Measuring and testing – Specimen stress or strain – or testing by stress or strain... – By loading of specimen
Reexamination Certificate
1999-11-23
2002-08-20
Noori, Max (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
By loading of specimen
Reexamination Certificate
active
06435035
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to an apparatus and method for monitoring chain pull or tension, and in particular, to the use of a load cell-type force sensor positioned between components of a chain drive for tension monitoring.
BACKGROUND ART
Conveyor systems using chains as the driving mechanism and chain drives to give the conveyor motion and control conveyor speed are well known in the art. One example of these types of conveyor systems is a power and free system. Power and free systems are generally made up of a power track, a free track, and trolleys capable of travelling along the free track, the trolleys supporting one or more carriers. Each carrier then supports a load or article being conveyed. The trolleys are usually divided into leading and trailing trolleys. Each leading trolley in a power and free system includes a driving dog portion which extends towards the power track and which is engageable by a pusher dog carried by a moving chain on the power track. When the pusher dog and the driving dog are engaged, the leading or drive trolleys push along the free track by the moving power chain. When the driving dog is retracted, or otherwise disengaged from the pusher dog, the trolley stops moving, thus halting the carrier.
To move the power chain, one or more conveyor drives are utilized. Two typical types include caterpillar and sprocket versions. A sprocket drive delivers motion to the conveyor chain directly from the output side of a reducer through a sprocket whose teeth mesh with the lengths of the conveyor chain. A caterpillar drive transmits its driving force to the conveyor by means of a caterpillar chain made of precision steel rollers with driving dogs that mesh with the lengths of the conveyor chain. Depending on the size of the conveyor system, the drives can provide chain pulls of up to 12,000 pounds.
Caterpillar drives come generally in junior or standard categories. The smaller drives can be designed with either a fixed frame or a floating frame. Larger drives generally use floating frames. Caterpillar drives are usually installed along any horizontal straight run of a conveyor track.
Standard floating drives can be either a linear type or a rotary type. The linear type is generally built with an inner floating frame that is guided and supported by ball bearing wheels attached to an outer fixed frame. In contrast, a rotary drive is mounted on an inner floating frame that pivots around a reducer output shaft, the floating frame acting as a torque arm against the fixed outer frame. One or more compact coil springs counterbalance the normal chain pull and control the movement of the floating frame.
One example of a conveyor drive is disclosed in U.S. Pat. No. 4,222,481 to Dehne et al., hereby incorporated in its entirety by reference. With particular reference to
FIGS. 7 and 8
of this patent, pivotal movement of the floating frame is easily opposed by a compression spring. The compression spring is arranged between a plate attached to the moveable frame and another plate secured to the fixed frame. The force of the compression spring biases the movable frame against the torque caused by drive pull. The Dehne et al. patent also discloses a shock absorber to further restrain pivotal movement of the frame. The shock absorber is mounted in a similar fashion as the compression spring, the absorber being arranged between the floating frame and the fixed frame.
The Dehne et al. patent also teaches that a limit switch can be provided to provide overload protection in case of excessive pivotal movement of the floating frame, such caused by a chain jam or the like.
Another prior art conveyor drive is disclosed in FIG.
1
and designated by the reference numeral
10
., The drive is depicted in the same view as
FIG. 4
of the Dehne et al. patent. Shown is a reducer
1
, a reducer shaft
3
, a bearing
5
, and a drive sprocket
7
.
FIG. 1
does not show the caterpillar chain around the drive sprocket
7
.
FIG. 1
also shows an I-beam
9
which provides support for the trolley of a power and free system. The driven chain of the power and free system travels in a direction perpendicular to the view shown in FIG.
1
and in a direction from the motor (not shown) towards the reducer
1
.
The reducer
1
is also shown with an input shaft
11
and pulley
13
. The reducer
1
is connected to the motor via components
11
and
13
in a conventional fashion.
The speed reducer
1
is supported by a floating frame
15
, similar to the manner of support described in the Dehne et al. patent. The
FIG. 1
embodiment uses a torque arm assembly
17
and a compression screw
19
to monitor the chain pull on the conveyor drive. The torque arm assembly
17
includes a rod
18
, a compression spring
21
and a rod plate
25
. One end of the rod
18
is attached to the fixed frame
27
. The other end of the rod
18
is secured to the plate
25
. The spring
21
is interposed between the plate
25
and a bracket
23
attached to the floating frame
15
. In this configuration, the spring
21
biases the floating frame
15
in the direction A, in opposition to the drive torque occurring in the direction B.
The rod
18
has a strain gauge sensor
29
as a part thereof, the strain gauge sensor
29
monitoring the chain pull during conveyor operation. More particularly, the strain gauge sensor
29
is zeroed when the conveyor drive is at rest, i.e. zero chain pull. When the conveyor drive is operating and a drive torque B is applied to the floating frame
15
, the amount of chain pull is monitored for conveyor operation control.
Another embodiment similar to
FIG. 1
uses the torque arm assembly
17
without the strain gauge sensor
29
, thereby relying on other methods and techniques to monitor chain pull. One such technique uses a strain gauge link as part of the conveyor chain itself. The gauge on the link is calibrated so that the output of the gauge corresponds to the tension in the conveyor chain. The conveyor chain is stopped and the link is installed in the chain, the link then travelling around the conveyor system. Output data can be collected either by an umbilical cord and a data recorder or can be stored in computer memory for later download. Although the data collected in this fashion can be analyzed to find potential problem spots in the system, this method does not allow for the collection of data at one point in the conveyor system over a long period of time.
There are advantages to looking at the pull exerted by the drive over a period of time such as with the
FIG. 1
embodiment. One of the problems with this embodiment is that the strain gauge is incorporated into the drive frame. If the drive frame is redesigned for a new installation or use, the strain gauge must also be redesigned to fit the requirements of that particular drive. Alternatively, if the strain gauge is being added as a retrofit, an expensive and time consuming process is required to remove the torque arm and replace it with a strain gauge-containing torque arm assembly.
Consequently, a need has developed to provide simplified and improved methods and apparatus to monitor the chain pull in conveyor systems. The present invention solves this need by providing a simple but effective method to install a strain gauge on an existing conveyor as well as an improved conveyor drive apparatus. With the invention, the conveyor does not have to be stopped to install the strain gauge and must be stopped for just a short period of time for calibration.
SUMMARY OF THE INVENTION
Accordingly, it is a first object of the present invention to provide an improved chain tension monitoring apparatus.
Another object of the present invention is an apparatus for monitoring chain tension which is easily retrofitted on existing units.
A still further object of the present invention is a method and apparatus of monitoring chain tension using a force sensor that easily interfaces with a floating frame conveyor drive.
One other object of the present invention is a method and apparatus for monitoring chai
Carter Dan
Kubsik Robert
Dickinson Wright PLLC
Jervis B. Webb Company
Noori Max
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