The present invention relates to a method and a controller for detecting a person in an elevator cabin. Furthermore, the invention relates to a method for saving energy in an elevator system and to an elevator system.

Persons in the elevator cabin may be detected in different ways. Usually, a load weight system is present that prevents an overloaded elevator cabin from moving. Since the load weight system is mainly targeted to detect an overloaded cabin, it may not give reliable values to detect a single person in the cabin. In particular, a child may be too light to trigger an overload detection.

Other solutions for person detection are cameras and infrared sensors. However, cameras may be too expensive, may be subject for vandalism and do not work in the dark.

Furthermore, a camera may have to be placed in a way that the complete cabin is monitored and an interior design may be influenced.

Infrared sensors are used in building automation to detect persons and to turn on lights. However, infrared sensors only can detect moving objects having a temperature different to the ambient, which may be a problem at high ambient temperature. Additionally, infrared sensors may have a limited angle of view and may be problematic to be integrated into an interior design of an elevator cabin.

WO 2011 029 479 Al mentions a weighting mat on the floor of an elevator car for weighting passengers.

US 2015 266 701 Al discloses a vibrating string sensor for load measurement.

EP 1 988 047 Al describes a load measurement device between two pulleys below an elevator cabin. There may be a need for a simple, economic and reliable method for detecting persons in an elevator cabin.

Such a need may be met with the subject-matter of the independent claims. Advantageous embodiments are defined in the dependent claims.

Ideas underlying embodiments of the present invention may be interpreted as being based, inter alia, on the following observations and recognitions. An aspect of the invention relates to a method for detecting a person in an elevator cabin.

An elevator cabin may be the part of an elevator system, in which persons are moved between stories of a building. The elevator system additionally may comprise a drive for moving the elevator cabin and automatic opening and closing doors to which the elevator cabin may be accessed. Furthermore, a control system of the elevator system is adapted for operating the drive, the doors, for receiving calls for the elevator cabin and/or for measuring the state of these components, such as, whether doors are opened or closed, where the elevator cabin is located, etc. The method may be performed by the control system. According to an embodiment of the invention, the method comprises: measuring a load signal with a load sensor, wherein a level of the load signal is indicative of a load inside the elevator cabin; analysing the load signal for ripples having more than a minimal deviation from an averaged load signal; and deciding that a person is in the elevator cabin, when ripples have been detected.

The load sensor may be a sensor that is adapted for generating a signal, i.e. the load signal, which is indicative of a load inside the elevator cabin. An analogue load signal usually may be an electric signal, wherein the level of the signal is encoded with a voltage value. The load signal also may be the digitized electric signal. For example, the load signal may be transported via a communication bus from the load sensor to a controller evaluating the load signal.

For example, the load signal may be proportional to a weight of the elevator cabin together with the load inside it. In such a way, the load inside the elevator cabin may be determined from the level of the load signal by determining the overall weight of the cabin and its load and by subtracting the known weight of the cabin from the result. However, with the present method, not an absolute value of the load in the cabin is used for detecting persons, but ripples in the load signals are analysed.

For example, while the elevator cabin is stopped or is moving with constant speed, the load signal may be expected to be a constant signal. Without a person inside the elevator cabin, there may be then no factor that may lead to a change of the load signal. Tests have demonstrated that a movement of a person in the cabin, even soft movements, leads to load signal changes. Such deviations of the signal may be used to conclude that there is a person present in the cabin.

In particular, the load signal is analysed for ripples to detect a person. A ripple in the load signal may be changes in the load signal which are faster and/or more often as the usually changes in the load signal caused by the movement of the elevator cabin and/or persons entering or leaving the elevator cabin. For example, the ripples may be defined as the difference of an averaged load signal (which may be averaged over a specific time interval) and the load signal itself.

To exclude ripples that are caused by other sources, such as vibrations of working motors, ventilators and/or moving vehicles near the elevator system, ripples, which are smaller than a minimal deviation, may be discarded for person detection. For example, the actual deviation from the averaged load signal may be defined by dividing the difference of the load signal from the load signal by the load signal. The ripples then may have a deviation that is higher as a specific value, which, however, may be very small.

Basing person detection on a load signal may have many advantages. The method may work independent from temperature. A load sensor may be provided which does not need to be visible in the interior of the elevator cabin. Thus, the sensor may not influence the interior design of the elevator cabin and may not be subject to vandalism. Furthermore, the method also may work in the dark, for example, when the elevator cabin light is switched off. Furthermore, the method may provide a further way to detect a person besides the overweight detection. The control system may get further information that may reduce the risk that passengers are entrapped in the elevator cabin. Thus, the danger of a defect alarm filter, a broken alarm button or any other reasons may be reduced.

A load sensor for overweight detection already may be present and/or the method may evaluate the load signal of an already present load sensor. No additional hardware and therefore no additional hardware costs may be necessary for this kind of person detection. The installation costs for additional hardware may be avoided.

There are many ways, how the load signal may be processed for the presence of ripples, which are indicative of a person moving inside the elevator cabin.

According to an embodiment of the invention, ripples are detected, when differences of values of the load signal at different time points are higher than a threshold difference. A controller may analyse the load signal for fast changes. For example, when a person is walking inside the elevator cabin, every step may cause fast accelerations that result in steep changes of the load signal. For example, the value of the load signal may be subtracted from a value of the load signal a time interval, such as between 1/10 and 1 second, before. When the difference of these values is higher than a threshold, it may be assumed that a person is present.

According to an embodiment of the invention, ripples are detected, when a gradient in the load signal is higher than a threshold gradient. It also may be that the load signal is numerically differentiated. The resulting differential load signal may be indicative of steep changes, which may be detected by comparing the difference load signal with a threshold.

According to an embodiment of the invention, ripples are detected, when a frequency spectrum of the load signal contains frequencies in a characteristic frequency range. It also may be that a frequency analysis is performed with the load signal. Such an analysis may be performed via discrete Fourier analysis. When frequency components of a specific frequency are present, such as between 3 Hz and 1/3 Hz, it may be assumed that a person is walking inside the elevator cabin. The load signal may be generated by any type of load sensor.

According to an embodiment of the invention, the load signal is based on a frequency of a vibrating component of the load sensor. For example, the load sensor may comprise a piezo element that changes its frequency, when compressed. The load sensor also may be a vibrating string sensor, which string changes its frequency, when deformed.

According to an embodiment of the invention, the load signal is based on a changing resistance of the load sensor. It also may be that the load sensor is based on hydraulic and/or pneumatic principles and/ or that it comprises a variable resistance or sliding resistance, which is used for producing the load signal.

According to an embodiment of the invention, the load signal is analysed for ripples, when the elevator cabin is stopped. It may be beneficial to detect persons inside the elevator cabin, when the elevator cabin is in stand-by and/or has a closed door. In this case, the ripples caused by a moving person may be clearly differentiated from other cause of vibrations.

According to an embodiment of the invention, the method further comprises: determining an absolute load in the cabin from the load signal. As already mentioned, the load signal from a load sensor that is also used for determining the load inside the cabin may be used for person detection as described herein. For determining the absolute load, the load signal may be transformed into a load value, for example, based on a lookup table or a formula.

According to an embodiment of the invention, the load signal is digitized and the digitized load signal is analysed for ripples. The digitized signal already may be generated by the load sensor, which is connected via a digital bus line with a controller, which performs the method as described herein.

A further aspect of the invention relates to a method for saving energy in an elevator system, which is based on the method for detecting a person as described in the above and in the following. According to an embodiment of the invention, the method comprises: determining, whether a person is in the elevator cabin with the person detection method described herein; and, when no person is detected in the elevator cabin, switching off electric loads in the elevator cabin. Such an electric load may comprise at least one of a ventilator and a light in the elevator cabin.

When a light weighted person is in the cabin such as a child, it may be that a load measurement system determines, that no person is in the cabin. The load measurement system may detect a minimal load but the resolution of the load measurement may be so that a light weighted person may not always be detected. In this case, the decision to switch the elevator cabin into a stand-by mode may be overwritten, when a person is detected inside the elevator cabin based on the method as described herein. Even, when the elevator is already in stand-by mode and the person starts to move. The switched off electric loads may be switched on, when the person is detected. For example, if the light in the elevator cabin is switched off, after the door is closed, the person will move, either to give a call or to try to open the door. In this case, the person may be detected with the method and the lights may be switched on again.

In particular, energy norms may request a low stand-by energy, which is measured as soon as the door has closed. Thus, the elevator cabin light and other electric loads should be switched off as soon as the door has closed, while ensuring that no one is in the cabin, to avoid panic situations. Such situations may be avoided using the method.

A further aspect of the invention relates to a controller for an elevator system adapted for performing the method as described in the above and in the following. For example, the controller may be situated near or in the drive of the elevator system and/or also may control the operation of the drive. The load signal may be received in the controller via a communication line from the load sensor to the controller. This communication line may run through the elevator shaft. The controller may comprise a microprocessor that performs the method as software program. A further aspect of the invention relates to an elevator system, which comprises an elevator cabin driven by a drive, a load sensor indicative of a load in the elevator cabin and a controller adapted for optionally controlling the drive and for performing the method as described in the above and in the following. Such an elevator system may have additional components, such as elevator doors, indicators and/or control panels provided outside of the doors, etc. Usually, the elevator system may be provided inside a multistory building.

According to an embodiment of the invention, the load sensor is provided outside of the elevator cabin. The method may be performed with the load signal of a sensor that is attached to an outside of the elevator cabin, to the rope for moving the elevator cabin and/or to a pulley for guiding the rope to the drive. In particular, the load sensor may be adapted for measuring the weight of the elevator cabin together with its load.

It shall be noted that possible features and advantages of embodiments of the invention are described herein partly with respect to the method, the controller and the elevator system. One skilled in the art will recognize that the features may be suitably transferred from one embodiment to another and features may be modified, adapted, combined and/or replaced, etc. in order to come to further embodiments of the invention.

In the following, advantageous embodiments of the invention will be described with reference to the enclosed drawings. However, neither the drawings nor the description shall be interpreted as limiting the invention.

Fig. 1 schematically shows an elevator system according to an embodiment of the invention.

Fig. 2 shows a diagram with a load signal used in a method according to an embodiment of the invention.

Fig. 3 shows a flow diagram for a method for detecting persons and saving energy according to an embodiment of the invention. The figures are only schematic and not to scale. Same reference signs refer to same or similar features.

Fig. 1 shows an elevator system 10 comprising an elevator cabin 12 movable in an elevator shaft 14 by a drive 16. The elevator system 10 furthermore comprises a central controller 18 (which may be a part of the drive 16 or at least arranged near the drive 16) for controlling the drive 16 and further equipment of the elevator system 10. For example, the central controller 18 may also control elevator doors 20 and further electric loads 22 inside the elevator cabin 12, such as a light and a ventilator.

The elevator system 10 comprises a load sensor 24, which is attached to an outside of the elevator cabin 12, for example as described in EP 1 988 047 Al . The load sensor 24 is adapted for generating a load signal 26, which is digitized and transmitted via a communication bus 28 to the controller 18.

Fig. 2 shows an example of a load signal 26, which is the frequency of a vibrating string sensor, which is bent with forces that are caused by an overall weight of the elevator cabin 12. Time is depicted in seconds to the right and the frequency is depicted in Hz to the top.

During the first 6 seconds, the load signal 26 has been recorded in a stand-by mode of the elevator cabin 12, in which the elevator cabin 12 is not moving. After that, a person inside the elevator cabin 12, which person has not moved during the first 6 seconds, starts to walk around. It can be seen that this movement causes ripples 30 in the load signal 26. Although, the frequency changes are very small compared to the value of the load signal 24, they may be detected. In the present example, the frequency is about 16 kHz, while the ripples or frequency changes are in the range of 5 Hz.

Fig. 2 shows that it is not necessary to know an absolute weight value to detect a person. The control 18 may just consider the changes of the load signal 24 to make such a detection.

It has to be noted that a similar load signal may be generated with a load sensor 24 that is based on other principles, for example, a hydraulic sensor with a variable resistance. Fig. 3 shows a flow diagram for a method for detecting a person in the elevator cabin 12, which may be performed by the controller 18.

In step S10, the load sensor 24 measures the load signal 26, digitizes it and sends it via the bus 28 to the controller 18.

The controller 28 then determines an absolute load in the elevator cabin 12 from the load signal 26. Based on a formula or a lookup table stored in the controller 18, the actual value of the load signal 26 may be transformed into a weight value. This weight value may be either the weight of the elevator cabinl2 and its load or may be the load directly.

With the weight value, the controller 18 can detect an overloaded elevator cabin 12 by comparing it with a weight threshold. When the weight value is higher than the weight threshold, the elevator cabin 12 may be prevented from moving.

In step SI 2, the controller 18 analyses the load signal 26 for ripples 30 having more than a minimal deviation from an averaged load signal 26. Step S12 only may be performed, when the elevator cabin is stopped 12 and the doors 20 are closed, i.e. in a stand-by situation.

Characteristic ripples 30 for a person moving in the elevator cabin 12 may be detected in different ways. For example, as shown in Fig. 2, the controller 18 may determine a difference between a minimal and a maximal value of the load signal 26 within a specific time interval, such as 2 seconds. For example in Fig. 2, in the first 6 seconds, this difference is about 5 Hz, while after that this difference raises to 15 Hz. Thus, a difference of more than 10 Hz may indicate a person moving in the elevator cabin. In general, the controller 18 may detect characteristic ripples 30, when differences of values of the load signal 26 at different time points are higher than a threshold difference.

Another possibility is that the load signal 26 is numerically differentiated. In particularly, the load signal 26 may be firstly averaged with a sliding time window in a range from 0.1 to 0.5 seconds for suppressing noise. Secondly, a gradient signal may be calculated. It can be seen that the gradient of the load signal may raise up above 10 Hz per second in the second part of Fig. 2, where a person is moving. In the first part, below 6 seconds, the gradient is substantially 0. In general, the control 18 may detect characteristic ripples 30, when a gradient in the load signal 26 is higher than a threshold gradient.

A further possibility is to determine a frequency spectrum of the load signal 26 in a sliding window, for example for the last 10 seconds from the actual time point. As can be seen from Fig. 2, frequency components between 1 Hz and 3 Hz arise in the load signal in the second part, where a person is moving. The control 18 may detect characteristic ripples 30, when a frequency spectrum of the load signal 24 contains frequencies in a characteristic frequency range.

It has to be noted that these possibilities for detecting ripples 30 may be combined.

In step SI 4, the controller decides that a person is in the elevator cabin 12, when ripples 30 have been detected, which characteristics for a person are moving inside the elevator cabin 12.

In step SI 6, the information about a person being present in the elevator cabin 12 may be used for support an energy saving functionality of the elevator system 10.

For example, when the elevator cabin 12 is in a stand-by mode and when no person is detected in the elevator cabin 12, for a specific time, such as 5 seconds, the controller 18 may switch off electric loads 22 in the elevator cabin 12.

It also may be that the electric loads 22 are switched off, when the elevator cabin 12 enters a stand-by mode and that the person detection method is used to ensure that no person is present in the elevator cabin 12. This stand-by mode may be initiated based on other information as the person detection.

For example, when a trip of the elevator cabin 12 is finished, the door 20 is closed, no call for the elevator cabin 12 is present and the absolute load weight, which may be determined from the load signal 26 as indicated above, is below a threshold (such as 50 kg) a timer for a first time interval may be started. If the timer expires, then the electric loads 22 may be switched off. When after the starting of the timer, a person is detected based on ripple analysis, the electric loads 22 may be switched on again and the timer may be restarted for a second time interval. After the timer expires, the electric loads may be switched off again.

The first time interval and the second time interval may be different. For example, the first time interval may be 0 s, i.e. the electric loads 22 may be switched off immediately after entering the stand-by mode. If then a person is detected, the electric loads 22 may be switched on for a couple of seconds.

The person detection method may not only be used for saving energy but also for supporting other functions of the elevator system 10. For example, some controller functions may require an empty elevator cabin, such as visitor control to send an empty car to a visitor and/or an emergency service in a hospital.

The person detection method also may be used for supporting an alarm system of the elevator cabin 12. Such an alarm system may comprise an alarm button in the elevator cabin 12, which may be pressed by a person in the elevator cabin 12, for generating an alarm, for example, when the elevator cabin stops moving between two floors and the person is entrapped.

The person detection method may be used to detect persons entrapped in the cabin 12, even when an alarm button is broken. There also may be the case that a person is entrapped and does not press the alarm button for various reasons (as being too shy, mentality or physically not capable or on purpose as crime). If a person is detected in an elevator cabin for a long time (such as longer than 10 minutes), then an alarm may be generated automatically. In this context, one approach may be to not have an alarm button at all and to send out alarms automatically when entrapped persons are detected.

Finally, it should be noted that the term "comprising" does not exclude other elements or steps and the "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims. List of reference signs

10 elevator system

12 elevator cabin

14 elevator shaft

16 drive

18 central controller

20 elevator door

22 electric load

24 load sensor

26 load signal

28 communication bus

30 ripples