HK1168831B - A device and method for detecting a missing step of a conveyor - Google Patents

Description

Apparatus and method for detecting a missing step of a conveyor

Technical Field

The present disclosure relates generally to safety control systems for conveyors and, more particularly, to an apparatus and method for detecting a missing step of a conveyor.

Background

Conveyors, such as escalators, moving walkways, and the like, provide a moving path for quickly and conveniently transporting people from one location to another. More specifically, the moving pallets or steps of the conveyor move passengers between two landings at a predetermined rate along the length of the path. Step chains, hidden and disposed below the conveyor, are used to interconnect the steps in a closed loop fashion. The step chain moves the steps along the exposed upper surface of the conveyor, under the drive of the main drive source, drive shaft, and associated sprockets, to transport passengers between landings. Sprockets provided in each of the two landings guide the step chain through an arc to reverse the direction of step movement and form a cyclic return path.

Because of their continuous motion, conveyors are prone to various internal malfunctions that may cause further injury to passengers on or near the conveyor. One of these failures pertains to misalignment or drop-out of the pallet or step. Over time, one or more steps of the conveyor may break loose from the associated step chain, causing the step to drop or fall undetected into the conveyor system. A missing step may also result from improper maintenance. The conveyor requires regular maintenance during which one or more steps may be removed, replaced, etc. However, if the steps are not properly fastened or realigned with the step chains, the steps may break loose and fall. In any event, if the control system of the conveyor fails to detect a gap caused by a missing step, the conveyor may continue to operate, advancing the gap to the upper surface of the conveyor and exposing the gap to passengers. An uninspected passenger may fall or step into the void and be injured. The problem of missed pallets or steps and their detection is therefore well known in the conveyor art. While there are several existing systems that provide such safety control measures for conveyors and aim to accurately detect such faults, they have their drawbacks.

Safety control systems for conveyors exist in which electromechanical switches are used to detect steps or their absence. Such systems position an electromechanical switch within the return path of the conveyor in order to detect misaligned or unsupported steps. Due to gravity, an unsupported step in the return path may swing or hang from the step chain and place the step directly in the path of the electromechanical switch. However, such electromechanical switches do not function properly if the steps are either misaligned entirely or disengaged entirely from the step chain. In addition, such electromechanical switches are significantly more prone to wear and are unreliable.

Other missing step detection systems employ photoelectric sensors that use light or its interruptions to monitor the steps of the conveyor. In such systems, it is desirable for each step of the conveyor to have a through hole that passes completely through the width of the step. When the steps are properly aligned and supported by the step chain, the photo-beam is aligned to pass directly through the holes of the steps. If the steps are misaligned, the beam is interrupted and the control system responds to the error. One disadvantage of such mechanisms is that the individual steps need to be changed greatly to accommodate such photosensors and therefore cannot be retrofitted to conveyors carrying steps without through holes. Furthermore, safety control systems for conveyors using photoelectric sensors are susceptible to dust, debris, or anything else that may be present or may collect in the through-hole over time and obstruct the light path.

Yet another existing missing step detection system employs proximity sensors that continuously detect the presence of each passing step in the return path. Such sensors electromagnetically interact with metal in the passing steps, outputting corresponding voltages or currents indicative of the presence or absence of the passing steps. However, in the case of steps modified for plastic or rubber inserts, there is not enough metal to be accurately and reliably detected by the sensor. Typically, conveyor safety control systems using proximity sensors require significant modifications to the configuration of the steps. Some proximity sensor driven safety control systems may require the top surface of the steps to be aligned in a linear fashion with the return path. Other systems may require the sides of the steps to be linear or flat.

More common proximity sensors for detecting a missing step are capacitive sensors and inductive sensors. Capacitive sensors continuously measure the voltage difference or the electric field created by the sensor itself. When in close proximity to the sensor, the metal passing through the steps deflects the electric field, creating a voltage difference and causing the sensor to output a signal corresponding to the change in the electric field. However, capacitive sensors are susceptible to sources other than the metal passing through the steps, such as dust, dirt, or even humidity in the air, and therefore the electrical signal output by the capacitive sensor is often unreliable.

Many systems also employ inductive proximity sensors, which are durable and more reliable than capacitive sensors. Inductive sensors continuously monitor the level of current flowing through an inductive coil within the sensor. When in close proximity to the sensor, the metal passing through the steps significantly alters the current in the induction coil and causes the sensor to output a signal corresponding to the change in inductance. As with capacitive sensors, inductive sensors output a continuous signal, which requires an associated control system to monitor the continuous signal output by the capacitive or inductive sensor. However, according to new standards and safety regulations for conveyor systems, safety control systems monitoring continuous signals must also incorporate expensive certified sensors that measure the integrity of the proximity sensors.

In addition, missing step detection systems that use proximity sensors and rely on continuous signal output rely on parameters that are not fixed or constant, such as conveyor speed and time. For example, using the speed of the conveyor as a frame of reference, the system proposes an expected time window or window during which the next successive step is detected by the proximity sensor. From a signal processing point of view, the proximity sensor outputs a continuous detection signal, and the expected window is rather broad and ambiguous. This makes it more difficult for the control system to accurately filter unwanted noise from the desired detection signal and make accurate decisions based on the filtered signal. Furthermore, while this method may be effective when the conveyor is moving at a constant speed, it is unreliable when the conveyor is accelerating, decelerating, opening or closing.

Accordingly, there is a need for a robust safety control system that accurately, reliably, and cost-effectively detects misaligned or missing steps while fully meeting current safety standards and regulations. More specifically, there is a need for a missing step detection system for a conveyor that does not require expensive authentication sensors, is redundant, or provides its own self-test. Further, there is a need for a missing step detection system that provides alternating output signals with less noise and correlates the sensor output signals to produce a fixed reference value that is independent of conveyor speed and time.

Disclosure of Invention

According to one aspect of the present disclosure, an apparatus for detecting a missing step or misaligned step of a conveyor extending between a first platform and a second platform is provided. The apparatus includes at least one driving speed sensor configured to detect a driving speed and output a driving pulse signal corresponding to the driving speed; at least one first step sensor configured to detect each step at the first platform and output a first step pulse signal corresponding to the step at the first platform, and at least one second step sensor configured to detect each step at the second platform and output a second step pulse signal corresponding to the step at the second platform; and a control unit receiving the drive pulse signal and the first and second step pulse signals, the control unit being arranged to determine a frequency of the drive pulse signal, determine a drive pulse ratio per step pitch, determine a phase difference between the first and second step pulse signals, monitor changes in the drive pulse ratio per step pitch and the step pulse signal phase difference, and provide instructions to adjust operation of the conveyor in response to the detected changes.

According to another aspect of the present disclosure, a method is provided for detecting a missing step or a misaligned step of a conveyor extending between a first platform and a second platform. The method comprises the following steps: determining a drive pulse signal corresponding to the conveyor speed; determining a first step pulse signal corresponding to a step at a first platform; determining a second step pulse signal corresponding to a step at a second platform; determining a drive pulse ratio per step pitch; determining a phase difference between the first and second step pulse signals; monitoring the variation of the drive pulse ratio and the step pulse signal phase difference of each step interval; and providing instructions to adjust operation of the conveyor in response to the detected change.

These and other aspects of the disclosure will become apparent upon reading the following detailed description when taken in conjunction with the accompanying drawings.

Drawings

FIG. 1 is a perspective view of a conveyor incorporating an exemplary safety control system for detecting a missing step constructed in accordance with the teachings of the present disclosure;

FIG. 2 is a schematic view of the steps in the return path near the landing;

FIG. 3 is a flow chart of an exemplary method for detecting a missing step in a conveyor;

4A-4B are schematic timing diagrams of pulse signals output by various sensors at a first conveyor speed and a second conveyor speed;

FIGS. 5A-5C are various views of a sensor positioned to detect a step roller shaft of an escalator step; and is

Fig. 6A-6C are various views of a sensor positioned to detect the path of movement of the posterior eye plate.

While the disclosure is susceptible to various modifications and alternative constructions, certain illustrative embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the disclosure to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the disclosure.

Detailed Description

Referring to the drawings and in particular to FIG. 1, an exemplary safety control system, or more specifically, a missing step detection device for a conveyor, is provided and indicated generally by the reference numeral 100. It should be understood that the teachings of the present disclosure can be used in constructing the above safety control systems and devices for detecting a missing conveyor step, and beyond the specific disclosure below. Those of ordinary skill in the art will readily appreciate that the following are only exemplary embodiments.

As shown in fig. 1, an exemplary conveyor 10 in the form of an escalator is provided having a first platform 12, a second platform 14, a plurality of moving pallets or steps 16 extending between the first and second platforms 12,14, and a moving handrail 18 disposed along the plurality of steps 16. Steps 16 of conveyor 10 are driven by a primary drive source (not shown), such as an electric motor or the like, and are caused to move between platforms 12, 14. The main drive source rotates the drive shaft and associated gears, thereby rotating a closed loop step belt or chain that mechanically interconnects the inner surfaces of the steps 16 from within the conveyor 10. Within each of the two landings 12,14, a sprocket 19 guides the step chain and the connected steps 16 through an arc to reverse the direction of step movement and form a return path in a cyclical manner. The handrail 18 is rotationally moved along the steps 16 by similar means at a speed comparable to the steps 16.

Still referring to fig. 1, the conveyor 10 may be equipped with a safety control device, such as the missing step detection device 100 shown. The missing step detector 100 may provide a plurality of sensors and control units 200 to observe various parameters of the conveyor 10. Specifically, the missing step detector 100 may observe the drive speed of the conveyor 10, the speed of the handrail 18, the presence of the steps 16 relative to the respective landings 12,14, and so on. To determine the conveyor or drive speed, the missing step detector 100 may provide a drive speed sensor 102. The drive speed sensor 102 may comprise one or more inductive sensors positioned proximate to the teeth of the sprocket 19, the sprocket 19 driving a step chain that interconnects the steps. Alternatively, the drive speed sensor 102 may comprise a photoelectric sensor or encoder positioned on the shaft of the sprocket 19, which is arranged to detect the rotational speed of the sprocket 19. To accurately detect the presence or absence of a step 16, the missing step detector 100 may include step roller sensors 104,106 in the landings 12,14 of the conveyor 10. Specifically, the step roller sensors 104,106 may include proximity sensors configured to detect metal in the step rollers or step roller shafts 20, as shown in FIG. 2. The missing step detector 100 may also include a handrail sensor 108 to observe the velocity of the handrail 18. The missing step detector 100 monitors the sensor readings, or signals related to the sensor readings, for any significant changes and fault indications. Once a change or malfunction has been detected, the missing step detector 100 can accordingly provide the necessary instructions to adjust the operation of the conveyor 10. For example, if the missing step detector 100 detects a critical fault, the missing step detector 100 may output the necessary command or control signals to the associated conveyor controller 110 to slow or stop the conveyor 10.

As shown in the flow chart of fig. 3, the missing step detector 100 correlates the output signals provided by the sensors to overcome the drawbacks associated with the prior art time-dependent step detection process. More specifically, the missing step detector 100 first determines an alternating drive pulse signal, which represents the conveyor drive speed and corresponds to the output of the drive speed sensor 102, in step S1. The missing step detector 100 may also determine a first step pulse signal in step S2 that represents the step 16 detected by the step roller sensor 104 of the first landing 12. Similarly, the missing step detector 100 may determine a second step pulse signal in step S3 that corresponds to the step 16 detected by the step roller sensor 106 of the second landing 14. From these pulse signals, the missing step detector 100 can determine a fixed value or characteristic that is unique to the conveyor 10 in question. As shown in step S4 in fig. 3, the missing step detector 100 may determine a ratio between the number of pulses in the drive pulse signal per step 16 or per step pitch. This ratio is a fixed value or characteristic associated with a particular conveyor 10 and does not change with conveyor speed or time. The missing step detector 100 may also determine a phase difference between the first and second step pulse signals corresponding to the two platforms 12,14, as shown in step S5. The phase difference is another fixed value associated with the conveyor 10 and does not vary with conveyor speed or time. In subsequent step S6, the missing step detector 100 may monitor any change in both the pulse ratio per step and the phase difference between the first and second step pulse signals. It is possible to correlate the pulse signals to produce a fixed value because there is a fixed relationship between the rotational speed of the main drive shaft and the time at which the next step roller or roller shaft 20 is detected. Therefore, the missing step detector 100 can effectively detect the missing steps at all the operation timings regardless of the conveyor speed, acceleration, deceleration, and the like. Furthermore, by relying on more than one relationship and creating redundancy, the missing step detector 100 is more likely to detect a true failure and less likely to trigger a false positive (false positive).

Turning to fig. 4A and 4B, an example timing diagram is provided to demonstrate a method by which a pulse-to-pitch ratio and a phase difference between step pulse signals can be determined. Signal a of fig. 4A shows a drive pulse signal of the conveyor 10 at the first speed. Signals B and C show step pulse signals representing steps detected at the first and second platforms 12,14, respectively. According to the method depicted in fig. 3, these pulse signals can be correlated to produce fixed values, i.e., pulse-to-space ratio and phase difference. For example, by counting the number of drive pulses in signal A that occur between successive step pulses in signals B or C, the pulse spacing ratio is determined to be 3: 1. Further, by comparing the phase shift between signals B and C, the phase difference can be determined to be 2 π/3 radians or 120.

Similar analysis of signals D, E, and F of fig. 4B results in substantially the same results, with fig. 4B showing the drive pulse signal and step pulse signal of the conveyor 10 at a second speed, which is half the drive speed of the example of fig. 4A, and the step pulse signal representing the steps detected at the first and second platforms 12,14, respectively. Specifically, as in the example of FIG. 4A, the number of drive pulses in signal D that occur between successive step pulses of signal E or F is determined to be 3:1, and the phase difference between signals E and F is 2 π/3 radians or 120. The pulse spacing ratio and the phase difference between the step pulse signals remain fixed for a particular conveyor 10 regardless of conveyor speed, acceleration, deceleration, etc. However, if the steps 16 are missing, misaligned, and/or undetected, they will change instantaneously to the pulse spacing ratio and the phase difference between the step pulse signals of the first and second platforms 12, 14. Thus, the missing step detector 100 can be configured to respond if and only if there is a large deviation in both the pulse-to-pulse ratio and the phase difference between the step pulse signals.

To ensure accurate detection of missing steps and to effectively apply the signal correlation methods disclosed herein, the step detection sensors 104,106 of the missing step detector 100 should be properly positioned. For example, the missing step detector 100 may require an inductive proximity sensor that exhibits a change in electrical characteristics in the presence of metal. The missing step detector 100 may also require the inductive sensor to output an alternating signal. However, an inductive sensor arranged to react to any and all metal passing in the steps will output a non-alternating continuous signal for the full pitch of the steps, and thus for the full length of the associated step chain. Thus, the sensors must be positioned and carefully positioned to react only to a small fraction of the steps being traversed to achieve non-continuous alternating outputs, as shown in FIGS. 5A-5C and 6A-6C. In the exemplary embodiment of fig. 5A-5C, the proximity sensor 104a of the escalator type conveyor 10a is sized to only aim at the step roller axle 20a passing over the steps 16a and is placed in extremely close proximity to the path of the step roller axle 20 a. In the exemplary embodiment of fig. 6A-6C, the proximity sensor 104b of the path of travel or conveyor 10b is sized to target only the trailing eye pallet 22b passing by the pallet or step 16b and is placed in extremely close proximity to the path of the trailing eye pallet 22 b.

Based on the foregoing, it can be seen that the present disclosure can provide a missing step detection system for a conveyor, such as an escalator, a moving sidewalk, and the like, that overcomes the deficiencies in the prior art. More specifically, the present disclosure provides methods for determining an alternating drive pulse signal representative of conveyor speed, determining pulse signals representative of steps detected at each landing, and correlating the signals for the purpose of detecting misaligned or missing steps. By correlating the sensor output signals of the conveyors, a fixed reference value or characteristic specific to the conveyor in question can be determined. These fixed values may include, for example, the ratio of drive pulses to step spacing and the phase difference between the step pulse signals, and are immaterial to conveyor speed and time. By utilizing more than one fixed value as a reference, the present disclosure provides redundancy and the detection function of a missing step at any speed or acceleration of the conveyor. Furthermore, by providing sensor outputs in the form of alternating pulse signals, a conveyor can be constructed that is fully compliant with current safety standards and regulations without the need for expensive certification sensors for measuring integrity.

While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure.

Claims (17)

1. An apparatus (100) for detecting a missing or misaligned step (16,16a,16b) of a conveyor (10,10a,10b) extending between a first platform (12) and a second platform (14), comprising:

at least one driving speed sensor (102) configured to detect a driving speed and output a driving pulse signal corresponding to the driving speed;

at least one first step sensor (104,104a,104b) and at least one second step sensor (106), the first step sensor (104,104a,104b) being arranged to detect each step (16,16a,16b) at the first landing (12) and to output a first step pulse signal corresponding to the step (16,16a,16b) at the first landing (12), the second step sensor (106) being arranged to detect each step (16,16a,16b) at the second landing (14) and to output a second step pulse signal corresponding to the step (16,16a,16b) at the second landing (14); and

a control unit (200) receiving the drive pulse signal and the first and second step pulse signals, the control unit (200) being arranged to determine a frequency of the drive pulse signal, determine a drive pulse ratio per step pitch, determine a phase difference between the first and second step pulse signals, monitor changes in the drive pulse ratio per step pitch and the step pulse signal phase difference, and provide instructions to adjust operation of the conveyor (10,10a,10b) in response to the detected changes.

2. The apparatus (100) of claim 1, wherein the control unit (200) provides instructions to adjust operation of the conveyor (10,10a,10b) only in response to detected changes in both the per step pitch drive pulse ratio and the step pulse signal phase difference.

3. The apparatus (100) of claim 1, wherein each of the first and second step sensors (104,104a,104b,106) is configured to detect only the step roller axis (20,20a) of the respective step (16,16a,16b) at the respective platform (12, 14).

4. The apparatus (100) of claim 1, wherein each of the first and second step sensors (104,104a,104b,106) is configured to detect only a rear eye pallet (22b) of a respective step (16,16a,16b) at a respective platform (12, 14).

5. The apparatus (100) of claim 1, wherein at least one of the step sensors (104,104a,104b,106) is configured to detect only the step roller axis (20,20a) of each step (16,16a,16b) at the respective platform (12,14), and at least one of the step sensors (104,104a,104b,106) is configured to detect only the back eye pallet (22b) of each step (16,16a,16b) at the respective platform (12, 14).

6. The apparatus (100) of claim 1, wherein each of the drive pulse ratio per step pitch and the step pulse signal phase difference remains substantially constant during acceleration and deceleration of the conveyor (10,10a,10 b).

7. The apparatus (100) of claim 1, wherein the drive speed sensor (102) is an encoder.

8. The apparatus (100) of claim 1, wherein the drive speed sensor (102) is a proximity sensor.

9. The apparatus (100) of claim 1, wherein each of the first and second step sensors (104,104a,104b,106) is a proximity sensor.

10. The apparatus (100) of claim 8, wherein each of the first and second step sensors (104,104a,104b,106) is an inductive sensor.

11. The apparatus (100) of claim 1, wherein the apparatus (100) further comprises a handrail speed sensor (108).

12. A method for detecting a missing or misaligned step (16,16a,16b) of a conveyor (10,10a,10b) extending between a first platform (12) and a second platform (14), comprising the steps of:

determining a drive pulse signal corresponding to the speed of the conveyor (10,10a,10 b);

determining a first step pulse signal corresponding to a step (16,16a,16b) at the first platform (12);

determining a second step pulse signal corresponding to a step (16,16a,16b) at the second platform (14);

determining a drive pulse ratio per step pitch;

determining a phase difference between the first step pulse signal and the second step pulse signal;

monitoring a change in each of the per step pitch drive pulse ratio and the step pulse signal phase difference; and is

Providing instructions to adjust operation of the conveyor (10,10a,10b) in response to the detected change.

13. The method of claim 12, wherein the step of providing instructions to adjust operation of the conveyor (10,10a,10b) occurs only in response to detected changes in both the per step pitch drive pulse ratio and the step pulse signal phase difference.

14. The method of claim 12, wherein each of the first step pulse signal and the second step pulse signal corresponds to a step roller axle (20,20a) of a respective step (16,16a,16b) at a respective platform (12, 14).

15. The method of claim 12, wherein each of the first and second step pulse signals corresponds to a rear eye pallet (22b) of a respective step (16,16a,16b) at a respective platform (12, 14).

16. The method of claim 12, wherein at least one of the step pulse signals corresponds to a step roller axis (20,20a) of each step (16,16a,16b) at the respective platform (12,14), and at least one of the step pulse signals corresponds to only a back eye pallet (22b) of each step (16,16a,16b) at the respective platform (12, 14).

17. The method of claim 12, wherein each of the drive pulse ratio per step pitch and the phase difference between the first and second step pulse signals remains substantially constant during acceleration and deceleration of the conveyor (10,10a,10 b).