Patent Grant
7454877
The present invention is directed to a strapping machine. More particularly, the present invention is directed to an improved tension control system for tensioning a strap around a load in a strapping machine.
Strapping machines are in widespread use for securing straps around loads. There are various types of strappers. One type of strapper is a stationary arrangement in which the strapper is stand-alone device that is part of an overall manufacturing of fabrication operation.
In a stand-alone strapper, a strapping head and drive mechanisms (feed and take-up) are typically mounted within a frame. A chute is likewise mounted to the frame, through which the strapping material is fed.
In one known configuration, a strapping head is mounted at about a work surface, and the chute is positioned above the work surface and above the strapping head. Strap material is fed to the strapping head, and is then driven by feed wheels (by a motor) to feed the strap materials through the strapping head and around the chute back to the strapping head. Once the strap material is fed back to the strapping head, a gripping arrangement grips the strap material and the same motor used to feed the strap material around the chute is reversed and the strap material is stripped from the chute and tensioned around the load. The tensioned strap is then gripped by a second part of the gripping arrangement and the motor is turned off. A cutter in the strapping head cuts the tensioned strap (from the source or supply) and the strapping head forms a seal in the strapping material, sealing the strapping material to itself around the bundled load.
Proper strap tension is achieved by various means. Tension can be controlled mechanically by the use of a mechanical clutch. Alternatively, tension can be controlled by varying the voltage to a drive clutch associated with the motor. When the tension applied to the strap overcomes the voltage being sent to the drive clutch, the clutch slips and continues to slip for a predetermined period of time. Once that time expires, tension is considered complete, whereupon the strap material is cut and the motor and clutch are turned off. However this can result in wear on the clutch, and variability in the tension applied to the strap material
Accordingly, there exists a need for a more effective and consistent method for tensioning strapping material around a load in a stationary strapper.
The present invention is a tension control system for a strapping machine configured to feed a strap around a load, position, tension and seal the strap material around the load. The tension control system includes a motor assembly, an adjustable speed drive and a controller.
The motor assembly is configured to convey the strap around a strap chute, retract the strap around the load, and tension the strap around the load. The adjustable speed drive includes inputs for receiving a first reference signal and a second reference signal. The adjustable speed drive is capable of actuating the motor assembly to apply a first amount of torque to the strap when receiving the first reference signal and to apply a second amount of torque to the strap when receiving the second reference signal.
The controller is configured to operate the adjustable speed drive in a first mode while conveying the strap around the strap chute and retracting the strap material around the load, and a second mode while tensioning the strap around the load. In the first mode, the adjustable speed drive actuate the motor assembly to apply the first amount of torque to the strap, and in the second mode, the adjustable speed drive actuates the motor assembly to apply the second amount of torque to the strap.
In another aspect, the present invention provides a method for tensioning a strap around a load in a strapping machine. The method includes actuating a motor assembly to apply a first amount of torque in a first direction to convey the strap around a strap chute, actuating the motor assembly to apply the first amount of torque in a second direction to retract the strap around the load, actuating the motor assembly to apply a second amount of torque in the second direction to tension the strap around the load, determining that the second amount of torque has been applied to the strap, and signaling the completion of tensioning to a controller.
These and other features and advantages of the present invention will be apparent from the following detailed description, in conjunction with the appended claims.
The benefits and advantages of the present invention will become more readily apparent to those of ordinary skill in the relevant art after reviewing the following detailed description and accompanying drawings, wherein:
While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred embodiment with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiment illustrated.
It should be further understood that the title of this specification, namely, “detailed Description of the Invention”, relates to a requirement of the United States Patent Office, and does not imply, nor should be inferred to limit the subject matter disclosed herein.
Referring to the figures, and in particular to
The strapping machine 100 includes a frame 102, a work surface 104, a strap chute 106, a strapping assembly 110, and a motor assembly 112. The strapping machine may also include a user control 114 to provide automatic operation and control of the strapping machine 100. A strap, indicated at 108 is illustrated diagrammatically in the chute 106.
As shown in
In one embodiment, the ASD 310 is a variable frequency drive designed to control the torque applied by the motor assembly 112 when tensioning the strap around the load. Generally, the ASD 310 receives AC power, converts the AC power to a DC intermediate power, and then converts the DC intermediate power to a quasi-sinusoidal AC power that is used to drive the motor assembly 112. In one exemplary embodiment, the ASD 310 may be an Allen Bradley PowerFlex 70® AC Drive, although it is understood that other commercially available ADSs may also be used.
The ASD 310 includes three power input terminals 312-316 for receiving a three-phase AC power signal 302 and three power output terminals 318-322 for outputting a three-phase quasi-sinusoidal AC power signal 304 to drive the motor assembly 110. While not shown in
The ASD 310 also includes a control terminal connected to the controller 370, a negative reference terminal 330, a positive reference terminal 332, and three terminals 324-328 used for selecting an input signal to be applied to the reference terminal 332. As will be discussed in more detail below, the amount of torque applied by the motor assembly 112 is controlled based on the signals received at the negative and positive reference terminals 330 and 332, and more particularly, by altering the voltage potential and/or current applied to the negative and positive terminals 330 and 332.
The ASD may also include a torque feedback input 334 operably connected to the motor assembly 112 for receiving a torque feedback signal 366 regarding the amount of torque being applied by the motor assembly 112 to the strap during tensioning.
The voltage divider 340 is preferably a three-terminal resistor (also referred to as a potentiometer) having a wiper 348 that is manually adjustable to different spots along the resistor. As the wiper 348 is adjusted, the resistance between the wiper 348 and one terminal 342 and 344 gets smaller while the resistance between the wiper and the other end gets larger. Accordingly, the wiper 348 can be adjusted to provide a specific attenuated voltage between a minimum voltage applied to one terminal and a maximum voltage applied to the other terminal.
In one embodiment, a first terminal 344 of the voltage divider 340 is connected to terminal 330 of the ASD 310, which is also preferably connected to a ground 352. A second terminal 342 of the voltage divider 340 is then connected to terminal 324 of the ASD 310, which is also connected to a reference voltage 354, for example 10V. A third terminal 346 of the voltage divider 340 is connected to the wiper 348 and to terminal 328 of the ASD 310.
A switch 350, such as, for example, a form C contact, may then be provided among terminals 324-328 of the ASD 310. The switch 350 is normally open between terminals 326 and 328, and normally closed between terminals 324 and 326. As a result, when not energized, the 10V reference voltage (i.e. the “maximum voltage”) at terminal 324 is applied to terminal 326 and in turn, terminal 332. When energized, the switch 350 becomes closed between terminals 326 and 328, and open between terminals 324 and 326. As a result, the attenuated voltage from the wiper 348, which is connected to terminal 328, is applied to terminal 326 and in turn, terminal 332.
The controller 370 is preferably a programmable logic controller configured to control the ASD 310. The controller 370 is also operably connected to the strapping assembly 110 to send and receive information and control signals to and from the strapping assembly. Although the controller 370 is illustrated as a separate unit from the ASD, the controller 370 may also be built-in or internal to the ASD. The controller 370 may also be comprised of several separate controllers.
The motor assembly 112 is driven by the three-phase power signal 304 output by the ASD 310, and is preferably comprised of an induction motor 362 and a tension clutch 364 that may be operably engageable with the motor 362. When actuated, the motor 362 drives a feed wheel, windless or similar apparatus in the strapping machine 100 to feed the strap 108 around the strap chute 106, take up the strap 108 around a load, and then tension the strap 108 around the load. The tension clutch 364 is preferably engaged only during the tensioning process.
While one specific embodiment of the tension control system is illustrated in
Various types of adjustable speed drives may also be used. The adjustable speed drive may have a single-phase input rather than a three-phase input, and may also be configured to drive other types of motors other than induction motors. The adjustable speed drive may also include additional terminals not illustrated in
Once the strap 108 is fed around the strap chute 106 and back into the strapping assembly 110, the strap 108 is gripped (step 406) and the ASD 310 is instructed by the controller 370 to operate in a reverse direction in the full-torque mode (step 408). The ASD 310 will continue to drive the motor assembly 112 in the full-torque mode until the strap 108 is taken up around the load. In one embodiment, the tension clutch 364 is not engaged during steps 404-408.
One the strap 108 is taken up around the load, the controller 370 instructs the ASD 310 to change from full-torque mode to a variable-torque mode (step 410). In the variable torque mode, the switch 350 is energized and therefore, the attenuated voltage set by the wiper 348 of the voltage divider 340 is supplied to the positive reference terminal 332 of the ASD 310. In step 412, the tension clutch 364 is engaged, and in step 414, the ASD 310 actuates the motor assembly 112, preferably in the reverse direction, to begin tensioning the strap 108 using an amount of torque set based on the attenuated voltage input to the positive reference terminal 332. It should be understood that since different embodiments and types of loads may require different amount of torque for sufficient tensioning, the attenuated voltage may be adjusted for each different embodiment or load.
In step 416, it is determined whether the torque output from the motor assembly 112 meets the desired torque set by the ASD 310. In one embodiment, this is accomplished by monitoring the torque applied by the motor assembly 112 using a sensor, or any other type of torque monitoring circuit. The motor assembly 112 may then be configured to either continuously transmit the torque feedback signal to the controller 370, or alternatively, to transmit the torque feedback signal to the controller 370 only upon the desired amount of torque being met.
If the motor output torque has not reached the desired torque, then the motor assembly 112 continues to tension the strap 108 around the load (step 418). If motor output torque has reached the desired torque, then a torque feedback signal 366 is transmitted from the motor assembly 112 to the ASD 310, informing the ASD 310 that the desired torque has been met (step 420). In step 422, the ASD 310 sends a signal to the controller 370 informing the controller that the tensioning process has been completed. In step 424, the controller 370 instructs the strapping assembly 110 to grip, seal, and cut the strap.
As a result of the aforementioned system and method, tensioning of the strap around the load in a strapping machine may be accomplished by adjusting the torque applied by the motor assembly and reporting back to the adjustable speed drive once the desired amount of torque has been achieved. Therefore, the tension clutch does not slip during tensioning.
In the present disclosure, the words “a” or “an” are to be taken to include both the singular and the plural. Conversely, any reference to plural items shall, where appropriate, include the singular.
From the foregoing it will be observed that numerous modifications and variations can be effectuated without departing from the true spirit and scope of the novel concepts of the present invention. It is to be understood that no limitation with respect to the specific embodiments illustrated is intended or should be inferred. The disclosure is intended to cover all such modifications as fall within the scope of the claims.
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| Number | Date | Country | |
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| 20080072539 A1 | Mar 2008 | US |
