The present invention relates to testing of the positional adjustment of a sensor, such as a missing step sensor in a people conveyor. Particularly, the present invention relates to a method for testing the relative positional adjustment of a sensor which is adapted for sensing a target element which moves relative to the sensor preferably within a predetermined distance thereof, a corresponding sensor arrangement as well as a people conveyor including such a sensor ar- rangement.

Missing step detection in people conveyors having an endless conveyor band comprised of a plurality of tread elements, like escalators and moving walks, is conventional. Sensors of different types, like tactile contact sensors and non- contact sensors like, optical, magnetic, inductive, capacitive sensors, are used for this purpose. One such sensor is disclosed in WO 2004/033355 A1 with the title "Safety Monitoring System For A People Conveyor" in the name of the pre¬ sent applicant, which is included in the present application by reference. In this particular document the people conveyor further includes a moving flange which moves together with the conveyor band when in use. The moving flange comprises a plurality of discs attached to the tread elements and a plurality of bridges each attached alternatingly between two consecutive discs. To each of the discs and bridges at least one marker is attached and the sensor is provided within a predetermined short distance of the moving path of such markers which are the target elements for the sensor. When a marker passes by a sen¬ sor, a sensor signal or sensor pulse is generated. The sensor is connected to an evaluation control. Once the evaluation control notices a lacking marker, the people conveyor is shut down and a "callback" signal is generated requiring the presence of maintenance personal for bringing the people conveyor back to service.

While this system is reliably shutting down the people conveyor in case of a missing step, bridge or disk, unnecessary shut-downs can occur, for example if a marker gets lost or in case of misalignment of a sensor with respect to the target elements. Unnecessary shutdowns and callbacks are cost expensive and annoying to the operators of people conveyors. Thus the industry is continu¬ ously searching for ways to eliminate such unnecessary shutdowns. WO 2004/033355 A1 suggest to provide at least two markers with each of the bridges and discs and to generate a shutdown signal only in case of detection of two subsequent missing signals. However, there still is the problem of un¬ necessary shutdowns due to misalignments of the sensor with respect to the target elements. Such misalignment can occur due to the sensor breaking loose or due to increasing clearances due to the normal wear in the system.

One way of reducing unnecessary shutdowns due to misalignment of the sen¬ sor with respect to the target elements is to physically inspect the alignment regularly, for example during maintenance, in order to become aware of a be¬ ginning misalignment at an early stage while the sensor is still generating sig¬ nals of sufficient quality. This approach is, however, difficult to perform in cases where the sensors are not easily accessible, for example where there are under the conveyor belt as with WO 2004/033355 A1. In this latter case the tread ele¬ ments need to be disassembled in order to allow for physical inspection of correct alignment.

Therefore it is the object of the present invention to provide a method which allows for testing the positional adjustment or positional alignment of the sen¬ sor with respect to the target elements without having access thereto.

In accordance with an embodiment of the present invention this object is achieved with a method for testing the positional adjustment of a sensor which is adapted for sensing a target element which moves relative to the sensor within a predetermined distance, having the following steps: - reading a value representative for a sensor signal; — comparing the sensor signal value with a sensor reference signal value; and — providing information on the sensor adjustment quality based on such comparison.

The method can be performed for example by a technician during maintenance of the people conveyor. The technician can for example use an electronic serv¬ ice tool which is connected to the maintenance interface of the people con¬ veyor. The respective sensor reference signal value(s) can be stored in the people conveyor or in the electronic service tool and the step of comparing and providing the information can either be performed within the people conveyor or in the service tool. It is also possible to automatically perform the test method within the people conveyor for example on a regular or continuous basis, i.e. for example once a day or once a week. The information of a begin¬ ning misalignment can be output by way of a warning signal at the installation site or can be transmitted by way of a remote elevator/escalator monitor to a remote monitoring center.

It is to be noted that this method can also be used for testing the positional ad¬ justment of the sensor at the time of assembly of the system, i.e. the people conveyor, etc. so that in addition to measuring and adjusting the necessary di— mensions between the sensor and the target elements correct adjustment or alignment can be confirmed by way of actually testing the adjustment on the basis of the sensor signal as produced. The method can also be used during any subsequent adjustment of the sensor subsequent to the original installation thereof, for example during maintenance, etc. Of particular advantage is, how— ever, the possibility to test the positional adjustment of the sensor with respect to the target elements in use without the need of disassembling parts of the re¬ spective system in which the sensor is used.

The sensor reference signal value can either be derived theoretically, for ex- ample, on the basis of the specific switch on/switch off behavior of the used sensor in combination with the passage time of the target element with respect to the sensor, i.e. the time required by the sensor elements to pass the sensor completely. Alternatively, the sensor reference signal value can also be an ac¬ tual measured value which is measured for example subsequent to the original 105 correct installation and positional adjustment of the sensor with respect to the target elements.

Preferably, the sensor signal value comprises at least one of the following val¬ ues: signal duration, signal intensity, and signal shape. The signal value can 110 also comprise a combination of specific signal values. In this context the signal refers to the individual pulse as generated by the sensor in the course of the passage of a target element. In the embodiment of a people conveyor having target elements attached to the tread elements, the bridges and/or the disks the subsequent passages of target elements along the sensor generate a signal 115 train comprising a plurality of individual signals or pulses. Lacking signals or pulses are an indication for a missing tread, disk or bridge. In the particular ap¬ plication of the present method with people conveyor the signal duration is preferred, as signal duration is a value which can easily be calculated on the basis of the passage time of the target element by the sensor, and the switch 120 on/switch off characteristics of the sensor. Therefore it is possible to calculate the sensor reference signal value in dependency of the speed of the target ele¬ ment. In people conveyors such speed value is frequently available, as it is needed for other purposes.

125 Therefore the sensor reference signal value preferably comprises at least one of the following values: signal duration, signal intensity, and signal shape. A combination of different values can also be used.

The present invention also relates in one embodiment to a method for testing 130 the positional adjustment of a sensor within a people conveyor, which is adapted for sensing a target element which moves relative to the sensor within a predetermined distance thereof and which comprises the steps as described above. 135 Preferably, the step of comparing the sensor signal value with the sensor refer¬ ence signal value includes the step of comparing the sensor signal value with at least two but preferably three sensor signal value ranges and of providing in the latter case of three ranges any of a "proper orientation"-information, and "ad¬ justment required"-information and a "no function"-information, respectively, 140 dependent on the sensor reference value range which corresponds to the ac¬ tual sensor signal value.

The present invention further relates in another embodiment to a sensor ar¬ rangement including a sensor which is adapted for sensing a target element us which moves relative to the sensor preferably within a predetermined distance, comprising an evaluation control having a memory for storing a sensor refer¬ ence signal value, and a comparator for comparing a value representative for a sensor signal with a sensor reference signal value and an output for providing information on the sensor adjustment quality base on such comparison. 150 The present invention preferably relates to a people conveyor including a sen¬ sor arrangement according to the present invention. Particularly, the people conveyor includes an endless conveyor band comprising a plurality of tread elements wherein tread elements comprise the target elements. 155 Preferably, the people conveyor further includes a moving flange moving in use together with the conveyor band, the moving flange comprising a plurality of disks attached to the tread elements and the plurality of bridges, each attached alternating between two consecutive disks" where in the disks and bridges 160 comprise the target elements.

Preferably, the evaluation control is part of the conveyor control.

The present invention can be used in people conveyors of the escalator and 165 moving walk type and also in elevators, for example for testing the adjustment quality of level sensors which are used for identifying the position with respect to the floor level, etc., as well as other types of sensors for application outside the people conveyor field. The invention and embodiments of the invention are described in greater detail 170 below with reference to the Figures, wherein

Fig. 1 shows part of a people conveyor for use with the present invention with parts thereof broken away for clarity;

175 Fig. 2 shows a detail of the people conveyor of Fig. 1;

Fig. 3 is a schematic representation of the positional arrangement of the sensor with respect to target elements; and

180 Fig. 4 is a plot of the sensor on/off characteristic with respect to the lateral dis¬ tance of the sensor to the target and showing the dependency of the signal length from the lateral distance.

Fig. 1 shows a people conveyor and particularly an escalator 2 including an 185 endless step belt 6 which is formed from a plurality of subsequent tread ele¬ ments 4. The tread elements 4 are connected to lateral drive chains 8. The drive chain 8 is formed of a plurality of chain links 10. The chain links 10 are con¬ nected with each other at joints 12. Instead of the chain links 10 with integrated teeth as shown in Fig. 1 conventional chain links can be used. The tread band 6 190 or conveyor band 6 is driven by a linear drive (not shown) or a conventional chain sprocket drive (not shown).

The passenger conveyor 2 comprises a moving flange 24 and an inner decking 26 which provides an upper cover for the moving flange 24. The moving flange 195 24 is formed of a plurality of disks 28 attached to the tread elements 4 and a plurality of bridges 30 which are positioned between each two consecutive disks 24. The disks 28 and bridges 30 are slidably attached with each other.

As can be seen in more detail in Fig. 2, attached to the disks 28 and bridges 30 00 are target elements or markers 34. The target elements 34 can be snap-on elements which are attached to ribs 32 which are provided on the disks 28 and bridges 30, respectively. In Fig. 2 a sensor 38 is shown. The sensor 38 is pref- erably of the contactless type, i.e. it can be an inductive sensor, a capacitive sensor, an optical sensor, etc. 205 The arrangement of sensor 38 and target elements 34 is schematically shown in Fig. 3. Arrow 40 represents the distance Sn between sensor 38 and target ele¬ ment 34. Arrow 36 represents the length St of the target element 34.

210 Scale 42 represents particular distance values S0, S+i, S-^ S+2, S-2. S0 represents the "factory adjustment", i.e. the optimum design distance between sensor 38 and target element 34. Arrow 44 represents the relative velocity V1 between sensor 38 and target elements 34, while arrow 46 represents the lateral move¬ ment of the target elements 34 with respect to the sensor 38. The cause for 215 such lateral movement can be intrinsic to the particular application, i.e. it can be the lateral movement of the step band to which the target elements 34 are at¬ tached with respect to the sensor 38 which typically attached to the truss (not shown) of the people conveyor 2. The lateral movement can vary due to wear in the particular system wherein the sensor arrangement which is generally 220 denoted with 48 is used. With an escalator, for example such lateral movement of the step band slightly increases due to wear.

Also due to wear or due to an impact on the sensor 38 or any target element 34 the distance Sn can change. Obviously, the distance can permanently change to 225 become smaller or larger as compared to the original distance. The distance can also dynamically change so that in the course of the movement of the tar¬ get elements 34 relative to the sensor, distance variation for example around S0 occur, which have an effect on the signal as procured by the sensor 38. Finally, this can result in bad sensor signals which can no longer be properly evaluated, 230 or processed. The sensor arrangement 48 of Fig. 3 further comprises an evaluation control 50 having a memory 52 for storing a sensor reference signal value and a comparator 54 for comparing a value representative for a sensor signal with the sensor reference signal value and an output 56 in the form of a display for providing information on the sensor adjustment quality based on the 235 comparison. The sensor reference signal value can either be calculated on the basis of predetermined data but can also be obtained by way of measuring ref- erence data for example immediately after "factory adjustment" has been per¬ formed.

With respect to the example of Fig. 3, the time required by the target element 34 for passing the sensor 38 completely is dependent on the velocity Vt of the target element 34:

The resulting pulse duration for pulse width tP of the dynamic sensor signal or pulse is also dependent of the specific switch on/switch off behavior of the sensor 38 as used. Frequently and particularly with an inductive sensor 38 this behavior depends on the distance Sn and function f(Sn) as shown in Fig. 4. Function f(S) is the sensor on/sensor off characteristic in dependency of the distance Sn between sensor 38 and target element 34. Consequently the pulse duration or signal duration has the following value:

tP = f(Sn) * SM

The representation of Fig. 4 details the correspondence between the signal du¬ ration tp and the lateral distance Sn between sensor 38 and target element 34. Similar relationships can also apply for signal intensity as well as signal shape on the one hand as well as other misadjustment or misalignments between the sensor 38 and the target element 34, for example hight or level differences be¬ tween sensor and target element 34 or angular misadjustments. On the basis of such variations of the sensor signal value, the respective misadjustment ranges can be determined which correspond to proper operation or which require ad¬ justment. It is also possible to define a further range where the sensor arrange- ment 48 is out of function or not functioning. In the present embodiment range I, which is defined between the distances S-i and S+i corresponds to proper operation. Range II, which is defined outside range I and between S_2 and S+2 corresponds to "adjustment required". Range III, which is outside range Il cor¬ responds to sensor arrangement 48 not functioning. Such range values, or in the particular embodiment distance values can be stored in memory 52 and /or can be used by the comparator 54. Particular range values are stored in mem¬ ory 52 and/or are compared with actual sensor values, the respective sensor reference signal values will typically be dependent on the speed of the target element 34. In this case it will be necessary to make sure that the target ele- 275 ments 34 move relative to the sensor 38 with the correct velocity, while a test of positional adjustment is conducted. This might not be necessary if the sensor reference signal values are calculated based on the velocity. The range values can then be calculated for example based on the particular percentage of signal duration, signal intensity, etc. at factory adjustment. 280 Instead of the display output 56 as shown in Fig. 3, any other output is possible. For example a simple warning light in case that an adjustment is required or a direct connection to the respective control for example of the people conveyor 2 in order to stop it when the sensor arrangement 48 is not functioning. The 285 evaluation control 50 does not necessarily have to be an integral part of the sensor arrangement 48. It is also possible to have a separate service tool in¬ corporating the evaluation control 50 or part of it. The technician can then con¬ nect the service tool with a service interface in order to perform the test. While with respect to the conveyor applications it normally is sufficient to test the po- 290 sitional adjustment of the sensor 38 with respect to the target element 34 only from time to time, for example in the course of maintenance of the people conveyor 2, it can also be advantageous to frequently perform such testing and use the respective test result in order to obtain information on the deviation overtime and to get market feedback on the alignment quality over years of for 295 example step band and sensor. A respective memory for data logging of the raw signal and/or evaluated signal in the evaluation control 50 or elsewhere can be provided.