The present disclosure is directed, in general, to tensioning of belts in machinery.
In moving belt systems it is important that belt tension be maintained in a desired range. If belt tension is too low, the belt may slip over pulleys. If belt tension is too high, excessive stress may be placed on pulleys, bearing and the belt.
Various disclosed embodiments include a system and method for tensioning a belt. An apparatus includes a fixed roller, rotatably coupled to a structure; a tensioning roller, rotatably coupled to a bracket; and a biasing device coupled to the structure and to the bracket. The bracket and the tensioning roller are coupled to the structure only by the biasing device and a belt passing around at least a part of the fixed roller and at least a part of the tensioning roller.
The foregoing has outlined rather broadly the features and technical advantages of the present disclosure so that those skilled in the art may better understand the detailed description that follows. Additional features and advantages of the disclosure will be described hereinafter that form the subject of the claims. Those skilled in the art will appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. Those skilled in the art will also realize that such equivalent constructions do not depart from the spirit and scope of the disclosure in its broadest form.
Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words or phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, whether such a device is implemented in hardware, firmware, software or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, and those of ordinary skill in the art will understand that such definitions apply in many, if not most, instances to prior as well as future uses of such defined words and phrases. While some terms may include a wide variety of embodiments, the appended claims may expressly limit these terms to specific embodiments.
For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, wherein like numbers designate like objects, and in which:
In a mechanical system that employs a belt—such as a conveyor belt or a power drive belt—belt tension is maintained within a desired range of value to ensure that the mechanical system does not malfunction. For example, if the belt tension drops too low, the belt may slip over a drive pulley, resulting in erratic motion of the belt. If the belt tension rises too high, the belt may place excessive forces on pulleys or rollers in the mechanism, causing the pulleys to bind and stop rolling.
Various methods and systems have been developed with the intention of applying a desired range of tensions to a belt. A tensioning roller may be mounted for motion relative to fixed rollers in the system and biased by a force away from the fixed rollers in order to tension a belt that passes over both the tensioning and fixed rollers. A tensioning roller may be positioned in a straight segment of the belt path and biased by a force in a direction orthogonal to the belt path in order to tension the belt. Typically, such a biasing force is supplied by a spring or a suspended dead weight and operates directly on the tensioning roller or an arm or plate to which the roller mounts. Such a tensioning roller is typically mounted to a base plate of the belt system by an arm, linear bearing, or other mechanism that supplies the biasing force and constrains motion of the tensioning roller. Such tensioning mechanisms may be complex, expensive, bulky, or affected by dynamic forces of the moving belt.
The floating roller 106 is rotatably mounted to a bracket 108, which is used to move the roller 106 to control the tension of the belt 102. As shown in
The biasing device 114 applies a force F1 to the tensioning cable 110, which operates to increase the tension in the belt 102. The bracket 108, acting under the tension of the belt 102, applies an opposing force F2 to the cable 110. When the force F1 exceeds the force F2 by an amount sufficient to overcome the capstan effect arising from the friction of the tensioning cable 110 passing around the fixed capstan 112, the tensioning cable 110 moves the bracket 108 and tensioning roller 106 in a direction to increase the tension in the belt 102 (to the left in
The bracket 108 and the tensioning roller 106 are coupled to the base plate 206 only by the cable 110 and the belt 102. Where the rollers 102, 104a and 104b are crowned rollers, the belt 102 is constrained from moving in the vertical direction in
The capstan effect of the tensioning cable 110 passing around the capstan 112 may be expressed as:
F
high
=F
low
*e
μΦ,
where e is the mathematical constant referred to as Euler's number, μ is the coefficient of friction between the tensioning cable 110 and the capstan 112, Φ is the number of turns of the tensioning cable 110 around the capstan 112 in radians, Fhigh is the larger of F1 and F2, and Flow is the smaller of F1 and F2. Where both the tensioning cable 110 and the capstan 112 are steel (as in the belt tensioning system 100), the value of μ is 0.8. Where the tensioning cable 110 wraps one-quarter turn around the capstan 112 (as in the belt tensioning system 100), the value of Φ is approximately 1.57. Thus for the tensioning cable 110 and the capstan 112 of the belt tensioning system 100, the value of eμΦ is approximately 3.5 and Fhigh=Flow*3.5. That is, if Fhigh exceeds Flow, by a factor of 3.5, the tensioning cable 110 will move around the capstan 112 in the direction of Fhigh. However, if Fhigh does not exceed Flow by at least a factor of 3.5, the tensioning cable 110 will not move around the capstan 112.
The tension of the belt 102 is depicted by the arrows labeled T in
In the belt tensioning system 100, a nominal value for the spring force, F1, is calculated as:
F
1=2*Tnominal*eμΦ−c,
where Tnominal and eμΦ are as described above and c is derived empirically to ensure that the belt 102 is not over-tensioned when T approaches Tlow.
In operation, when the belt 102 is powered off and T approaches the value Tlow, F2 may fall below F1 by more than the capstan effect factor, eμΦ, with the result that the tensioning cable 110 slips in the direction of F1. This slippage increases F2 until F2, aided by the capstan effect, is able to resist further slippage. In this way, the belt tensioning system 100 operates to prevent T from dropping below a specified minimum level. Subsequently, when the belt 102 is powered up and T rises from Tlow to the value Tnominal, the tensioning cable 110 does not slip unless F2 exceeds F1 by the capstan effect factor: i.e., unless T reaches 3.5*Tnominal. Such a high belt tension is not likely to occur in normal operation of a system where the belt tensioning system 100 is used.
Thus, the tensioning cable 110 may initially slip around the capstan 112 to adapt to a belt tension near Tlow. In this way, the belt tensioning system 100 establishes a minimum belt tension in the belt 102. However, once this initial adaptation has occurred, as the tension in the belt 102 rises, the belt tensioning system 100 remains rigid under the expected dynamic tension loads of the belt 102—that is, as long as the tension T remains within the expected range of Tlow to Tnominal. The belt tensioning system 100 has a flexible geometry that may be readily adapted to fir around other components of the belt-driven system. Furthermore, the belt tensioning system 100 has a smaller footprint, lower cost, and lower maintenance requirements than many other belt tensioning systems. The tensioning roller 106 is mounted to the floating bracket 108, rather than being mounted by a more complex and more expensive articulated mechanism to the base plate 206, as in some other belt tensioning mechanisms.
Similar to the belt tensioning system 100, in the belt tensioning system 300 a belt 302 passes over fixed rollers 304a and 304b and around a floating tensioning roller 306. The tensioning roller 306 is typically positioned just before a belt drive roller in the path of the belt 302—for example, fixed roller 304a or 304b, depending upon the direction of travel of the belt 302. The belt 302 extends from the tensioning system 300 into the rest of a larger mechanical system and may be travelling in either direction through the system.
The floating roller 306 is rotatably mounted to a bracket 308, which is used to move the roller 306 to control the tension of the belt 302. As shown in
Unlike the capstan 112 of the belt tensioning system 100, the one-way clutch roller 312 operates as a roller when the tensioning cable 310 is moving in the direction indicated by the arrow labeled F1 in FIG. 3—that is, in the counter-clockwise direction shown by the arrows on the roller 312. However, because of the action of its one-way clutch mechanism, the roller 312 acts as a capstan to resist motion of the tensioning cable 310 in the direction indicated by the arrow labeled F2.
The biasing device 314 applies a force F1 to the tensioning cable 310, which operates to increase the tension in the belt 302. The bracket 308, acting under the tension of the belt 302, applies an opposing force F2 to the tensioning cable 310. When the force F1 exceeds the force F2, the one-way clutch roller 312 rotates in the counter-clockwise direction, allowing the tensioning cable 310 to move the bracket 308 and tensioning roller 306 in a direction to increase the tension in the belt 302 (to the left in
However, because the roller 312 does not rotate in the clockwise direction, the roller acts as a capstan to resist motion of the tensioning cable 310 in the direction of F2. Thus, the force F2 must exceed the force F1 by an amount sufficient to overcome the capstan effect, in order for the tensioning cable 310, the bracket 308, and the tensioning roller 306 to move in the direction of F2, decreasing the tension in the belt 302.
The bracket 308 and the tensioning roller 306 are coupled to the base plate 406 only by the cable 310 and the belt 302. Where the rollers 302, 304a and 304b are crowned rollers, the belt 302 is constrained from moving in the vertical direction in
As described for the capstan 112, the capstan effect of the tensioning cable 310 passing around the one-way clutch roller 312 may be expressed as Fhigh=Flow*eμΦ. Because the roller 312 rotates in the counter-clockwise direction, the capstan effect only applies to motion in the direction of F2 and may be expressed as F2=F1*eμΦ. That is, F2 must exceed F1 by the factor eμΦ for the tensioning cable 310 to move in the direction of F2.
In the belt tensioning system 300, both the tensioning cable 310 and the capstan 312 are steel, and the value of μ is 0.8. Because the cable 310 wraps two full turns around the roller 312, the value of Φ is approximately 12.6. Thus, for the tensioning cable 310 and the roller 312, the value of eμΦ approximately 23,000 and F2=F1*23,000. That is, if F2 exceeds F1 by a factor of 23,000, the tensioning cable 310 will move around the capstan 312 in the direction of F2. However, if F2 does not exceed F1 by at least a factor of 23,000, the tensioning cable 310 will not move around the roller 312 in the direction of F2.
As described for the belt tensioning system 100, in the belt tensioning system 200, the tension T of the belt 102 is typically in a range from Tlow to Tnominal. Tlow typically occurs at startup and typically is established empirically. Tnominal is the nominal operating tension of the belt 102 and is set by the designer of the system in which the belt 102 is used.
In the belt tensioning system 300, a nominal value for the spring force, F1, is determined by:
F
1=2*Tlow,
where Tlow is as described above.
When T is at a low value, the biasing device 314 pulls the tensioning cable 310 counter-clockwise around the rotating one-way clutch roller 312, and the force F2 applied to the tensioning roller 306 is:
F
2
=F
1=2*Tlow.
In this way, the belt tensioning system 300 operates to prevent T from dropping below a specified minimum level.
However, as T rises above Tlow (and F2 rises above 2*Tlow) and the bracket 308 attempts to pull the cable 310 clockwise around the one-way clutch roller 312, the roller acts as a capstan, preventing the tensioning cable 310 from slipping around the roller 312 in the direction of F2 unless F2 rises above F1 by a factor of 23,000.
Thus, under normal running conditions, as T rises to Tnominal, the one-way clutch roller 312 resists turning and the force F2 applied to the tensioning roller 306 is:
F
2
=F
1+2*(Tnominal−Tlow), or
F
2=2*Tnominal.
That is, as T varies between Tlow and Tnominal, F2 varies between 2*Tlow and 2*Tnominal, because the one-way clutch roller 312 resists turning.
Thus, the tensioning cable 310 may be pulled initially around the rotating one-way clutch roller 312 to adapt to a belt tension near Tlow. However, once this initial adaptation has occurred, the belt tensioning system 300 remains rigid under the expected dynamic tension loads of the belt 302 within the expected range of range of values for T. Like the belt tensioning system 100, the belt tensioning system 300 has a flexible geometry that may be readily adapted to fir around other components of the belt-driven system. The belt tensioning system 300 also has a smaller footprint, lower cost, and lower maintenance requirements than many other belt tensioning systems. The tensioning roller 312 is mounted to the floating bracket 308, rather than being mounted by a more complex and more expensive articulated mechanism to the base plate 406, as in some other belt tensioning mechanisms.
Similar to the belt tensioning system 300, in the belt tensioning system 500 a belt 502 passes over fixed rollers 504a and 504b and around a floating tensioning roller 506. The tensioning roller 506 is typically positioned just before a belt drive roller in the path of the belt 502—for example, fixed roller 504a or 504b, depending upon the direction of travel of the belt 502. The belt 502 extends from the tensioning system 500 into the rest of a larger mechanical system and may be travelling in either direction through the system.
The floating roller 506 is rotatably mounted to a bracket 508, which is used to move the roller 506 to control the tension of the belt 502. As shown in
The biasing device 514 applies a force F1 to the tensioning roller 506, which operates to increase the tension in the belt 502. The bracket 508, acting under the tension of the belt 502, applies an opposing force F2 to the biasing device 514. When the force F1 exceeds the force F2, the bracket 508 and tensioning roller 506 move in a direction to increase the tension in the belt 502 (to the left in
The bracket 508 and the tensioning roller 506 are coupled to the base plate 406 only by the biasing device 514. Where the rollers 502, 504a and 504b are crowned rollers, the belt 502 is constrained from moving in the vertical direction in
As described for the belt tensioning system 300, in the belt tensioning system 500, the tension T of the belt 502 is typically in a range from Tlow to Tnominal. Tlow typically occurs at startup and typically is established empirically. Tnominal is the nominal operating tension of the belt 502 and is set by the designer of the system in which the belt 502 is used.
In the belt tensioning system 500, a nominal value for the spring force, F1, is determined by:
F
1=2*Tnominal,
where Tnominal is as described above. When T begins to fall below Tnominal, the tensioning roller 506 moves to the left to keep the belt tension at Tnominal. Similarly, when T begins to rise above Tnominal, the tensioning roller 506 moves to the right to keep the belt tension at Tnominal.
As such, the belt tensioning system 500 does not remain rigid under the dynamic tension loads of the belt 502. However, like the belt tensioning system 300, the belt tensioning system 500 has a flexible geometry that may be readily adapted to fir around other components of the belt-driven system. The belt tensioning system 500 also has a smaller footprint, lower cost, and lower maintenance requirements than many other belt tensioning systems. Also, the tensioning roller 512 is mounted to the floating bracket 508, rather than being mounted by a more complex and more expensive articulated mechanism to the base plate 606, as in some other belt tensioning mechanisms.
In some circumstances, a roller (for example, roller 504a) must be removed from a belt system utilizing a belt tensioning system according to this disclosure. Such circumstances might arise where an item being transported by the belt system becomes jammed and tension in the belt system must be temporarily reduced below Tlow in order to remove the jammed item. In such circumstances, the belt tensioning systems 100 and 300 will operate to pull the tensioning rollers 106 and 306, respectively, to increase tension in the belt to their respective minimum tensions. When the roller is replaced in the belt system, however, the capstan effect of the capstan 112 and the one-way clutch roller 312 will operate to prevent motion of the tensioning rollers 106 and 306, respectively, resulting in higher than expected tension in the belts 102 and 302. In belt systems where the need to remove a roller does not arise, or where operation of the belt tensioning system may be disabled while the roller is removed, the belt tensioning systems 100 and 300 provide the dual benefits of the ability to remain rigid under the expected dynamic tensioning loads of the belt being tensioned, as well as the reduced cost and mechanical simplicity of the floating tensioning roller. In belt systems where the need to remove a roller does arise and operation of the belt tensioning system cannot be disabled while the roller is removed, the belt tensioning system 500 provides the benefit of reduced cost and mechanical simplicity of the floating tensioning roller.
The conveyor belt 702a moves in a clockwise direction, driven by a drive roller 704a. The conveyor belt 702 passes, in turn, around idler rollers 704b, 704c, and 704d. The conveyor belt 702a includes a working section 706a, which is constrained by idler rollers 708. A return section 710 of the conveyor belt 702a is constrained by a single idler roller 712. The conveyor belt 702b moves in a counter-clockwise direction, but is otherwise similar to the belt 702a, being driven by a drive roller, having a working section 706b, passing around idler rollers, and being constrained by idler rollers 708b.
The conveyor belt system 700 is configured as a pinch drive system. That is, the working sections 706a and 706b are located adjacent to each other to form a gap 720, into which items may be introduced, to be “pinched” between the belts 702a and 702b and transported from the left end to the right of the conveyor belt system 700, as shown in
While the belt tensioning systems 550a and 550b are used in the pinch drive conveyor belt system 700, it will be understood that belt tensioning systems according to the disclosure may be used in any suitable belt system, including horizontal conveyor belts, power drive belts, manufacturing applications, food handling applications, and other moving belt systems.
Those skilled in the art will recognize that, for simplicity and clarity, the full structure and operation of all systems suitable for use with the present disclosure is not being depicted or described herein. Instead, only so much of the physical systems as is unique to the present disclosure or necessary for an understanding of the present disclosure is depicted and described. The remainder of the construction and operation of the systems disclosed herein may conform to any of the various current implementations and practices known in the art.
Although an exemplary embodiment of the present disclosure has been described in detail, those skilled in the art will understand that various changes, substitutions, variations, and improvements disclosed herein may be made without departing from the spirit and scope of the disclosure in its broadest form.
None of the description in the present application should be read as implying that any particular element, step, or function is an essential element which must be included in the claim scope: the scope of patented subject matter is defined only by the allowed claims. Moreover, none of these claims are intended to invoke paragraph six of 35 USC §112 unless the exact words “means for” are followed by a participle.
This application claims the benefit of the filing date of U.S. Provisional Patent Application 61/246,719, filed Sep. 29, 2009, and U.S. Provisional Patent Application 61/246,724, filed Sep. 29, 2009, both of which are hereby incorporated by reference.
Number | Date | Country | |
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61246719 | Sep 2009 | US | |
61246724 | Sep 2009 | US |