Methods and systems to facilitate spiral conveyance

According to a first aspect of the invention there is provided a conveyor system that includes a rotatably-mounted drum and a conveyor belt that is movable along a path that includes a helical portion around the drum. During movement of the conveyor belt, a surface of the drum frictionally engages an inside edge of the conveyor belt along the helical portion of the path. Finally, a peripheral surface of a rotating driving element directly engages the drum and to rotate the drum thereby operatively to move the conveyor belt along the path.

FIELD OF THE INVENTION

The present invention relates generally to the field of conveyer systems and, more specifically to capstan driven spiral conveyer systems.

BACKGROUND OF THE INVENTION

Capstan or low tension or drum spiral conveyors have been utilized in numerous industries for many years. Illustrated inFIG. 1is a schematic diagram of a drum spiral conveyor2, which is representative of those found in the prior art. The drum spiral conveyor2elevates or lowers items that rest on a conveyor belt that progress in a helical path around a drum. The conveyor belt is a closed loop that circulates up or down the drum over a conveyer bed that coils around the drum. The drum is usually driven by a chain that is driven by a gear motor and the belt is usually driven by a gear motor. The belt drive produces belt tension around the drum. The belt to drum frictional contact causes the belt to move up or down the helical slider bed in response to the drum slightly over-driving the belt speed. If the belt speed decreases relative to the drum speed, the belt may become slack on the drum thereby reducing the drum belt driving force. In contrast, an increase in the belt speed relative to the drum speed will increase the belt tension around the drum, which increases the drum belt driving force. As the conveyor belt moves along its path it carries items that rest upon the conveyor belt to a higher or lower level until the items exit the spiral conveyor at the desired destination. A number of operational problems are associated with driving the drum and detecting belt jams on the drum spiral conveyor.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a conveyor system. The conveyor system includes a rotatably-mounted drum; a conveyor belt that is movable along a path that includes a helical portion around the drum, during movement of the conveyor belt a surface of the drum frictionally engages an inside edge of the conveyor belt along the helical portion of the path; and a rotating driving element, a peripheral surface of the rotating driving element to directly engage the drum and to rotate the drum thereby operatively to move the conveyor belt along the path.

According to a second aspect of the invention there is provided a conveyor system. The conveyor system includes a rotatably-mounted drum without a center shaft; a conveyor belt that is movable in a path that includes a helical portion around the drum, during movement of the conveyor belt a surface of the drum frictionally engages an inside edge of the conveyor belt along the helical portion of the path; and a rotating driving element to directly engage the drum and to rotate the drum, thereby operatively to move the conveyor belt along the path.

According to a third aspect of the invention there is provided a method to monitor belt slack in a drum spiral conveyor. The method includes automatically measuring a first quantity of belt slack at a first time and a second quantity of belt slack at a second time; computing a change in belt slack based on the first quantity of belt slack and the second quantity of belt slack; and detecting if the change in belt slack exceeds a threshold.

According to a fourth aspect of the invention there is provided a method to monitor belt slack in a drum spiral conveyor. The method includes automatically measuring a first quantity of belt slack after a drum spiral conveyor has started; establishing a mid point of a comparison window based on the first quantity of belt slack, the comparison window including an upper limit and a lower limit; automatically measuring a second quantity of belt slack; and detecting if the second quantity of belt slack exceeds at least one of the upper and lower limit.

DETAILED DESCRIPTION

Driving the drum in a drum spiral conveyor poses a number of operational problems in the prior art. For example, one approach utilizes sprocket segments welded to the perimeter of the drum that are driven with a drive chain. This approach is associated with a number of disadvantages. One disadvantage of this approach is that the horizontal orientation of the drive chain requires sufficient drive chain tension to counteract the force of gravity which tends to de-rail the chain from the sprocket segments. Maintaining the proper drive chain tension requires repeated manual tension adjustments or the use of an automatic chain take-up or tensioning system. A second disadvantage of this approach is that a person in the vicinity of the spiral drum conveyor must be cognizant of safety hazards created by pinch points where the chain engages the gear motor sprocket and the drum sprocket segments. A third disadvantage of this approach is that the external frame and drum must be constructed with sufficient strength to withstand the horizontal force necessary to drive the drum in a circular motion. To this end, the drum may require a center shaft and internal structure to support the drum and transmit the drive torque to the other parts of the drum. Another approach to driving the drum utilizes a chain driven drive sprocket that is located below or above the drum. This approach addresses the safety issue presented above; however, it may have the disadvantage of requiring a large reduction gearbox, which greatly increases the cost of the gear motor assembly. Further, this approach is associated with high maintenance costs because the large reduction gearbox is often difficult to access.

Detecting and responding to belt jams in a drum spiral conveyor also pose operational problems. For example,FIG. 1illustrates one approach utilized by the drum spiral conveyors2that are found in the prior art. The drum spiral conveyor2utilizes two sensing devices that are respectively positioned at an upper boundary4and a lower boundary6. The sensing device positioned at the upper boundary4detects whether a take-up or tensioning roller8, that moves up and down in response the available slack in the belt, crosses the upper boundary4and the sensing device positioned at the lower boundary6detects whether the take-up roller8crosses the lower boundary6. Crossing a boundary indicates that belt movement has been disturbed (e.g., due to a mechanical drag, jam, etc.) thereby resulting in a belt crash (e.g., the belt has flipped up and no longer rests on the spiral conveyor bed). In response, the drum spiral conveyor shuts down to prevent the belt from breaking or flipping up in additional locations. This approach has a number of disadvantages. One disadvantage is that crashes are not prevented but merely identified. Attempts to prevent crashes have been made by lowering the upper boundary4and raising the lower boundary6; however, such attempts tend to increase the number of false failures (e.g., the conveyor shuts down prematurely). Another disadvantage of defining upper and lower boundaries is that the boundaries may be set too far apart which may result in a broken belt. Defining the proper boundary settings is also complicated by changes in belt length due to natural causes. For example, the belt may lengthen over time due to natural wear or the belt may lengthen due to a rise in ambient temperature or the belt may shorten due to a fall in ambient temperature. Another approach to responding to belt jams in a drum spiral conveyor has been to install flip-up sensors on the conveyor bed that may detect a belt flip up and trigger the drum spiral conveyor to shut down.

According to one aspect of the present invention there is provided a conveyor system that utilizes the peripheral surfaces of rollers to frictionally engage the bottom surface of the drum. The rollers provide surfaces on which the weight of the drum rests and rotate to drive the drum, thereby operatively moving a conveyor belt in a spiral path.

According to a second aspect of the present invention there is provided a conveyor system with a drum that is shaftless.

According to a third aspect of the present invention there is provided a method to detect if the amount of slack in a conveyor belt for a drum spiral conveyor system exceeds an upper or lower limit. The method utilizes a sensing device that measures the amount of slack in a conveyor belt at a predetermined period after the drum spiral conveyor has started. The amount of measured slack is used to establish a midpoint of a comparison window that includes an upper limit and a lower limit. During normal operations the amount of slack in the conveyor belt is measured with the sensing device and compared against the upper limit and the lower limit. If the method detects that the amount of slack in the conveyor belt exceeds the upper limit or the lower limit then an action may be initiated.

According to a fourth aspect of the present invention there is provided a method to detect if a change in the amount of slack in a conveyor belt on a spiral conveyor system exceeds a threshold. The method utilizes a sensing device to measure the amount of slack in the conveyor belt. After a configurable period of time, the sensing device is again utilized to measure the amount of slack in the conveyor belt. A change in belt slack is computed. If the method detects a change in belt slack that exceed a threshold then an action may be initiated.

FIG. 2is a drawing illustrating a drum spiral conveyor10, according to an exemplary embodiment of the invention. The drum spiral conveyor10includes of an external frame12, a rotatably mounted drum14, a conveyor belt26, rotating driving elements in the form of rollers28, a roller gear motor30, a belt gear motor34, a take-up or tensioning tower36and a control unit70.

The external frame12includes a base frame16, horizontal support bars20, vertical support columns22, and a top frame24. The base frame16rests on a support surface (e.g., the ground) and is fastened to the vertical support columns22which, in turn, are fastened to the top frame24. The horizontal support bars20support a helical slider bed18that commences at a lower tail section31, then wraps or spirals around the drum14, and exits into an upper belt drive section25. A positive slope of the helical slider bed18elevates the belt26as it progresses. Each 360° traveled by the belt26may be referred to as a wrap. The vertical distance between wraps may be referred to as rise. For the elevating example, the upper belt drive section25is positioned to receive the belt tangentially from the drum14.

The external frame12may be relatively light compared with external frames found in the prior art systems. Indeed, the external frame12(e.g., top frame24, vertical support columns22, horizontal tubes20, and base frame16) may be substantially stabilized by the drum14and may function to primarily support and stabilize the helical slider bed18. This contrasts with external frames for drum driven spiral conveyer systems found in the prior art that must support the weight of the drum and the loads that are generated to rotate the drum.

The belt26wraps around the drum14and may be supported by the helical slider bed18, as described above. An ascending belt26may exit the helical slider bed18onto the upper belt drive section25pass through a take-up tower36and return to the helical slider bed18via the lower tail section31. The belt26is fed tangentially to the surface of the drum14by properly positioning the lower tail section31. The belt26is endless and may be side-flexing. In addition, the belt26may be fabricated from any suitable material(s) (e.g., steel, plastics, etc.) and driven by the belt gear motor34that is positioned in the upper belt drive section25and controlled via the control unit70. Other embodiments may drive the belt26by positioning the belt gear motor34in other locations along the path of the belt26.

The take-up tower36may function as a belt reservoir to accommodate changes in the length of the belt26. For example, the length of the belt26may increase with use (e.g., pin and link wear). Consequently, a belt26that is old may require the take-up tower36to store or retain a greater amount of belt26than a belt26that is new. In addition, the length of the belt26may also be affected by temperature. For example, the length of the belt26tends to increase in response to warmer temperatures and to decrease in response to cooler temperatures. Inasmuch as the spiral conveyor10may be utilized in summer/winter ambient conditions and warm or cool working environments (e.g., freezing, cooking, etc.) then the length of the belt26that is stored in the take-up tower36may be observed to change according to use. Thus, not only may the age of the belt26determine its length but also the working environment in which the drum spiral conveyor10is deployed. Also, the length of the belt26may vary during operation of the spiral conveyor10with regard to the amount of tension that is applied to the belt26. For example, an increase in tension on the belt26may stretch the belt26which may minimize the length of belt26around the drum14and result in a greater quantity of the belt26in the take-up tower36. Conversely, if tension on the belt26is reduced then additional belt may be removed from the take-up tower36to wrap around the drum14. In addition, the amount of drum over-drive and product loading may effect belt tension. Thus, the tower36may release and hold portions of the belt26so that an appropriate portion of the belt26extends along the helical slider bed18.

The drum14rotates on a vertical axis and frictionally engages the side of the belt26. The drum14pushes the belt26and consequently tends to compress the belt as it rotates. The drum14may vary in diameter and height in different embodiments. In one embodiment the outside cylindrical surface of the drum14may be solid and defined by stainless steel panels. Other embodiments may utilize closely spaced bars to form the surface of the drum14.

Rollers28may be positioned under the drum14. The rollers28support the weight of the drum14and directly engage the bottom surface of the drum14to rotate the drum14. Each roller28may be an idler roller or driven by a roller gear motor30that may be controlled by the control unit70.

Exemplary Operation of Drum Spiral Conveyor

The drum spiral conveyor10generally operates as follows. The control unit70initially signals the roller gear motors30to drive the rollers38, which in turn, drive the bottom surface of the drum14to rotate the drum14. Next, the control unit70signals the belt gear motor34to pull the belt26taught thereby producing belt tension around the drum14that, in turn, causes the surface of the drum14to frictionally engage an inside edge of the belt26. The frictional contact between the belt26and drum14may cause the belt26to move up or down the slider bed18, depending on the direction of the rotation of the drum14. The belt26moves as the drum14slightly overdrives the belt26(e.g., the belt26moves at a slower speed than the drum14). If the belt gear motor34decreases belt speed, the belt26may become slack on the drum14thereby reducing the frictional contact between the drum14and the belt26, which in turn, reduces the driving force of the drum14. This may result in a reduction of the amount of belt in the take-up tower36. On the other hand if the belt gear motor34increases belt speed, the belt26may become taught around the drum14thereby increasing the frictional contact between the drum14and the belt26, which in turn, increases the driving force of the drum14and may result in an increase in the amount of belt in the take-up tower36.

FIG. 3Ashows a top view37andFIG. 3Bshow a side view39of the drum spiral conveyor10, according to one embodiment. The top view37illustrates the upper belt drive section25and the lower tail section31as straight projections from the external frame12and the drum14.

FIG. 4Aillustrates an exemplary embodiment of the drum14with cut away drum panels. The drum14may be seated on a drum base50which, in turn, is seated on the lower base frame16, according to one embodiment. One or more drum panels54may be bolted to the drum base50although other embodiments may utilize vertical bars in place of the drum panels54. A top frame24holds the drum panels54in place. The drum14may be without a center shaft (e.g., shaftless), as may be viewed in the upper portion of the drum14where the drum panels54are illustrated as cut away. In contrast, drums found in the prior art require a center shaft that extends axially through the drum as well as other supporting structure. For example, drums in the prior art require significant inner structure, a center shaft, and bearings at the top and bottom. The bearings must be mounted to a fixed external frame with sufficient integrity to hold the vertical orientation of the drum. Further, drum spiral conveyors in the prior art require an external frame of sufficient integrity to absorb the horizontal load required to keep the drum vertical. In contrast, the shaftless drum14is held in a vertical position by rollers28which are supported by the support surface or floor with structural loading that is perpendicular to the floor and with reduced horizontal loads imparted to the external frame.

FIG. 4Billustrates a shaftless drum base50mounted on top of a centering stub shaft40with bearings that provide a positive means of fixing the center of rotation for the drum14, according to one embodiment.

FIG. 5Aillustrates a roller assembly53, according to one embodiment. The roller assembly53may include the roller28, a shaft42, roller bearings46, a roller mounting plate48and an optional roller gear motor30. The roller28may be centered on the shaft42with roller bearings46of a pillow block style. The roller bearings46, in turn, mount to the roller mounting plate48. Each roller assembly53may include a roller gear motor30that may drive the respective roller28, according to an embodiment. The roller gear motor30may be controlled via the control unit70. One embodiment utilizes a hollow shaft gear motor to drive the roller28. Another embodiment may utilize a conventional sprocket and chain drive to drive the roller.

FIG. 5Afurther illustrates the roller28with a taper44, according to one embodiment. The roller28includes the taper44to maintain the same instantaneous velocity at all contact points between the peripheral surface of the roller and the bottom surface of the drum14. The specific amount of taper44corresponds to a diameter of the drum14and may be computed to maximize the contact between the roller28and the bottom surface of the drum14. An exact diameter may be required at each end of the roller28to reduce wear on a (non-driven) roller28that is idle (e.g., a roller that is not driven by the roller gear motor30) and to prevent skidding and/or maximize drive friction on a roller28that is utilized to drive (e.g., a roller that is driven by the roller gear motor30) the bottom surface of the drum14.

FIG. 5Billustrates the roller28as positioned to drive the bottom surface of the drum14, according to one embodiment. The roller28includes a peripheral surface55(e.g., outside surface) that frictionally engages the bottom surface of the drum14to rotate the shaftless drum14. Other embodiments may utilize the peripheral surface55of a sprocket or some other rotating driving element. For example, a sprocket may utilize a mesh to engage a surface of the shaftless drum14. The peripheral surface of the roller28or sprocket may be contrasted with mechanisms found in the prior art that utilize an inside surface to pull a drum (e.g., a chain). It will be appreciated that other embodiments may utilize the roller28to drive other surfaces of the drum (e.g., outside top surface, outside cylinder surface, inside bottom surface, inside top surface, inside cylinder surface, etc.).

The roller28may be fabricated out of steel. The outer surface of the roller28may be vulcanized with polyurethane for greater friction with the drum14, although other embodiments may utilize other materials for fabrication and drum engagement.

One potential advantage of driving the shaftless drum14with the roller28is the mitigation of the need for a special, heavy and/or costly “large ratio” gear motor. For example, the diameter of the roller relative to the diameter of the drum14provides a large ratio (e.g., many revolutions of each roller per single revolution of the drum) that enables the use of a gear motor with a gear motor ratio that is used in straight running mechanical conveyor applications. Thus, in one exemplary embodiment, a direct benefit in the form of economical and readily available gear motors may be realized by utilizing the roller(s)28to drive the drum.

FIG. 5Dillustrates a rotating driving element that includes a sprocket332driven by a roller gear motor30, according to one embodiment. The sprocket332is further shown to directly engage the drum with a meshed engagement332.

FIG. 5Eillustrates a rotating driving element directly engaging an outside top surface of a drum, according to one embodiment. The rotating driving element includes a roller28driven by a roller gear motor30. Also illustrated are idler rollers supporting the bottom of the drum14.

FIG. 5Fillustrates a rotating driving element directly engaging an outside cylindrical surface of a drum14, according to one embodiment. The rotating driving element includes a roller28driven by a roller gear motor30. Also illustrated are idler rollers supporting the bottom of the drum14.

Thus, broadly, a shaftless drum for a spiral drum conveyor may be driven by the surface of a roller thereby obviating the need to utilize a chain to drive the drum. Advantages of this approach may include elimination of maintenance costs associated with a chain (e.g., ensuring proper chain tension), increased safety due to pinch points caused by a chain, elimination of the shaft of the drum, elimination of substantial portions of the inner supporting structure of the drum, and elimination of a costly gearbox.

FIG. 6is a block diagram illustrating a drum spiral conveyor10in relation to a control unit70, according to one exemplary embodiment. The control unit70includes a control panel74and a fault detection machine76. In one exemplary embodiment the fault detection machine76is a computer that receives communications from a sensor72, processes the communications with fault detection module(s)82and responds to a detected fault by speeding up or slowing down a roller gear motor30, speeding up or slowing down a belt gear motor34, or stopping the drum spiral conveyor10. The fault detection module(s)82include a compute module84and a processing module86.

The sensor72may utilize laser technology to continuously detect the position of a take-up roller35. The sensor72includes a laser that emits a laser (or light) beam which bounces off reflector tape88that is attached to the take-up roller and is sensed by the sensor72. For example, one embodiment may include the Banner Laser Distance Eye, manufactured by Banner Engineering Corporation of Minneapolis, Minn. Other embodiments may utilize sonic, LED, mechanical spring loaded wire/encoder, photoelectric or another technology to measure the position of the take-up roller35.

The control panel74includes, for example, an emergency stop button90to make an emergency stop of the drum spiral conveyor10, a reset button92to reset the drum spiral conveyor10, start button96, a stop button98, a manual drum jog102, a manual/automatic selector104to manually or automatically operate the drum spiral conveyor10, and a manual belt jog106.

Exemplary Measuring of the Position of the Take-Up Roller

The control unit70utilizes the sensor72to monitor the position of a take-up roller35in the take-up tower36. An arrow71illustrates that the take-up roller35may elevate or lower depending on the amount of slack in a belt26. An increase in slack in the belt may cause the take-up roller35to lower (e.g., the amount of belt entering the take-up tower36is greater than the amount of belt leaving the take-up tower36). On the other hand, a decrease in slack in the belt26may cause the take-up roller35to elevate or rise (e.g., the amount of belt entering the take-up tower36is less than the amount of belt leaving the take-up tower36). An increase in slack may be caused by starting the drum spiral conveyor10, normal belt wear, a temperature increase, etc. A decrease in slack may be caused by starting the drum spiral conveyor10, a temperature decrease, etc. An increase or decrease in slack may also be caused by sudden jamming of the belt, overloading of the belt, etc.

FIG. 7is a diagram illustrating a method120, according to one embodiment, to detect if a change in belt slack on a spiral drum conveyor exceeds a threshold. The method120is illustrated by means of a Cartesian plane with an x axis corresponding to time and a y axis corresponding to the position of the take-up roller35(e.g., slack in belt). The x axis identifies two configurable periods of time including a startup delay122and a sample period124. The startup delay122is a period that must expire before utilizing the sensor72to measure a first quantity that quantifies the position of the take-up roller35. The sample period124is the amount of time that must elapse between measuring the first quantity and a second quantity. The method120is utilized to compute a change in the belt slack based on the first quantity of belt slack and the second quantity of belt slack. Note that an absolute value of the change in belt slack is computed as denoted by the brackets. Thus, a positive or negative change in belt slack (e.g., a rising or falling slope) may be compared with a threshold132to determine if the change in belt slack exceeds a threshold for the configured sample period124.

FIG. 8is a block diagram illustrating a method140, according to one embodiment, to detect if a change in belt slack on a spiral drum conveyor exceeds a threshold. Referring toFIG. 7andFIG. 8the method140commences at operation142where the fault detection machine76waits until the startup delay122has expired. The startup delay122is a configurable value and may be adjusted to accommodate changes in the configuration of the drum spiral conveyor10(e.g., adding or removing wraps, changing belts, reversing direction, etc.).

At operation144, the fault detection machine76signals the sensor72to automatically measure a first quantity of belt slack by sensing the position of the take-up roller35. Next, the sensor72communicates the first quantity to the compute module84at the fault detection machine76. At the fault detection machine76, the compute module84stores the first quantity in a register.

At operation146, the fault detection machine76waits until the sample period124has elapsed. The sample period124is a configurable value and may be adjusted to detect various conditions that are exhibited by the drum spiral conveyor10.

At operation148, the fault detection machine76signals the sensor72to automatically measure a second quantity of belt slack by sensing the position of the take-up roller35. Next, the sensor72communicates the second quantity to the compute module84at fault detection machine76. At the fault machine76, the compute module84stores the second quantity in a register.

At operation150, the compute module84computes a change in belt slack. The compute module84computes the change in belt slack by subtracting the second quantity from the first quantity and taking the absolute value of the result.

At decision operation152, the processing module86detects if the absolute value of the change in belt slack is greater than a configurable threshold132. If the absolute value of the change in belt slack is greater than the configurable threshold132then a branch is made to operation154. Otherwise a branch is made to operation144.

At operation154, the processing module86initiates an action. For example, the processing module86may stop the drum spiral conveyor10by stopping the belt gear motor34and the roller gear motors30. In another embodiment the processing module86may adjust the ratio of the speeds of the belt gear motor34to the roller gear motors30. Indeed, the speeds of the belt gear motor34and the roller gear motors30may be respectively increased or decreased to appropriately respond. It will also be appreciated that multiple thresholds132may be processed concurrently; each threshold132associated with a corresponding sample period124and a corresponding action. For example, the threshold132may be low and the sample period174may be short to detect a sudden jam or stopping condition. In response to this condition, the processing module86may stop the belt gear motor34and the roller gear motors30to prevent the belt26from flipping up (e.g. a crash) and damaging products. In addition, a second threshold132may be high and the corresponding sample period124may be long to detect a slow overloading condition or an unfavorable overloading of the belt26. In response to these conditions, the processing module86may increase the drum speed by increasing the roller gear motors33until a maximum overdrive speed is reached. Indeed, the fault detection machine76enables continuous monitoring of the take-up roller35to acquire information that is used to characterize various conditions on the drum spiral conveyor10. The acquired information may subsequently be used to configure an appropriate threshold132, sample period124, and action.

Thus, broadly speaking a method to detect if a change in belt slack on a spiral drum conveyor10exceeds a threshold has been described. Advantages of this approach may include detecting an unfavorable condition before a belt crash occurs, elimination of flip-up sensors on the helical slider bed18because a unfavorable condition is detected before a belt crash occurs, and acquiring information to configure various sets of thresholds132, sample periods174and actions to detect and mitigate or eliminate operational problems.

FIG. 9is a diagram illustrating a method150, according to one exemplary embodiment, to detect if belt slack on a spiral drum conveyor exceeds an upper or lower limit. The method150is illustrated by means of a Cartesian plane with an x axis corresponding to time and a y axis corresponding to the position of the take-up roller35(e.g., slack in belt). The x axis includes a startup delay152which may be a configurable period of time. The startup delay152is a period that must expire before utilizing the sensor72to measure a position of the take-up roller35that will be utilized to establish a midpoint154of a comparison window156. Extending a configurable distance from the midpoint154is an upper limit158and a lower limit160. During normal run operations, the method150is utilized to detect if the belt slack, as measured with the sensor72, is greater than the upper limit158or less than the lower limit160.

FIG. 10is a block diagram illustrating a method170, according to one embodiment, to detect if belt slack on a spiral drum conveyor (e.g., the drum conveyor10) exceeds an upper or lower limit. Referring toFIGS. 9 and 10the method170commences at operation172where the drum spiral conveyor10starts.

At operation174, the fault detection machine76waits until the startup delay152has expired. The startup delay152is a configurable value and may be adjusted to accommodate changes in the configuration of the drum spiral conveyor10(e.g., adding or removing wraps, changing belts, reversing direction, etc.).

At operation176, the fault detection machine76signals the sensor72to automatically measure a first quantity of belt slack by sensing the position of the take-up roller35. Next, the sensor72communicates the first quantity to the compute module84at fault detection machine76. At the fault detection machine76, the compute module84stores the first quantity in a register.

At operation178, the compute module84establishes the midpoint154of the comparison window154based on the first quantity and computes an upper limit158and a lower limit160by adding respective configurable values to the midpoint154.

At operation180, the fault detection machine76signals the sensor72to automatically measure a second quantity of belt slack by sensing the position of the take-up roller35. Next, the sensor72communicates the second quantity to the compute module84at the fault detection machine76. At the fault machine76, the compute module84stores the second quantity128in a register.

At decision operation182, the processing module86detects if the second quantity is greater than the upper limit158. If the second quantity is greater than the upper limit158then a branch is made to operation184. Otherwise a branch is made to decision operation186.

At decision operation186, the processing module86determines if the second quantity is less than the lower limit160. If the second quantity is less than the lower limit160then a branch is made to operation184. Otherwise a branch is made to operation186.

At operation184, the processing module86initiates an action and processing continues at operation188. For example, the processing module86may stop the drum spiral conveyor10by stopping the belt gear motor34and the roller gear motors30. In another embodiment the processing module86may initiate an action to recover, as described above.

At operation188, the fault detection machine76waits a configurable period of time.

Thus, broadly speaking a method to detect if belt slack on a spiral drum conveyor exceeds an upper or lower limit has been described. Advantages of this approach may include detecting that a limit has been exceeded before a belt crash occurs, elimination of flip-up sensors on the helical slider bed18because a unfavorable condition is detected before a belt crash occurs, and automatically establishing and utilizing upper and lower limits to filter out changes in belt length that are naturally caused.

The exemplary computer system300includes a processor302(e.g., a central processing unit (CPU) a graphics processing unit (GPU) or both), a main memory304and a static memory306, which communicate with each other via a bus308. The computer system300may further include a video display unit310(e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)). The computer system300also includes an alpha-numeric input device312(e.g., a keyboard), a cursor control device314(e.g., a mouse), a disk drive unit316, a signal generation device318(e.g., a speaker) and a network interface device320.

The disk drive unit316includes a machine-readable medium322on which is stored one or more sets of instructions (e.g., software324) embodying any one or more of the methodologies or functions described herein. The software324may also reside, completely or at least partially, within the main memory304and/or within the processor302during execution thereof by the computer system300, the main memory304and the processor302also constituting machine-readable media.

The software324may further be transmitted or received over a network326via the network interface device320.