor – not shown in figures). The driving belt (3) is a
timing belt (a flexible belt with teeth moulded onto its inner surface), and
correspondingly the driving rollers (4) are a timing type pulley 5 (a pulley provided
with toothed outer surface) such that the driving rollers (4) and the driving belt (3)
have a non-slipping contact when the driving rollers (4) are being driven by the
driving belt (3).
10 In its operational state, the spreader bar (1) moves in direction ‘a’ (forward
movement) as unstitched fabric-end reaches in front of the spreader bar (1) and it
pushes back the upper layer of the fabric to form a triangular fold (see Figure 2,
stage E). The spreader bar’s (1) initial positioning, its forward movement, and the
positioning of the fabric (7) are all aligned with the help of the first sensors
15 provided at appropriate location on the sack-making machine; the first sensors
being used for indicating arriving position of fabric (7) when it reaches near to the
spreader bar (1). Similarly, the spreader bar's (1) acceleration from its state of rest
at its original position, its maximum forward speed, and decelerate to come to a
state of rest at the end of the distance it's designed to travel on its way forward.
20
In the forward motion (indicated by the arrow 'a' in Figure 4) of the spreader bar
(1), the encoder (5D) (see Figure 6) monitors the rotations of the servo motor (6).
10
The PLC (5B) controls the start time of the spreader bar (1) motion, following
which there's continuous communication through a feedback loop between the
servo motor (6) and the servo driver (5). The servo motor (6) in turn drives,
through an output shaft (4C), the driving rollers (4) that further provide movement
to the spreader bar (1). A set of second sensors (4A), also 5 termed as driving
sensors, is provided to monitor the movement of the driving rollers (4) and send a
control feedback to the PLC (5B), which, based on the control feedback, controls
the movement of the servo motor (6) to continue or stop the forward movement of
the spreader bar (1). One second sensor (4A) is provided for each of the driving
10 rollers (4). The reverse motion of the spreader bar (1) is monitored along the same
principle of comparing the feedbacks of the servo motor (6) rotation and the
actual measured movement of the spreader bar (1).
Figure 5 shows the spreader bar (1) in a retracted position. The driving rollers (4)
15 are rotated in reverse direction (to the direction of rotation required for the
forward motion of the spreader bar) to retract the spreader bar (1) along the linear
guide (2) axis (i.e. in direction ‘b’ shown in Figure 5). In a manner similar to its
forward movement, in the reverse movement of the spreader bar, the spreader
bar's (1) acceleration from its state of rest, its maximum travel speed, and
20 decelerate to come to a state of rest at the end of the distance it's designed to
travel on its way back to its original position. The reverse movement of the
spreader bar (1) (see Figure 5) is controlled using similar parameters
11
(acceleration, deceleration and the distance travelled) by the servo mechanism (5)
of the invention.
Servo mechanisms/motors are well known to a person skilled in the art. There are
a number of applications, such as the present invention, where 5 a limited rotation
or movement (over a period of a few seconds or even a fraction of a second) of a
motor-based component is required, rather than continuous repetitive movement
over a long period of time. For such applications, specially designed motors are
provided in special arrangements so that the motors move in certain angle under a
10 given electric input. Some commonly known applications are robotics, CNC
machniery. A closed loop feedback control system using a servo mechanism (5)
used for the present invention is shown in Figure 6.
In an embodiment of the invention, the driving rollers (4) are coupled with servo
15 motors which in turn are controlled in real time by electronically controlled closed
loop system for accurate positioning.
One of the preferred embodiments of the invention is the specially designed servo
mechanism (5), as indicated in the block diagram of Figure 6. It comprises of a
20 servo driver (5) which further includes a memory unit (5C), a servo motor (6)
which further includes a motor unit (6A) and an encoder unit (5D). In general, a
servo control system is a motion controlled system for position and
12
acceleration/deceleration controlling through close loop feedback system
completed based on the encoder unit feedback.
The function of a servo driver (5) along with the encoder unit is to provide a close
loop control for the entire servo system. The data parameters 5 of control of the
servo motor (6) are saved in memory unit (5C), included in Servo driver (5).
The spreader bar (1) positioning along the linear motion guide (2) is achieved by
rotation of driving rollers (4). The function of driving rollers (4) is to provide
10 driving force for spreader bar (1) movement. These driving rollers (4) can be
directly coupled to servo motor (6) or by speed reduction gear box (4B).
In the operational state of the spreader bar (1), the encoder unit sends the realtime
angular position of the servo motor shaft to the servo driver (5). As a result,
15 the servo driver unit (5) receives information on real-time position of the driving
roller (4) which is further compared with the desired value which is already prestored/
input/saved in the memory unit (5C). On the basis of this information,
action is taken as to whether to command the motor unit (6A) for motion or to
stop it. This stepwise control of motor unit (6A) in closed loop system increases
20 accuracy of the position of the driving rollers (4), and as a result, the accuracy of
the positioning of the spreading bar (1).
13
The spreader bar (1) movement may be orthogonal or perpendicular to the
direction of movement of the fabric (7) that's fed on a conveyor system of the
sack-making machine. In this case, the spreader bar movement may be termed as
axial movement.
5
In another embodiment, it is possible to provide a mechanism by which the
spreader bar (1) moves in the plane of the fabric (7) by rotating around a pivot. In
this case (refer to Figure 7), the spreader bar movement is termed as the rotational
movement. In this embodiment, the forward (indicated by the curved arrow 'c')
10 and reverse (indicated by the curved arrow 'd') movements are rotational. For
example, the forward movement is the rotational movement of the spreader bar
that allows formation of an inward fold in one corner of the sack. The reverse
movement would be the rotational movement that allows the spreader bar to come
out of the fabric.
15
It is possible to provide a combination of the axial and rotational movements. For
example, the spreader bar may move axially in order to enter between the
separated layers of the fabric and upon entry, it may move rotationally in order to
create the inward folded valve.
20
In conventional sack making machines, the spreader bar movement can be jerky,
with sudden and haphazard acceleration/deceleration and starts and stops. The
14
mechanical components of the conventional spreader bar assemblies are liable to
suffer unnecessary wear due to this, which results into reduced life. These
problems are eliminated by the present invention which provides increased life of
the spreader bar assembly.
5
It is evident from the foregoing discussion that the present invention has a number
of embodiments as disclosed below.
1. A device for controlling the motion of a spreader bar (1) in an automated sack
making apparatus, said spreader bar (1) being used for making a fold at a
10 corner of a tubular fabric (7) having separated individual layers, characterized
said device comprises a servo mechanism (5) to control the movement of said
spreader (1), wherein said servo mechanism (5) in turn comprises at least one
servo motor (6), and a servo driver (5A).
2. A device for controlling the motion of a spreader bar as disclosed in
15 embodiment 1, characterized in that said servo driver (5A) comprises a
memory unit (5C), and an encoder unit (5D) that monitors the rotations of
said servo motor (6).
3. A device for controlling the motion of a spreader bar as disclosed in
embodiments 1-2, characterized in that a second sensor monitors the
20 movement of a set of driving rollers (4) which are driven by a driving belt (3)
and sends a control feedback to a programmable logic control (5B) unit,
which, based on the control feedback, controls the movement of the servo
15
motor (6) to continue or stop the forward or reverse movements of the
spreader bar (1) through said servo driver (5A).
4. A device for controlling the motion of a spreader bar as disclosed in
embodiments 1-3, characterized in that each of said servo motors (6) is
directly coupled to said 5 spreader bar (1).
5. A device for controlling the motion of a spreader bar as disclosed in
embodiments 1-3, characterized in that each of said servo motors (6) is
connected to said spreader bar (1) through a belt-link assembly and driving
roller (4).
10 6. A device for controlling the motion of a spreader bar as disclosed in
embodiments 1-5, characterized in that each of said servo motors (6) is
connected to said spreader bar (1) through output shaft (4C) of speed
reduction gear box (4B).
7. A device for controlling the motion of a spreader bar as disclosed in
15 embodiments 1-6 characterized in that said driving rollers (4) are coupled
with said servo motors (6) which in turn are controlled through real time
electronically controlled closed loop system for accurate positioning of said
spreader bar (1).
8. A device for controlling the motion of a spreader bar as disclosed in
20 embodiments 1-7, characterized in that said spreader bar (1) is capable of
moving backwards and forwards along a linear motion guide (2) and in the
plane of sack fabric (7) and in a direction that is substantially orthogonal to
16
the direction of the movement of the sack fabric (1) on the sack conveyor belt
(8).
9. A device for controlling the motion of a spreader bar (1) as disclosed in
embodiments 1-7, characterized in that said spreader bar (1) is capable of
moving forward and backwards around a pivot (10) such that 5 once it enters
between the separated layers of said fabric (7), it is makes a sweeping action
around the pivot (10) to make said inward fold and retracts after formation of
the fold.
10. A device for controlling the motion of a spreader bar (1) as disclosed in
10 embodiments 1-8, characterized in that said servo motor (6) is oriented such
that its rotational axis is substantially parallel to the direction of movement of
the fabric (7) on the conveyor belt (8).
11. A device for controlling the motion of a spreader bar (1) as disclosed in
embodiments 1-8, and 10, characterized in that said servo motor (6) is
15 oriented such that its rotational axis is substantially perpendicular to the plane
of movement of said fabric (7).
12. A device for controlling the motion of a spreader bar (1) as disclosed in
embodiments 1-8, 10, and 11, characterized in that said driving rollers (4) and
said driving belt (3) are, respectively, pulleys and a belt, wherein the contact
20 between said pulley and said belt is non-slipping.
13. A device for controlling the motion of a spreader bar (1) as disclosed in
embodiments 1-8, and 10-12, characterized in that said driving roller (4) has
17
teeth on its outer surface and said driving belt (3) has a corresponding teethed
inner surface for contact with said driving roller (4).
14. A method of controlling the motion of a spreader bar (1) in an automated
sack making apparatus characterized in that said method comprises a step of
controlling positioning of spreader bar (1), and its 5 acceleration and
deceleration during its forward movement, and also its acceleration and
deceleration in its reverse movement precisely and accurately using a servo
mechanism (5) in relation to the travelling fabric (7).
15. A method of controlling the motion of a spreader bar as disclosed in
10 embodiment 12, wherein said method comprises the steps of:
- providing a device as claimed in any of claims 1 to 12,
- sending via the encoder unit (5D), a signal with real-time angular position
of the servo motor shaft to the servo driver (5A),
- compared the real-time angular position of the servo motor shaft with the
15 desired value which is pre-stored/input/saved in the memory unit (5C),
- on the basis of the outcome of comparison, sending a command to the
motor unit ( (6A) for continuing the motion of the spreader bar (1) or for
stopping it.
20 While the above description contains much specificity, these should not be
construed as limitation in the scope of the invention, but rather as an
exemplification of the preferred embodiments thereof. It must be realized that
18
modifications and variations are possible based on the disclosure given above
without departing from the spirit and scope of the invention. Accordingly, the
scope of the invention should be determined not by the embodiments illustrated,
but by the appended claims and their legal equivalents.

We claim:
1. A device for controlling the motion of a spreader bar (1) in an automated sack
making apparatus, said spreader bar (1) being used for making a triangular
fold at a corner of a tubular fabric (7) having separated individual layers,
characterized said device comprises a servo mechanism 5 to control the
movement of said spreader (1), wherein said servo mechanism (5) in turn
comprises at least one servo motor (6), and a servo driver (5A).
2. A device for controlling the motion of a spreader bar as claimed in claim 1,
characterized in that said servo driver (5A) comprises a memory unit (5C),
10 and an encoder unit (5D) that monitors the rotations of said servo motor (6).
3. A device for controlling the motion of a spreader bar as claimed in claims 1-
2, characterized in that a second sensor monitors the movement of a set of
driving rollers (4) which are driven by a driving belt (3) and sends a control
feedback to a programmable logic control unit, which, based on the control
15 feedback, controls the movement of the servo motor (6) to continue or stop
the forward or reverse movements of the spreader bar (1) through said servo
driver (5A).
4. A device for controlling the motion of a spreader bar as claimed in claims 1-
3, characterized in that each of said servo motors (6) is directly coupled to
20 said spreader bar (1).
20
5. A device for controlling the motion of a spreader bar (1) as claimed in claims
1-3, characterized in that each of said servo motors(6) is connected to said
spreader bar (1) through a belt and link assembly and a driving roller (4).
6. A device for controlling the motion of a spreader bar as disclosed in
embodiments 1-5, characterized in that each of said servo 5 motors (6) is
connected to said spreader bar (1) through output shaft (4C) of speed
reduction gear box (4B).
7. A device for controlling the motion of a spreader bar (1) as claimed in claims
1-6 characterized in that said driving rollers (4) are coupled with said servo
10 motors (6) which in turn are controlled through real time electronically
controlled closed loop system for accurate positioning of said spreader bar
(1).
8. A device for controlling the motion of a spreader bar (1) as claimed in
claims1-7, characterized in that said spreader bar (1) is capable of moving
15 backwards and forwards along a linear motion guide (2) and in the plane of
sack fabric (7) and in a direction that is substantially orthogonal to the
direction of the movement of the sack fabric (7) on the sack conveyor belt
(8).
9. A device for controlling the motion of a spreader bar (1) as claimed in
20 claims1-7, characterized in that said spreader bar (1) is capable of moving
forward and backwards around a pivot (1) such that once it enters between
the separated layers of said fabric (7), it is makes a sweeping action around
21
the pivot (10) to make said inward fold and retracts after formation of the
fold.
10. A device for controlling the motion of a spreader bar (1) as claimed in
claims1-8, characterized in that said servo motor (6) is oriented such that its
rotational axis is substantially parallel to the direction 5 of movement of the
fabric (7) on the conveyor belt (8).
11. A device for controlling the motion of a spreader bar (1) as claimed in
claims1-8, and 10, characterized in that said servo motor (6) is oriented such
that its rotational axis is substantially perpendicular to the plane of movement
10 of said fabric (7).
12. A device for controlling the motion of a spreader bar (1) as claimed claims 1-
8, 10 and 11, characterized in that said driving rollers (4) and said driving belt
(3) are, respectively, pulleys and a belt, wherein the contact between said
pulley and said belt is non-slipping.
15 13. A device for controlling the motion of a spreader bar (1) as claimed claims 1-
8, and 10-12, characterized in that said driving roller (4) has teeth on its outer
surface and said driving belt (3) has a corresponding teethed inner surface for
contact with said driving roller (4).
14. A method of controlling the motion of a spreader bar (1) in an automated
20 sack making apparatus characterized in that said method comprises a step of
controlling positioning of spreader bar (1), and its acceleration during its
forward movement, and its deceleration in its reverse movement precisely
22
and accurately using a servo mechanism (5) in relation to the travelling fabric
(7).
15. A method of controlling the motion of a spreader bar as claimed in claim 12,
wherein said method comprises the steps of:
- providing a device as claimed in any 5 of claims 1 to 12,
- sending via the encoder unit (5D), a signal with real-time angular
position of the servo motor shaft to the servo driver (5A),
- compared the real-time angular position of the servo motor shaft with
the desired value which is pre-stored/input/saved in the memory unit
10 (5C),
- on the basis of the outcome of comparison, sending a command to the
motor unit (6A) for continuing the motion of the spreader bar (1) or for
stopping it.