ELEVATOR POSITION REFERENCE SYSTEMS AND MONITORING BUILDING SETTLEMENT USING AN ELEVATOR POSITION REFERENCE SYSTEM

Abstract

An elevator position reference system and a method of monitoring building settlement using such a system. The elevator position reference system includes a hoistway extending in a vertical direction. The system also includes a first position measurement tape extending vertically along a portion of the hoistway and an upper tensioning device, connected to an upper end of the first position measurement tape so as to apply a tensioning force in the upwards vertical direction. A lower end of the first position measurement tape is fixed within the hoistway. The system also includes a second position measurement tape extend vertically along at least some of said portion of the hoistway and a lower tensioning device, connected to a lower end of the second position measurement tape so as to apply a tensioning force in the downwards vertical direction.

Claims

1. An elevator position reference system (3), comprising: a hoistway (4) extending in a vertical direction; a first position measurement tape (8a) arranged in the hoistway (4) to extend along a portion of the hoistway (4) in the vertical direction; an upper tensioning device (10), connected to an upper end (20a) of the first position measurement tape (8a) so as to apply a tensioning force (30) to the first position measurement tape (8a) in the upwards vertical direction, wherein a lower end (22a) of the first position measurement tape (8a) is fixed within the hoistway (4); a second position measurement tape (8b) arranged in the hoistway (4) to extend along at least some of said portion of the hoistway (4) in the vertical direction; and a lower tensioning device (12), connected to a lower end (22b) of the second position measurement tape (8b) so as to apply a tensioning force (32) to the second position measurement tape (8b) in the downwards vertical direction, wherein an upper end (20b) of the second position measurement tape (8b) is fixed within the hoistway (4).

2. The elevator position reference system (3) of claim 1, wherein: the upper tensioning device (10) comprises a fixing portion (402) and a tensioning portion (404), wherein the fixing portion (402) is fixed to a first position within the hoistway (4) and the tensioning portion (404) is connected to the upper end (20a) of the first position measurement tape (8a) and is moveable relative to the fixing portion (402) so as to apply the tensioning force (30); and/or the lower tensioning device (12) comprises a fixing portion (402) and a tensioning portion (404), wherein the fixing portion (402) is fixed to a second position within the hoistway (4) and the tensioning portion (404) is connected to the lower end (22b) of the second position measurement tape (8b) and is moveable relative to the fixing portion (402) so as to apply the tensioning force (32).

3. The elevator position reference system (3) of claim 2, wherein the tensioning portion (404) comprises a resilient member (416).

4. The elevator position reference system (3) of claim 1, wherein the lower tensioning device (12) comprises a weight (502) connected to the lower end (22b) of the second position measurement tape (8b) and moveable in the downwards vertical direction relative to the hoistway (4) so as to apply the tensioning force (32).

5. The elevator position reference system (3) of claim 1, wherein the first position measurement tape (8a) and the second position measurement tape (8b) are arranged along the same wall of the hoistway (4).

6. The elevator position reference system (3) of claim 1, wherein for the majority of the at least some of said portion of the hoistway (4), along which both the first and second position measurement tapes (8a, 8b) extend, the first position measurement tape (8a) and the second position measurement tape (8b) are less than lm apart, optionally less than 50 cm, further optionally less than 10 cm, further optionally less than 5 cm.

7. An elevator system (1) comprising the elevator position reference system (3) of claim 1, and further comprising: an elevator component (2) moving along the hoistway (4) in the vertical direction; and at least one position measurement sensor (9a, 9b) mounted on the elevator component (2) and arranged to output a first position measurement reading from the first position measurement tape (8a) at a first position and a second position measurement reading from the second position measurement tape (8b) at the first position.

8. The elevator system (1) of claim 7, further comprising a computing device (25) arranged to calculate a difference between the first and second position measurement readings.

9. The elevator system (1) of claim 7, wherein the elevator component (2) is an elevator car (2), and further comprising a computing device (25) arranged to calculate an absolute elevator car position at the first position using the first and second position measurement readings.

10. A method for monitoring building settlement using an elevator position reference system (3) comprising a first position measurement tape (8a) arranged in a hoistway (4) to extend along a portion of the hoistway (4) in the vertical direction and a second position measurement tape (8b) arranged in the hoistway (4) to extend along at least some of said portion of the hoistway (4) in the vertical direction, the method comprising: taking a first position measurement reading from the first position measurement tape (8a) at a first position using a sensor (9a) moving with an elevator component (2) in the vertical direction; taking a second position measurement reading from the second position measurement tape (8b) at the first position using a sensor (9b) moving with the elevator component (2) in the vertical direction; and determining a difference between the first and second position measurement readings.

11. The method of claim 10, wherein the first position measurement reading and the second position measurement reading are taken at the same time.

12. The method of claim 10, wherein the elevator component is an elevator car (2), and further comprising: determining an absolute elevator car position at the first position using the first position measurement reading and the second position measurement reading.

13. The method of claim 10, further comprising, during an initial learning phase, taking at least one first calibration reading from the first position measurement tape (8a) at at least one calibration position using a sensor (9a) moving with the elevator component (2) within the hoistway (4); taking at least one second calibration reading from the second position measurement tape (8b) at at least one calibration position using a sensor (9b) moving with the elevator component (2) within the hoistway; and storing the first and second calibration readings in a memory.

14. The method of claim 10, further comprising transmitting at least one of: the first position measurement reading, the second position measurement reading, the difference between the first and second position measurement readings, and the absolute elevator car position, to a remote server (35).

15. The method of claim 10, wherein the elevator position reference system further comprises: an upper tensioning device (10), connected to an upper end (20a) of the first position measurement tape (8a) so as to apply a tensioning force (30) to the first position measurement tape (8a) in the upwards vertical direction, wherein a lower end (22a) of the first position measurement tape is fixed within the hoistway (4); and a lower tensioning device (12), connected to a lower end (22b) of the second position measurement tape (8b) so as to apply a tensioning force (32) to the second position measurement tape (8b) in the downwards vertical direction, wherein an upper end (20b) of the second position measurement tape (8b) is fixed within the hoistway (4).

Description

DRAWING DESCRIPTION

[0049] Some examples of this disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0050] FIG. 1 shows a perspective view of an elevator system including a position measurement tape, as is known in the art;

[0051] FIG. 2 shows a perspective view of an exemplary clip as shown in FIG. 1;

[0052] FIG. 3 shows a perspective view of an elevator system according to an example of the present disclosure;

[0053] FIG. 4 shows a first example of a tensioning device according to the present disclosure;

[0054] FIG. 5 shows a second example of a tensioning device according to the present disclosure; and

[0055] FIG. 6 shows a table representing first and second position measurement readings, and absolute position and difference data derived from those readings, taken on a series of occasions.

DETAILED DESCRIPTION

[0056] FIG. 1 shows a perspective view of an elevator system 100 as is known in the art. An elevator car 120 is arranged to move vertically within the hoistway 140, guided along guide rails 160 extending in the vertical direction. The hoistway 140 includes a position measurement tape 180. The position measurement tape 180 is fixed to a hoistway wall by an upper fixing device 110, connected to the upper end of the position measurement tape 180, and a lower fixing device 130, connected to the lower end of the position measurement tape 180. These fixing devices 110, 130 do not allow vertical movement of the respective ends of the position measurement tape 180. The elevator hoistway 140 also includes two guiding clips 150a, 150b. Each guiding clip 150a, 150b is located at a respective landing floor of the elevator system, close to a respective landing door arrangement 170a, 170b.

[0057] An exemplary guiding clip 150a as is known in the art is shown in greater detail in FIG. 2. The guiding clip 150a includes first and second fixing holes 152a, 152b, which allow the guiding clip 150a to be secured to a structure within the hoistway. In the example of FIG. 1 the guiding clips 150a, 150b are fixed to a wall of the hoistway 140, but it is also known to fix such guiding clips 150a, 150b to another structure such as one of the guide rails 160. The guiding clip 150a includes a first protrusion 154 and a second protrusion 156 arranged such that in use they contact opposite edges of the position measurement tape 180. Thus the first protrusion 154 prevents movement of the position measurement tape 180 to the left (as viewed from the perspective of FIG. 2) whilst the second protrusion 156 prevents movement of the position measurement tape 180 to the right (also as viewed from the perspective of FIG. 2) i.e. in the event of sideways movement of the position measurement tape 180, the tape will come into contact with the first protrusion 154 or the second protrusion 156 (depending on the direction of the movement) and the protrusions 154, 156 will resist further sideways movement of the position measurement tape 180.

[0058] The protrusions 154, 156 are bent so as to also pass in front of a front surface (the surface visible in FIG. 2) of the position measurement tape 180, and thereby also prevent movement of the position measurement tape 180 in the horizontal direction away from the guiding clip 150a, at least in the region of the first and second protrusion 154, 156. The first and second protrusions 154, 156 are not arranged to apply any pressure onto the front surface of the position measurement tape 180, but simply to come into contact with the position measurement tape 180 if it moves away from the guiding clip 150a so as to resist movement of the position measurement tape 180 away from the guiding clip 150a (and therefore away from the wall of the hoistway or other structure mounting the guiding clip 150a). Since the first and second protrusions 154, 156 do not apply pressure to the front surface of the position measurement tape 180, they do not restrict or hinder vertical movement of the position measurement tape 180 through the guiding clip 150a, as illustrated by the arrow 158. This means that the position measurement tape 180 is free to stretch, shift or sag in the vertical direction, e.g. as a result of temperature fluctuations in the hoistway.

[0059] The functioning of the elevator system 100 will now be explained with reference to FIGS. 1 and 2. The elevator car 120 moves vertically within the hoistway 140, along the guide rails 160, driven by any suitable drive system as is known in the art, and controlled by an elevator system controller (not shown). Although a roped elevator system 100 is illustrated, the system may instead be ropeless. A sensor 190 is mounted to the elevator car 120, in a position which is generally aligned in a horizontal direction with the position measurement tape 180. As the elevator car 120 moves along the hoistway 140 in the vertical direction, the sensor 190 moves up and down to different vertical positions along the position measurement tape 180. This can be used for absolute position monitoring of the elevator car 120.

[0060] The sensor 190 senses position markings e.g. increments, on the position measurement tape 180 e.g. using a camera. The sensor 190 can either process the collected data itself or pass the data to another component of the elevator system e.g. the elevator system controller, for further processing. This data is processed to determine a vertical position i.e. height, within the hoistway 140. For example, each position marking could be unique and could be looked up in a lookup table (created in an initial calibration process) which includes the corresponding height for each position marking. In this way the position measurement tape 180 is usable by the elevator system 100 to determine the vertical position of the elevator car 120 for any given position within the hoistway 140.

[0061] However, in many elevator systems 100 the height of the hoistway 140, and therefore of the position measurement tape 180, is substantial e.g. in high rise buildings. As with any material, the position measurement tape 180 can undergo thermal expansion as a result of temperature increases in the hoistway 140, and the resulting elongation can be significant (e.g. several mm) for the lengths of position measurement tape which are commonly used. For example, the material of a typical position measurement tape may have a thermal elongation factor of 1.6×10.sup.−5 K.sup.−1, which would give rise to a total length increase of 32 mm in an elevator system having a total hoistway height of 50 m, and experiencing a temperature rise of 40° C.

[0062] Since the upper and lower ends of the position measurement tape 180 of the prior art elevator system 100 are fixed to the wall of the hoistway 140, elongation of the position measurement tape 180 will create loose slack in the tape, able to freely pass through the guiding clips 150a, 150b. This therefore creates unpredictable changes and anomalies in the relative position of parts/markings of the position measurement tape 180, since the location of any excess length of the tape cannot be accurately predicted. This can therefore result in parts/markings of the position measurement tape moving away from their “standard” or “expected” position (e.g. during calibration), which can then negatively affect position measurements made using the position measurement tape 180.

[0063] An elevator system according to examples of the present disclosure, as described herein below with reference to FIGS. 3-6, seeks to address such shortcomings of the prior art elevator system 100.

[0064] FIG. 3 shows a perspective view of an elevator system 1 according to an example of the present disclosure. An elevator car 2 is arranged to move vertically within a hoistway 4, which extends in the vertical direction as shown. The elevator car 2 is guided along guide rails 6. The hoistway 4 includes a position reference system 3 which includes a first position measurement tape 8a and a second position measurement tape 8b, both shown extending along the same portion of the hoistway 4 in the vertical direction.

[0065] The first position measurement tape 8a has an upper end 20a which is connected to an upper tensioning device 10. The position measurement tape 8a also has a lower end 22a which is fixed within the hoistway 4. The upper tensioning device 10 applies an upwards tensioning force 30 to the first position measurement tape 8a in the upwards vertical direction.

[0066] The second position measurement tape 8b has a lower end 22b which is connected to a lower tensioning device 12. The second position measurement tape 8b also has an upper end 20b which is fixed within the hoistway 4. The lower tensioning device 12 applies a downwards tensioning force 32 to the second position measurement tape in the downwards vertical direction.

[0067] Some exemplary tensioning devices will be described in more detail with reference to FIGS. 4 and 5.

[0068] The elevator hoistway 4 may also include guiding clips (not shown) positioned along the length of each position measurement tape 8a, 8b (e.g. at regular intervals), which are the same as that described above with respect to FIG. 2 or similar enough to provide the same function. Such clips can be designed in any suitable way to allow for any vertical movement of the position measurement tapes 8a, 8b as a result of the tensioning forces 30, 32.

[0069] During operation of the elevator system 1, the elevator car 2 moves vertically within the hoistway 4, along the guide rails 6, driven by any suitable drive system as is known in the art, and controlled by an elevator system controller (not shown). Two sensors 9a, 9b are mounted to the elevator car 2. The first sensor 9a is in a position which is generally aligned in a horizontal direction with the first position measurement tape 8a. The second sensor 9b is in a position which is generally aligned in a horizontal direction with the second position measurement tape 8b. It will be understood that in other examples the position measurement tapes 8a, 8b may be located sufficiently close to each other that only a single sensor, or two sensors mounted next to one another, can sense the position measurement tapes 8a, 8b. For example, the two position measurement tapes 8a, 8b could instead be arranged on the same wall of the hoistway 4 rather than on opposite walls as shown. The sensors 9a, 9b may be mounted to the elevator car 2 using any suitable known arrangement.

[0070] Each sensor 9a, 9b senses position markings e.g. increments, on the respective first and second position measurement tapes 8a, 8b e.g. using a camera. The sensors 9a, 9b can either process the collected data themselves or pass the data to another component of the elevator system, e.g. a computing device 25 which may be part of the elevator system controller, for further processing.

[0071] This data is processed to determine a position, i.e. height, within the hoistway 4, and/or to determine building settlement information, as is described in greater detail below with reference to FIG. 6. Each position marking could be unique and could be looked up in a lookup table which includes the corresponding height for each position marking. In this way, each or both of the position measurement tapes 8a, 8b are usable by the elevator system 1 to determine the vertical position of the elevator car 2 for any given position within the hoistway 4. As described further below, a comparison of the position readings from the two position measurement tapes 8a, 8b can be used in addition, or alternatively, to determine information related to building settlement.

[0072] One, or each, of the sensors 9a, 9b may process position readings itself, or alternatively, the position readings may be transmitted to the computing device 25. The computing device 25 may be a part of any suitable component of the elevator system 1 e.g. an elevator controller, and may be located remotely from the rest of the elevator system 1. The connection of the computing device 25 to the sensors 9a, 9b may be physical i.e. wired, or wireless, and is represented only schematically by dashed lines in FIG. 3.

[0073] The computing device 25 may be arranged to calculate a difference between first and second position measurement readings, collected respectively by the first and second position sensors 9a, 9b from the first and second position measurement tapes 8a, 8b. The computing device 25 may be arranged to calculate an absolute elevator car position by taking an average of the first and second position measurement readings. The computing device 25 may then transmit the difference and/or the absolute elevator car position to a remote (e.g. cloud) server 35 as shown in FIG. 3.

[0074] In other examples, the computing device 25 (or the sensors 9a, 9b) may send the collected first and second position readings directly to the remote server 35. The remote server 35 may then calculate the difference and/or absolute elevator car position as described below.

[0075] The upper tensioning device 10 applies an upwards tensioning force 30, illustrated by upwards arrow. Since the lower end 22a of the first position measurement tape 8a is fixed in the hoistway 4, this upwards tensioning force 30 keeps the first position measurement tape 8a taut, so any elongation resulting from thermal expansion results in the position measurement tape 8a being pulled upwards by the tensioning device 10, but remaining taut along its length.

[0076] Similarly, the lower tensioning device 12 applies a downwards tensioning force 32, illustrated by downwards arrow. Since the upper end 20b of the second position measurement tape 8b is fixed in the hoistway 4, this upwards tensioning force 32 keeps the second position measurement tape 8b taut, so any elongation resulting from thermal expansion results in the position measurement tape 8b being pulled downwards by the tensioning device 12, but remaining taut along its length.

[0077] Therefore any thermal elongation (or contraction) of the tapes will result in an approximately equal magnitude of length change in each of the position measurement tapes 8a, 8b, but they will be “shifted” or extended slightly, in opposite directions, due to the opposite tensioning forces 30, 32 acting on the tapes 8a, 8b.

[0078] FIG. 4 shows a first exemplary tensioning device 400. This could be used as an upper tensioning device 10 or a lower tensioning device 12 as seen in FIG. 3. The tensioning device 400 has a fixing portion 402 and a tensioning portion 404. The fixing portion 402 in this example is in the form of a bracket which includes two holes 406a, 406b, through which fixing members (which in this example are bolts) can be passed to attach the fixing portion to a structure 408 within the hoistway 4, to fix the fixing portion 402 relative to the hoistway 4. The structure 408 may, for example, be a second bracket which is itself attached e.g. bolted, to a wall or to a guide rail. The fixing portion 402 also includes a tensioning plate 418, described further below.

[0079] The tensioning portion 404 is connected to an end of the position measurement tape 8a, 8b (which could be the upper end 20a of the first position measurement tape 8a or the lower end 22b of the second position measurement tape 8b) and is moveable relative to the fixing portion 402 so as to apply the tensioning force 30, 32 to the position measurement tape 8a, 8b. Specifically, the end of the position measurement tape 8a, 8b is looped around a first end of a tensioning bracket 410, and this tape end is then looped back to lie against the position measurement tape 8a, 8b. The end of the position measurement tape 8a, 8b is fixed in position relative to the rest of the position measurement tape 8a, 8b by a clamping mechanism 412, in which plates are arranged with the position measurement tape 8a, 8b and its end between the plates, and then fixed in opposing contact by the clamping mechanism 412. The other end of the tensioning bracket 410 is fixed on a rod 414. A resilient member 416, which in this example is a spring, is arranged on the rod 414, at the end which is further from the mounting bracket 414. The resilient member 416 is braced against the tensioning plate 418 of the fixing portion 402. The tensioning plate 418 includes a hole sized so that the rod 414 passes through the hole, but the resilient member 416 does not. Thus the rod 414 is able to slide through the hole, relative to the tensioning plate 418 which remains fixed relative to the hoistway 4 (since it is part of the fixing portion 402).

[0080] When the position measurement tape 8a, 8b is installed, the resilient member 416 is pre-compressed, so that the resilient member 416 is acting to try to expand, and therefore pushing against the tensioning plate 418 (which resists since it is fixed), causing a pull on the tensioning bracket 410, downwards (with respect to the view of FIG. 4) so as to apply tension to the position measurement tape 8a, 8b. If the position measurement tape 8a, 8b elongates due to thermal expansion then this will allow the resilient member 416 to expand slightly, moving the tension bracket 410 upwards (for tensioning device 10 of FIG. 3) or downwards (for tensioning device 12 of FIG. 3) and ensuring that the position measurement tape 8a, 8b is kept taut. Similarly, a reduction in length will apply a greater upwards or downwards force and re-compress the resilient member 416.

[0081] FIG. 5 shows a second exemplary tensioning device 500. This could be used as a lower tensioning device 12 for the position measurement tape 8b as seen in FIG. 3. The tensioning device 500 includes a weight 502. The weight includes a hook 504, to which a connection member 506 is attached. The lower end 22b of the position measurement tape 8b is also attached to the connection member 506. Gravity acts on the weight 502 to produce a downwards force which the position measurement tape 8b resists with its material strength i.e. resisting stretching of the position measurement tape 8b. The force produced by the weight 502 acts to tension the position measurement tape 8b, such that if the position measurement tape 8b elongates due to thermal expansion the end 22b of the position measurement tape 8b, and therefore the connection member 506 and the weight 502 to which it is connected will be able to move further downwards relative to the hoistway 4 under the force of gravity, therefore keeping the position measurement tape 8b under tension. The weight 502 provides a tensioning mechanism which does not need to be fixed in the hoistway 4 (and in fact works as a result of movement of the tensioning device 500 relative to the hoistway 4).

[0082] The functioning of the elevator position reference system of the elevator system 1 will now be described with reference to FIGS. 3 and 6.

[0083] During operation of the elevator system 1, the elevator car 2 moves vertically within the hoistway 4, along the guide rails 6. When the elevator car 2 stops or passes a particular position, which can be any vertical position i.e. height, in which both the first and second position measurement tapes 8a, 8b are present, the first sensor 9a and the second sensor 9b can take independent readings from the first position measurement tape 8a and the second position measurement tape 8b, respectively. These position readings can be carried out, as described above, for example by comparing a detected marking or other visible identifier, with a look-up table to give a position value.

[0084] An example of such position readings is shown in row 60 of FIG. 6. The column “Channel” indicates whether the reading is taken using the first sensor 9a detecting the first position measurement tape 8a (indicated as column “A”), or whether the reading is taken using the second sensor 9b detecting the second position measurement tape 8b (indicated as column “B”).

[0085] The readings in row 60 are taken on a first day, designated as day “D”. This may be a day on which system installation is completed and on which an initial learning phase is carried out. In the learning phase, the elevator car 2 is run up and/or down the hoistway 4 and position readings are taken at a number of positions of both the first and second position measurement tapes 8a, 8b, and recorded in a memory. Each position is recorded as corresponding to a particular calibrated, or absolute, position.

[0086] In this example, the first readings give a position of “100” (in arbitrary units) for the readings from both of the position measurement tapes 8a, 8b. The absolute elevator car position calculated from these readings is shown in column 66, and as represented in the column heading, is calculated by summing the readings derived from each tape, and dividing the total by two, i.e. an average of the two independent position readings. As discussed below, this can be a more accurate absolute position measurement than would be achieved using a single (possibly non-tensioned) position measurement tape.

[0087] The next column, 68, shows the averaged shift parameter. The averaged shift parameter is calculated by subtracting the second position measurement tape reading from the first position measurement tape reading, and dividing the total by two. This information represents the relative magnitude and direction of thermal elongation and/or building settlement. As shown in the table of FIG. 6, on day D both tapes read the same position value and their relative shift from the calibrated position is 0.

[0088] The position measurement is then repeated, at the same position, three days later, represented as “D+3” in row 62. As seen, on this day, the first sensor 9a takes a reading of “98” on the first position measurement tape 8a, rather than the previous reading of “100”. Assuming the position “values” are counted from the bottom of the hoistway 4, this means that the first position measurement tape 8a has shifted upwards, relative to day D, since the sensor 9a at the same position has read a lower value. Conversely, sensor 9b reads a value of “102” from the second position measurement tape 8b, showing this tape has shifted downwards.

[0089] As shown in column 66, the average of these two readings still gives the same absolute position value of “100” which is consistent with day D. Thus combining the values from these two oppositely tensioned tapes allows thermal elongation effects to be removed from an absolute position measurement, for improved accuracy.

[0090] On day D+3, the averaged shift parameter is −2, representing the direction of shift (i.e. first position measurement tape 8a shifted upwards, and second position measurement tape 8b shifted downwards), and also the relative magnitude.

[0091] The position measurement is then repeated again, at the same position, a further seven days later, so ten days after initial day D, represented as “D+10” in row 64. As seen, on this day, the first sensor 9a takes a reading of “104” on the first position measurement tape 8a, rather than the day D reading of “100”. Assuming the position “values” are counted from the bottom of the hoistway 4, this means that the first position measurement tape 8a has shifted downwards, relative to day D+3 and day D, since the sensor 9a at the same position has read a higher value. Conversely, sensor 9b reads a value of “96” from the second position measurement tape 8b, showing this tape has shifted upwards.

[0092] As shown in column 66, the average of these two readings still gives the same absolute position value of “100” which is consistent with day D and day D+3. Thus combining the values from these two oppositely tensioned tapes allows thermal elongation effects to be removed from an absolute position measurement, for improved accuracy.

[0093] On day D+10, the averaged shift parameter is 4 (as seen in column 68), representing the direction of shift (i.e. first position measurement tape 8a shifted downwards, and second position measurement tape 8b shifted upwards, which is the opposite of day D+3), and also the relative magnitude (twice as much shift as on day D+3). This shift parameter is indicative both of relative movements due to thermal elongation, and also of relative movements resulting from building settlement i.e. movement of the building.

[0094] As described above, some or all of the information represented in each of the rows 60, 62, 64 of FIG. 6 may be transmitted to a remote server 35 (which may be e.g. an Ethernet server). The information on the server 35 is then accessible, by a customer, building owner, building manager, maintenance person etc. for building and maintenance monitoring. This also allows long term building settlement to be monitored e.g. by sending the shift parameter values from column 68, and monitoring these over time.

[0095] While the examples discussed above relate to an elevator car 2 being used to take readings from a pair of position measurement tapes 8a, 8b arranged in the hoistway 4, it will be appreciated that the sensors 9a, 9b may be mounted to any elevator component moving along the hoistway 4 in the vertical direction, such as a counterweight or working platform. In at least some examples, the readings may be taken for the purpose of monitoring building settlement without being used to monitor the position of the elevator car 2.

[0096] It will be appreciated by those skilled in the art that the disclosure has been illustrated by describing one or more specific aspects thereof, but is not limited to these aspects; many variations and modifications are possible within the scope of the accompanying claims.