Elevator drive speed sensor

Abstract

Disclosed is an elevator drive unit, the elevator drive unit including an elevator drive (1.3) and an elevator drive speed sensor (3), the elevator drive speed sensor (3) being configured for determining speed measurement values, the speed measurement values being indicative of a speed of a movable drive member of an elevator drive (1.3), the elevator drive (1.3) including a hoisting machine (2). The movable drive member is configured to move relative to a stationary drive member of the elevator drive (1.3) as the hoisting machine (2) is operated. The stationary drive member being in particular a stator (2.3), housing (2.2), or pedestal of the hoisting machine (2). The elevator drive speed sensor (3) includes an optical unit with an illumination device (3.1) and an image capturing device (3.2), a mounting structure (3.5) and a processing unit (3.3). Via the mounting structure (3.5), at least the optical unit is mounted, in particular rigidly mounted, with respect to the stationary drive member such that an image capturing region (ICR) of a measuring surface (MS) of the movable drive member can be illuminated by the illumination device (3.1) and the image capturing device (3.2) can capture the image capturing region (ICR), wherein the measuring surface (MS) has an arbitrary respectively non-encoded surface, in particular surface texture, wherein the image capturing region (ICR) is stationary with respect to the mounting structure (3.5). The processing unit (3.3) is configured to control the image capturing device (3.2) to sequentially capture images of the image capturing region (ICR) and to compute the speed measurement values using image correlation and / or optical flow analysis.

Description

[0001] ELEVATOR DRIVE SPEED SENSOR

[0002] The present invention is in the field of elevator technology. Specifically, it concerns elevators, elevator drive speed sensors, elevator drive units and methods for controlling the operation of elevators.

[0003] For speed measurement in elevators, rotatory encoders that are coupled to the rotor shaft of the elevator motor respectively hoisting machine are typically used. The most commonly used encoders are two-channel incremental encoders in the form of quadrature encoders, which provide two binary output signals which are phase-shifted by 90 degrees as the encoder shaft rotates, with the frequency being proportional to the rotatory speed. Other encoders that may be used are sine-cosine encoders, which provide two analogue sinusoidal output signals that are phase- shifted by 90 degrees.

[0004] Such encoders, however, are critical regarding their mounting at the hoisting machine, since they must be mounted concentrically with respect to the rotor shaft respectively the rotational axis of the hoisting machine with high precision, and any angular as well as radial offset with respect to the rotational axis of the hoisting machine needs to be avoided. In operation, they are susceptible to mechanical vibrations and shocks. Further, de-alignment can occur overtime in use.

[0005] Further, the room available for the encoder installation is typically restricted and the installation is subject to a variety of constraints. This aspect is particularly critical for the upgrading and modernization of existing elevators and their drives. Further, there is a large variety of drive controllers that need to be considered. As a consequence, a large variety of different encoders typically needs to be stocked by elevator manufacturing or modernization companies, which is inefficient. Form a technical point of view, only non-ideal solutions may be available.

[0006] Further, incremental encoders as typically used according to the state of the art are highly complex and comparatively expensive precision engineering devices that require careful handling.

[0007] A further systematic problem regarding the use of incremental encoders is the fact that due to their operational principle the output signals only change and accordingly provide information as encoder shaft rotates, with the angular resolution being constant. At standstill, the output signals are static. The data rate accordingly is zero at standstill and increases with increasing rotational speed. Elevator drives, however, need to operate in large speed range. Precise closed-loop control of the elevator drive is especially required at low speeds, e.g., for the precise levelling of the elevator car at a landing, while the torque that needs to be provided by the hoisting machine may be substantial. A typical drive controller of an elevator may operate with a control frequency of, e.g., 16kHz for the current control. A new speed measurement value is in principle required in each cycle, i.e., every 62.5 microseconds for correct operation of the current control loop in this example. However, in low-speed situations as mentioned, the data rate of incremental encoders is unfavorably low. Here, an encoder with extremely high angular resolution would in principle be desirable to provide sufficient information. At high speeds, on the other hand, the data rate as provided by an incremental encoder is generally high and may in fact cause issues regarding the real-time signal processing. If the encoder resolution is increased to improve the data rate at low speed, the issues regarding the signal processing at high speeds becomes worse. Further, the technical complexity and costs of an incremental encoder increase significantly with the resolution. In dependence of the overall design and of the elevator system, in particular the suspension of the cabin and the counterweight, the situation may be even worse.

[0008] To improve the situation regarding the insufficient data rate at low speeds, in particular at low speed, extrapolation schemes are known that generate virtual new data from past encoder signals. However, this approach is critical for various reasons, such as discontinuities that may occur when new real encoder data are received, which do not match the interpolation, resulting in apparent jumps. Further, a variety of plausibility and sanity checks as well as additional safety measures are required when relying on extrapolated data for the control.

[0009] WO2023222422A1 discloses the use of an optical tracking sensor at an elevator car for sensing a speed of an elevator car in an elevator shaft. The tracking sensor may provide two-dimensional images that are evaluated by way of digital image correlation and / or optical flow analysis. WO2024022868 discloses the use of an imaging sensor mounted at an outside of an elevator car. The imaging sensor may use digital image correlation and / or optical flow analysis. The imaging sensor is further configured for detecting one or more first markers in the elevator shaft. CN103213883B discloses an elevator speed measuring device capable of reducing environment affects during measuring the speed of an elevator. The elevator speed measuring device comprises a shooting portion and a computation portion, wherein the shooting portion shoots the dark field images of a supporting member which supports an elevator compartment and moves with the elevator compartment, and the computation portion calculates the speed of the elevator compartment according to the dark field images. EP2691328B1 discloses a feedback system for a motor of an elevator system. The feedback system may include a first sensor and a processing circuit. The first sensor may be disposed in proximity to a drive component of the elevator system and configured to detect a change in position of the drive component. The processing circuit may be configured to receive a first data signal from the first sensor corresponding to the change in position of the drive component and generate a feedback signal for controlling the motor based on the first data signal . CN 116519971a discloses a rotating shaft instantaneous rotating speed measuring device and method based on image relevancy. The rotating shaft instantaneous rotating speed measuring device comprises a rotating shaft system, an area-array camera, a data line and a computer. The method comprises the following steps: adjusting the pose of a camera to enable a target pattern to be located at the central position of an area array sensor; when the rotating shaft rotates, an end face image on the imaging sensor also rotates along with the rotating shaft, in the vibration process of the rotating shaft, the area-array camera performs continuous imaging on the end face of the rotating shaft, and then a series of obtained images are transmitted to a computer through a data line; and finally, processing the end face feature image sequence by adopting a feature image sequence processing module and a data processing module in the computer, and calculating instantaneous rotating speed information of the rotating shaft by applying a provided rotating speed measurement method.

[0010] It is an overall objective of the present disclosure to improve the situation regarding the drive speed measurement in elevator drives. One or more of the before-mentioned problems are solved fully or at least partly. In a general way, the overall objective is achieved by the subject of the independent claims. Exemplary and favorable embodiments are the subject of the dependent claims as well as the overall disclosure.

[0011] In an aspect, the present disclosure concerns an elevator drive unit. The elevator drive unit includes an elevator drive and an elevator drive speed sensor. The elevator drive speed sensor is configured for determining speed measurement values, the speed measurement values being indicative of a speed of a movable drive member of the elevator drive. The elevator drive includes a hoisting machine. The movable drive member is configured to move relative to a stationary drive member of the elevator drive as the hoisting machine is operated. The stationary drive member may in particular be a stator, housing, or pedestal of the hoisting machine. The elevator drive speed sensor includes an optical unit with an illumination device and an image capturing device, a mounting structure, and a processing unit.

[0012] Via the mounting structure, at least the optical unit is mounted, in particular rigidly mounted, with respect to the stationary drive member such that an image capturing region of a measuring surface of the movable drive member can be illuminated by the illumination device and the image capturing device can capture the image capturing region. The measuring surface has an arbitrary respectively non-encoded surface texture. The image capturing region faces the elevator drive speed sensor respectively its optical unit. The image capturing region is stationary, i.e., has a constant position and orientation with respect to the mounting structure and accordingly also the optical unit.

[0013] The processing unit is configured to control the image capturing device to sequentially capture images of the image capturing region and to compute the speed measurement values using image correlation and / or optical flow analysis. The elevator drive speed sensor is a solid-state device in the sense that it does not have moving elements.

[0014] In a further aspect, the present disclosure concerns an elevator. The elevator includes a hoistway, a car, optionally a counterweight and an elevator drive unit in accordance with the present disclosure. The car, and, if present, the optional counterweigh is arranged vertically movable in the hoistway. The car, and, if present, the optional counterweight is coupled to the hoisting machine via a flexible traction member for moving the traction member and thereby the car and optional counterweight by operating the hoisting machine. An elevator drive unit in accordance with the present disclosure can be an elevator drive unit for an elevator in accordance with the present disclosure.

[0015] In a further aspect, the present disclosure concerns a method for controlling operation of an elevator in accordance with the present disclosure according to any embodiment as discussed above and / or further below. The method includes controlling the hoisting machine at least in part based on the speed measurement values determined by elevator drive speed sensor. The elevator may include a drive controller that controls operation of the elevator drive. The drive controller may be operatively coupled to the elevator drive speed sensor to receive speed measurement values from the elevator drive speed sensor. The elevator may further include an elevator controller that is configured to control overall operation of the elevator and may in particular be configured to control operation of the drive controller. In some variants, a monitoring and / or supervision unit of the elevator is configured for executing the before-mentioned task in addition or additionally to the drive controller respectively in a shared manner.

[0016] The present disclosure further concerns an elevator drive speed sensor The elevator drive speed sensor is configured for determining speed measurement values, the speed measurement values being indicative of a speed of a movable drive member of an elevator drive. The elevator drive includes a hoisting machine. The movable drive member is configured to move relative to a stationary drive member of the elevator drive as the hoisting machine is operated. The stationary drive member may in particular be a stator, housing, or pedestal of the hoisting machine. The elevator drive speed sensor includes an optical unit with an illumination device and an image capturing device, a mounting structure, and a processing unit. The mounting structure is configured for mounting, in particular rigidly mounting, at least the optical unit with respect to the stationary drive member such that an image capturing region of a measuring surface of the movable drive member can be illuminated by the illumination device and the image capturing device can capture the image capturing region. The measuring surface has an arbitrary respectively non-encoded surface texture. The image capturing region faces the elevator drive speed sensor respectively its optical unit. The image capturing region is stationary, i.e., has a constant position and orientation with respect to the mounting structure and accordingly also the optical unit. The processing unit is configured to control the image capturing device to sequentially capture images of the image capturing region and to compute the speed measurement values using image correlation and / or optical flow analysis. The elevator drive speed sensor is a solid-state device in the sense that it does not have moving elements.

[0017] As will become more readily apparent in the following, an elevator drive speed sensor in accordance with the present disclosure can be used in a similar way as an incremental rotatory encoder that is conventionally used for elevator drives, but provides a number of advantages. In particular, an elevator drive speed sensor in accordance with the present disclosure offers a high arranging and mounting flexibility with respect to the elevator drive. Generally, the same type of elevator drive speed sensor may be mounted to a large variety of elevator drives, in particular hoisting machines, in dependence of their specific design and characteristics. Also, it may be equally used in newly manufactured elevator drives and for the modernization respectively upgrading of existing elevator drives. Due to the applied measurement principle, the complexity of and potential faults regarding the mechanical installation and alignment are substantially reduced, if not fully avoided. Also, generally inevitable measurement errors, caused, e.g., by mechanical vibrations, are averaged out.

[0018] An elevator drive speed sensor may be configured for various purposes. In particular, it may be configured to provide speed measurement values as input signal respectively feedback signal for a current control loop of a drive controller. In an embodiment, the drive controller is configured for controlling the hoisting machine by way of field-oriented control or vector control, respectively. Additionally, or alternatively, it may be configured to provide speed measurement values as input signal respectively feedback signal for a speed control unit. In an embodiment of a drive controller, the drive controller is a cascade controller with an inner current control loop and an outer speed control loop.

[0019] It is noted that the frequency respectively cycle time at which speed measurement values need to be provided may be different for different applications. In particular, for control a higher measurement frequency is generally required as for speed control in a cascade controller as mentioned, since the current control loop operates at a higher frequency than the speed control loop. As discussed further below in more detail, the elevator drive speed sensor may be configured to provide speed measurement values with different measurement frequencies respectively with different time steps between consecutive measurements simultaneously respectively in parallel. For this purpose, the elevator drive speed sensor may have a corresponding number of output channels.

[0020] The hoisting machine is a typically rotatory electrical machine, such as a PM (permanent magnet) synchronous machine, an asynchronous machine (ASM), a reluctance machine or a DC machine. While not essential, the elevator is throughout this document generally assumed to be a traction drive elevator. However, it may also be an elevator of different design, such as a positive drive elevator.

[0021] Via the mounting structure, at least the optical unit of the elevator drive speed sensor is in an operational configuration mounted to the stationary drive member. In an embodiment, only the optical unit is mounted to the stationary drive member, while other units or devices of the elevator drive speed sensor are arranged separately and spaced apart with respect to the optical unit. In a typical embodiment, however, the elevator drive speed sensor is designed as a compact and integral unit, typically with a sensor housing.

[0022] An arbitrary respectively non-encoded surface, in particular surface texture means that the surface texture has a structure, in particular micro structure, that is at least partially random, as typical for machined or otherwise fabricated workpiece surfaces. The surface texture is not known to the elevator drive speed sensor. Generally, the surface texture is not strictly periodic or otherwise coded. The surface texture - also known as surface finish or surface topology - is determined by small, local respectively microscopic deviations of the drive member surface from an ideally smooth surface, forming a generally random pattern of three-dimensional features such as ridges and valleys, respectively raised and depressed regions. It is noted that, while the surface texture is generally arbitrary, the presence of three-dimensional respectively structural features is required. The deviations from an ideal and smooth surface are typically smaller than 1 mm and may be in the range of 1 / 10 mm or below, such as few 1 / 100 mm or below 1 / 100 mm.

[0023] As discussed further below in more detail, the optical unit may be an image acquisition system. The illumination device includes a light source, in particular a LED (Light Emitting Diode) which emits light in the visible and / or invisible range, in particular IR (infrared) light, or may include a laser light source, such as an infrared laser diode. The illumination device may further include one or more optical components such optical beam forming and / or beam shaping elements and / or light guides, in dependence of the optical and mechanical overall design.

[0024] The image capturing device generally includes an image sensor and may further include additional optical components. In a typical design, the image capturing device includes at least one lens and an aperture that is optically arranged between the lens and the image sensor. The image sensor may generally be designed according to the state of the art, such as a CMOS image sensor. While not essential, the image sensor is typically a monochromatic image sensor. Typically, the image sensor is a two-dimensional image sensor with an, e.g., square image field with a pixel pattern of rows and columns. The number of pixels may, e.g., be between 10X10 and 100X100, such as 18X18 or 40X40. Other values may be used as well. In dependence of the overall design, the image sensor may in principle also be a one-dimensional sensor respectively line sensor with a single row of pixels. The image sensor may have an intensity resolution in a range of, e.g., 8 Bit to 16 Bit, such as 10 Bit or 12 Bit. The individual pixels are typically square, with an edge length in the range of some 1 / 10 th micrometers, for example in a range of 10 to 50 micrometers, such as 20, 30 or 40 micrometers. Image sensors having different characteristics or specifications may be used as well.

[0025] The design and the arrangement of the optical unit with respect to the movable drive member is favorably such that the surface texture of the image capturing region can be captured with high contrast. Typically, the light as emitted by the illumination device hits the image capturing region at a comparatively shallow angle, e.g. in a range of 5° to 30 , such as 10° to 20 . An optical axis of the image capturing device is favorably orthogonal or substantially orthogonal to the image capturing region. The image capturing device is favorably focused on the measuring surface respectively the image capturing region. The measuring surface generally reflects or bounces back at least part of the light from the illumination device to the image capturing device respectively the image sensor. In the images that are captured by the image sensor, raised features having a small distance to the optical unit, such as ridges, generally appear light, while recessed features having a large distance to the optical unit, such as valleys, generally appear dark.

[0026] The image capturing region is a comparatively small surface element of the measuring surface. While other designs may be used as well, it is typically square, with an edge length in a range of, e.g., 3 mm to 5 mm. For practical purposes, the image capturing region can be considered as substantially point-shaped and represented, e.g., by its center.

[0027] As the movable drive member moves relative to the stationary drive member and the thereto mounted elevator drive speed sensor, also the measuring surface moves relative to the elevator drive speed sensor respectively its optical unit. At every point in time, the image capturing region is the small surface portion of the measuring surface that is captured by the image capturing device. The image capturing region accordingly differs for consecutively captured image.

[0028] As discussed further below in more detail, the movable drive member is typically a substantially rigid object, e.g. a traction sheave or a rotor shaft of the hoisting machine. Alternatively, however, the movable drive member is as a whole not a rigid object, but deformable. This is the case, e.g., if a traction and / or suspension member, such as a rope or belt, serves as movable drive member. The expression measuring surface especially refers to a surface that can be captured by the image capturing device respectively image sensor as image capturing region as the movable drive member moves, with the image capturing region facing the optical unit of the elevator drive speed sensor at each point in time. The measuring surface can be and typically is part of a larger surface.

[0029] The processing unit includes the circuitry for controlling the image capturing device as well as signal processing of the captured images and is typically realized by one or more semiconductor components, in particular chips. The processing unit may in particular include a DSP (Digital Signal Processor), in particular an ISP (Image Signal Processor) with corresponding programming. In an embodiment, the processing unit as a whole or a part thereof is formed integrally with the image sensor as a single component respectively semiconductor chip. The image processing unit may also include one or more ASICs (Application-Specific Integrated Circuits).

[0030] Images are captured with an image capturing frequency or frame rate of typically several kHz, e.g., in a range of 10 kHz to 30 kHz, such as, e.g. 17 kHz, but may also have a higher image capturing frequency, such as 50 kHz, 100 kHz ,160 kHz or 200kHz. In an embodiment, the image processing unit is configured to vary the image capturing frequency in dependence of the measured speed of the movable drive member and may in particular be configured to increase the image capturing frequency with the speed of the movable drive member.

[0031] The elevator drive speed sensor may have an effective spatial resolution in a range of e.g., several hundred DPI (Dots per Inch), such 850 DPI or several thousand DPI, e.g., a range of 2000 DPI to 30000 DPI, such as 4000 DPI, 12500 DPI or 25000 DPI on the measuring surface. In an embodiment, the image processing unit is configured to compute interpolated images, the interpolated images having a higher spatial resolution than a physical spatial resolution of the image sensor. Corresponding interpolation algorithms are known in the art. Generally, the expression "image" may refer to a directly captured or an interpolated image.

[0032] A maximum path speed of the measuring surface that can be processed by the elevator drive speed sensor, also referred to as tracking speed, may, e.g., be in a range of 1 m / sec up to 10 m / sec, such as 2 m / sec to 5 m / sec. It is noted that the required tracking speed depends on the overall design and performance of the elevator as well as the positioning of the elevator drive speed sensor respectively its optical unit, as discussed further below in more detail.

[0033] Determining speed measurement values using image correlation and / or optical flow analysis may include executing a cross correlation algorithm, in particular a digital image correlation algorithm for pairs of consecutive images, in particular directly consecutive images. The image processing unit may be configured to compute a movement respectively displacement of the measuring surface between consecutive images. The images may be pre-processed, e.g., by noise reduction and / or interpolation as mentioned before. The displacement may be determined in an image sensor coordinate system of the image sensor as discussed further below. The processing unit is generally not configured to identify and track the movement of specific individual features. Instead, the processing unit is configured to determine the displacement of the measuring surface by minimizing a global difference between timewise consecutive images, in particular directly consecutive images. The displacement may be expressed by an image displacement vector as discussed further below. Corresponding image processing algorithms are known in the art from a variety of applications, such as optical mice as commonly used as input device respectively part of the user interface of, e.g., PCs, and may be used in the present context. Also, the optical unit may be designed in generally the same way as in an optical mouse.

[0034] In an embodiment, the three-dimensional surface texture of the measuring surface is determined, at least in part, by a surface roughness of the measuring surface. For machined metal, in particular steel, the mean roughness index or average surface finish is typically in the range of few micrometers, e.g., 5 micrometers or below, in dependence of the material and applied manufacturing processes. As appropriate, the measuring surface may be intentionally roughened to provide sufficient textural features.

[0035] In an embodiment, the movable drive member is configured to rotate with respect to the stationary drive member as the hoisting machine is operated, wherein movable drive member is in particular a rotor or rotor shaft of the hoisting machine, or a member rigidly coupled to the rotor or rotor shaft. Members that are rigidly coupled to the rotor shaft may, e.g., be a traction sheave or a brake disk of a machine brake of the elevator drive.

[0036] In an embodiment, the measuring surface is part of a front surface or a circumferential lateral surface of the movable drive member. A front surface of the movable drive member generally extends transvers to the rotational axis, while a circumferential lateral surface extends circumferentially around the rotational axis. It is noted that the measuring surface is generally part of a larger front surface respectively lateral circumferential surface of the movable drive member.

[0037] For such embodiment, the movable drive member is generally rotationally symmetrical with respect to a rotational axis. The rotational axis is fixed and may extend horizontally in an installed elevator. Other arrangements, e.g., with a vertical rotational axis, are possible. For a movable drive member that is configured to rotate, also referred to as rotating drive member, a direction that is aligned with respectively parallel to the rotational axis is referred to as axial direction. A direction perpendicular to the rotational axis and intersecting with the rotational axis is referred to as radial direction. A direction perpendicular to the axial direction and a radial direction is referred to as tangential direction.

[0038] For the measuring surface being part of a front surface of the movable drive member, the measuring surface is in particular an even surface having the shape of a concentric annular ring around the rotational axis. Due to the rotational moving direction, each point and accordingly each textural feature of the measuring surface moves on a circular path around the rotational axis. Correspondingly, the moving direction is for each point of the measuring surface tangential with respect to the rotational axis and accordingly different for each point in a stationary coordinate system, e.g., a cartesian coordinate system of the image sensor. The absolute value of the velocity vector, respectively the path speed, is for each point proportional to the distance from the rotational axis. Due to the generally small area of the image capturing region, approximation with an identical moving direction and path speed is possible. In dependence of the overall design of the elevator drive and especially the hoisting machine, using part of a front surface of the movable drive member as measuring surface may be favorable for the installation under given geometric and dimensional constraints. Further, since the path speed increases with the distance to the rotational axis, the elevator drive speed sensor respectively its optical unit can be mounted at an appropriate distance to the rotational axis in accordance with the the tracking speed of the elevator drive speed sensor. Further, this type of embodiment is in principle favorable regarding focusing since the measuring surface generally extends and rotates in a plane perpendicular to the rotational axis. By aligning the optical axis of the image capturing device perpendicular to the measuring surface respectively parallel to the rotational axis, it can be ensured that the image capturing region is parallel to a plane of the image sensor.

[0039] For the measuring surface being part of a circumferential lateral surface of the movable drive member, the path speed is given by the rotational speed of the movable drive member and the radius, specifically the distance of the measuring surface to the rotational axis. While different portions of a rotor or rotor shaft may have different diameters along the rotational axis, the flexibility for arranging the elevator drive speed sensor respectively its optical unit for optimal performance is limited. However, such arrangement may in dependence of the circumstances be preferrable under general design considerations and given constraints. It is noted that for such arrangement, the measuring surface and accordingly the image capturing region is not strictly even, but cylindrically curved. Due to the small size of the image capturing region, however, it can be approximated as even. The moving direction of each point on the measuring surface is tangential as mentioned before and perpendicular to the rotational axis. Relevant diameters in the context of an elevator drive may be, e.g. in a range of typically 80 mm or more, and may, e.g., for high rise elevators, also be more than 500 mm.

[0040] In alternative embodiments, the movable drive member may be a flexible traction member, such as a rope or belt, which couples the car and optionally a counterweight with the elevator drive.

[0041] In such designs, the measuring surface is given by a surface section of the flexible traction member.

[0042] In an embodiment, the speed of the movable drive member is a rotatory speed. This may in particular be the case for a movable drive member that is configured to rotate as discussed before. Here, the speed measurement values may, e.g., be in a unit of angle per time, such as 7s (degrees per second) or RPM (revolutions per minute). Alternatively, however, the speed of the movable drive member is a translational speed. Here, the speed measurement values may be in a unit of distance per time, such as m / s. As discussed further below, displacements can also be expressed in pixels and speeds in pixels per time for a given setup. Therefore, the speed measurement values may, e.g., also be a value in pixels for a given time step.

[0043] In an embodiment, the elevator drive speed sensor is arranged such that an optical path between the image capturing region and the optical unit extends through an air gap of the hoisting machine, in particular in a radial manner. Such arrangement can in particular be advantageous if the measuring surface is part of a circumferential lateral surface of the movable drive member, in particular the rotor. Here, the arrangement is particularly compact and potential problems due to dirt and the like are generally avoided.

[0044] In an embodiment, the capturing device includes a two-dimensional image sensor, the image sensor defining an image sensor coordinate system. The image sensor coordinate system may be a two-dimensional cartesian coordinate system based on the pixel arrangement of the image sensor. In an embodiment, the processing unit is configured to compute image displacement vectors, wherein an image displacement vector represents a displacement of the measuring surface over time in the image sensor coordinate system. Displacement vectors may be computed directly from captured images, or, if applicable, from interpolated images as mentioned before.

[0045] In an embodiment, the image displacement vectors are differential image displacement vectors. A differential image displacement vector is a displacement vector as determined by way of image correlation between timewise directly consecutive images. Alternatively, the displacement vectors are accumulated image displacement vectors. An accumulated image displacement vector can be computed by accumulating respectively summing up a number of consecutive differential image displacement vectors. The number of differential image displacement vectors to be summed up for each accumulated image displacement may be chosen as appropriate and may, e.g., be ten in a typical embodiment. A corresponding differential image velocity vector or accumulated image velocity vector may be computed in a straightforward manner form a differential image displacement vector or accumulated image displacement vector and the time step between consecutive images. Regarding the computation of speed measurement values from accumulated image displacement vectors as discussed below, the accumulation has the effect of an averaging.

[0046] For accumulation, the image capturing frequency needs to be a multiple of the measurement frequency at which speed measurement values are provide, in dependence of the number image displacement vectors that are accumulated.

[0047] It is noted that the unit of length in the images is generally pixels. A conversion into a physical unit of length, such as millimeters, however, is straight forward based on the design of the image sensor and the aspect ratio. Further it is noted that the computation of image velocity vectors is not absolutely required if the time step is known and favorably constant. In this case, the absolute value of the image displacement vectors, or a component thereof as discussed in the following can serve as speed measurement values.

[0048] In an embodiment, the processing unit is configured to compute the speed measurement values from a component of the displacement vectors along a nominal moving direction, wherein the moving direction is pre-determined. The nominal moving direction is a direction which corresponds to a moving direction of the measuring surface as captured by the image sensor. By way of example, assume the measuring surface to be part of a circumferential lateral surface element of a rotating movable drive member, e.g., the motor shaft, and assume the two-dimensional image sensor to be arranged such that the either of its axes, e.g., the x-axis, is parallel to the rotational axis. In this case, the nominal moving direction corresponds to the other axis, i.e., the y-axis, of the image sensor coordinate system. If, in another example, the optical unit is arranged such that the axes of the image sensor coordinate system are rotated by 45° with respect to the rotational axis, the nominal moving direction is at an angle of 45 in the Image sensor coordinate system. Similarly, e.g., for the movable drive member being a belt making a merely translational movement in the area that is captured by image sensor, the nominal moving direction would be aligned with one of the axes of the image sensor coordinate system if either of its axes is parallel to the translational moving direction of the belt.

[0049] Evaluating a component of the image displacement vectors along the nominal moving direction is favorable in that it allows distinguishing in the images the relevant movement from any superimposed noise respectively random movements that may be present, e.g., due to mechanical shocks or vibrations. The nominal moving direction may be stored in the processing unit.

[0050] In an embodiment, the elevator drive speed sensor is configured to execute a teach-in-routine. The processing unit is configured in the teach-in-routine to control the image capturing device to capture a sequence of teach-in images while the hoisting machine is operated and to compute the nominal moving direction from the teach-in images.

[0051] In the image displacement vectors, in particular accumulated image displacement vectors, a component corresponding to the nominal moving direction will far predominate over other components, in particular a component perpendicular to the nominal moving direction. Such component may be caused by distortions, e.g., mechanical vibrations and mechanical shocks, potentially present dust particles and the like. However, such distortions generally average themselves out over time for a correctly operating system. The nominal moving direction is accordingly easily recognizable as predominating direction from the computed image displacement vectors and / or image velocity vectors. Capturing the sequence of teach-in images and computing the nominal moving direction may be done, e.g., during commissioning of the elevator or commissioning of the elevator drive. The nominal moving direction may be stored in the processing unit. In another embodiment, the nominal moving direction is not computed from a sequence of teach-in images, but is determined based on the design, specifically the arrangement of the elevator drive speed sensor in relation to the movable drive member and pre-stored, e.g., in the processing unit.

[0052] In an embodiment, the processing unit is configured to compute a measurement uncertainty. Given a nominal moving direction and an image displacement vector, a transverse component of the image displacement vector transverse respectively perpendicular to the nominal moving direction may serve as measure for the measurement uncertainty. Also, the scalar product respectively an angle between the image displacement vector and the nominal moving direction may serve as measure for the measurement uncertainty. In the image sensor coordinate system, the absolute value of an aligned component of an image displacement vector, the aligned component being aligned with the nominal moving direction, reflects the required speed of the measuring surface respectively corresponds to a speed measurement value. The measurement uncertainty may be regarded as a circle having a radius corresponding to the absolute value of the transverse component, centered around the tip of the aligned component. It is noted that instead of image displacement vectors, image velocity vectors may be equally used since they are aligned with the image displacement vectors. Consequently, an image displacement vector or image velocity vector may be decomposed into an aligned component and a transverse component as mentioned, with the absolute value of the aligned component reflecting respectively corresponding to the speed measurement value and the transverse component reflecting the measurement uncertainty. Ideally, no transverse component is present.

[0053] The processing unit may be configured to compute the measurement uncertainty from a single displacement vector as explained or may be configured to compute the measurement uncertainty as averaged measurement uncertainty from a number of image displacement vectors and / or image velocity vectors. The processing unit may be configured to compute the measurement uncertainty repeatedly and / or continuously. In an embodiment, the processing unit is configured to compute and / or evaluate the measurement uncertainty only in phases of steady operation of the elevator drive, in particular in phases where the speed of the movable drive member is constant or substantially constant.

[0054] In an embodiment, the processing unit is configured to compute a measurement uncertainty from a series of consecutive image displacement vectors and / or image velocity vectors by way of statistic evaluation. The processing unit may in particular be configured to compute a measurement uncertainty from the absolute values of a series of consecutive image displacement vectors and / or image velocity vectors, and / or their component along the nominal movement direction as explained before. The standard deviation or a related measure may serve as uncertainty measure.

[0055] In an embodiment, the data processing unit is configured to determine from the captured images if the speed measurement values are erroneous. Determining if the speed measurement values are erroneous may be based on a determined measurement uncertainty and / or on based on a relation of the image displacement vectors and / or image velocity vectors in relation to the nominal moving direction.

[0056] As discussed before, the nominal moving direction should be predominating in the image displacement vectors and image velocity vectors. Speed measurement values may be considered erroneous if, e.g., the computed measurement uncertainty exceeds a measurement uncertainty threshold and / or a value of the transverse component exceeds a threshold value. Erroneous speed measurement values may occur, e.g., in case of a defect of the elevator drive speed sensor or if, e.g., the position of the elevator drive speed sensor respectively its optical unit relative to the movable drive member changes, e.g., due to the elevator drive speed sensor respectively its optical unit mechanically shaking and accordingly being misaligned. Potentially, erroneous measurement values may also be caused by dirt, dust and the like. The processing unit may be configured to provide a corresponding error signal in case of erroneous speed measurement values, e.g., to a drive controller. The drive controller may be configured to initiate further actions such as writing a corresponding error code to a log file and / or issuing a service request. The drive controller may further be configured to trigger an emergency stop of the elevator as applicable. In an embodiment, the processing unit is configured to provide an error signal if a single speed measurement value is erroneous. In an alternative embodiment, the processing unit is configured to assess the occurrence of erroneous speed as a function of time. An error signal may be generated, if e.g., a number of consecutive speed measurement values exceeds a threshold, a percentage of speed measurement values exceeds a threshold or an increasing trend of erroneous speed measurement values over time is detected.

[0057] In an embodiment, the elevator drive speed sensor is configured to provide speed measurement values for the elevator drive velocity at a pre-determined measurement frequency, the measurement frequency being independent form the drive velocity.

[0058] An elevator drive speed sensor in accordance with the present disclosure may generally be configured to provide speed measurement values at a desired constant or non-constant rate. In contrast, the output signals of an incremental encoder at standstill are static as explained before and change seldom respectively slowly at low rotational speed. For an elevator drive speed sensor in accordance with the present disclosure, in contrast, the measurement frequency only depends on the frequency with which images are captured, and the subsequent signal processing. The measurement frequency accordingly only depends on the design and performance of the elevator drive speed sensor. Therefore, an elevator drive speed sensor in accordance with the present disclosure is particular favorable at low speeds which occur, e.g. when levelling the car with respect to a landing. In accordance with the present disclosure, speed measurement values may be provided in a large frequency range from, e.g. 100 Hz to 20 kHz or more. An adaptive respectively non-constant measurement frequency, however, is also possible.

[0059] For a use of the speed measurement values as input respectively feedback signal for a current control loop as mentioned before, the measurement frequency may correspond to the operation frequency of the current control loop or be a multiple thereof. Similarly, for a use of the speed measurement values as input respectively feedback signal for a speed control loop, the measurement frequency may correspond to the operation frequency of the sped control loop or be a multiple thereof.

[0060] It is noted that the image capturing frequency may correspond to the highest measurement frequency or is favorably a multiple thereof to allow accumulation respectively averaging.

[0061] In an embodiment, the elevator drive speed sensor is configured additionally provide second speed measurement values at an in particular pre-determined second measurement frequency, the second measurement frequency being in particular lower than the measurement frequency as mentioned before. The measurement frequency and the second measurement frequency may in particular differ regarding a number of consecutive images that are accumulated. By way of example, the speed measurement values may be computed form accumulated image displacement vectors that are in each time computed from two differential image displacement vectors and the second speed measurement values may be computed from in each time ten differential image displacement vectors, resulting in the measurement frequency being five times the second measurement frequency. By way of example, the speed measurement values may be used for current control and the second speed measurement values may be used for speed control in a cascade control as mentioned before.

[0062] In an embodiment, the elevator drive speed sensor is configured to receive a trigger and / or synchronization signal and to provide speed measurement values in accordance the trigger and / or synchronization signal. The trigger respectively synchronization signal may be provided by the drive controller. Such embodiment is favorable for synchronizing the operation of the elevator drive speed sensor with the control loop or control loops of the drive controller.

[0063] In the following, exemplary embodiments are discussed on more detail with additional reference to the figures.

[0064] The figures show:

[0065] Fig. 1 an elevator in accordance with the present disclosure in a schematic view;

[0066] Fig. 2 a hoisting machine and the positioning of an elevator drive speed sensor;

[0067] Fig. 3 an exemplary elevator drive speed sensor in accordance with the present disclosure in a schematic structural view;

[0068] Fig. 3 an example for a measuring surface and image capturing region on a front surface of a movable drive member;

[0069] Fig. 4 an example for a measuring surface and image capturing region on a circumferential lateral surface a movable drive member;

[0070] Fig. 5 an exemplary elevator drive speed sensor in accordance with the present disclosure in a schematic structural view;

[0071] Fig. 6 an exemplary elevator drive speed sensor in accordance with the present disclosure in a schematic functional view;

[0072] Fig. 7 textural features of an image capturing region in a captured image;

[0073] Fig. 8 textural features of an image capturing region in a captured image captured a time step subsequent to Fig. 7;

[0074] Fig. 9 the determination of the aligned component of an accumulated image displacement vector, and the measurement uncertainty. In the following, reference is first made to Fig. 1, showing an elevator 1 in accordance with the present disclosure in a highly schematic view. The elevator 1 includes a car 1.1 and a counterweight 1.2 that are arranged vertically movable in a hoistway 1.5. The car 1.1 and the counterweight 1.2 are coupled via a flexible traction member 1.4, the traction member 1.4 including, e.g., one or more ropes or belts as generally known in the art. The traction member 1.4 can also serve as suspension member for suspending the car 1.1 and the counterweight 1.2 against gravity. The elevator 1 further includes an elevator drive 1.3 with hoisting machine 2 as discussed further below in more detail.

[0075] The elevator drive 1.3 includes a traction sheave 1.3.2 which is mounted to or formed integrally with a rotor shaft 2.1 of the hoisting machine 2. The traction member 1.4 is wound around and couples to the traction sheave 1.3.2 such that rotation of the traction sheave 1.3.2 via the hoisting machine 2 and / or gravity causes the car 1.1 and the counterweight 1.2 to move vertically in the hoistway 1.5 in opposite directions. The elevator drive 1.3 further includes one or more machine brakes 1.3.3 that are arranged to selectively break the rotor shaft 2.1 respectively the traction sheave 1.3.2.

[0076] Further, an elevator drive speed sensor 3 in accordance with the present disclosure and as discussed above and further below in more detail is foreseen. The elevator drive 1.3 and the elevator drive speed sensor may form an elevator drive unit. The elevator drive speed sensor 3 is in the shown design exemplarily arranged at a rear end of the hoisting machine 2, opposite the traction sheave 1.3.2. The elevator drive speed sensor 3 is configured to measure a rotational speed of the rotor shaft 2.1 of the hoisting machine 2, with R indicating the rotational axis. The elevator drive speed sensor 3 is rigidly mounted to a housing 2.2 of the hoisting machine 2. In the shown arrangement, the housing 2.2 is the stationary drive member and the rotor shaft 2.1 is the movable drive member.

[0077] The elevator drive speed sensor 3 is operationally coupled to a drive controller 1.6 of the elevator 1 via a communication link to provide speed measurement values and optionally further signals such as status and / or error signals to the drive controller 1.6. The drive controller 1.6 further controls operation of the elevator drive 1.3, specifically the hoisting machine 2 and the machine brake 1.3.2. At least control of the hoisting machine 2 is based at least partly on the speed measurement values as feedback signal. The drive controller 1.6 may be operatively coupled to an elevator controller (not shown) as mentioned in the general description before and may also be realized with an elevator controller in a partly or fully integral manner. The drive controller 1.6 may include the power electronics, such as an inverter, for powering the hoisting machine 2. Other setups are possible as well. The drive controller may in a design control the hoisting machine by way of field-oriented control respectively vector control. Further, the drive controller 1.6 may in an embodiment be a cascade controller, implementing in particular a current control loop and a speed control loop.

[0078] Apart from particular aspects as discussed before and in the following, the elevator 1 generally corresponds to a design as known and typical in the art. For the sake of clarity, Fig. 1 does further not show a number of components that are known in the art and typically present in an elevator, such as guide rails for the car 1.1 and the counterweight 1.2, an overspeed governor and safety brake, buffers and stops for the car 1.1 and the counterweight 1.2, optional compensation ropes and the like. Further, Fig. 1 does not show the at least two landings at different floors as well operation panels, such as a car operation panel (COP) and / or landing operation panels (LOPs), safety equipment and the like. Further, it is noted that the overall design of the elevator 1 may be different. By way of example, Fig. 1 shows a one-to-one suspension of the car 1. 1 and the counterweight 1.2, which, however, is not essential. Also, the elevator drive 1.3 may be arranged in a dedicated machine room over the hoistway 1.5 but may also be arranged in a headroom as well as in a pit within the hoistway 1.5.

[0079] In the following, reference is additionally made to Fig. 2, showing a hoisting machine 2 and associated elements in a highly schematic view. Generally, the hoisting machine 2 is designed as known in the art. It is noted that the windings and further components of the electromagnetic circuit of the hoisting machine are not shown in the interest of clarity. By way of example, the hoisting machine 2 may be a PM (permanent magnet) synchronous machine, but other designs may be used as well. The type of hoisting machine is not essential.

[0080] The rotor shaft 2.1 is fixed to and / or part of the rotor 2.4 in a concentric manner. Further, in a concentric manner, a stator 2.3 is arranged around the rotor 2.4 or a part thereof, with an air gap G between them. The rotor 2.4 with the rotor shaft 2. 1 is supported by bearings 2.5. Further in the shown design, two machine brakes 1.3.3 are foreseen that are exemplary realized as e.g., electromagnetically actuated disk brakes, with the brake disks (not separately referenced) being in each case rigidly mounted to or formed integrally with the rotor shaft 2.1. Further in the shown design, the traction sheave 1.3.2 is not a separate component but is formed by a section of the rotor shaft 2.1. At an axial end of the hoisting machine 2, a machine interface device 1.3.4 is exemplarily arranged and mounted to the housing 2.2 of the hoisting machine 2. The machine interface 1.3.4 may in particular include power connection terminals but also auxiliary terminals and circuitry as applicable.

[0081] Fig. 2 further shows various mounting options for mounting an elevator drive speed sensor 3 in accordance with the present disclosure at different positions Pl, P2, P3, P4. It is noted that, while in an embodiment a plurality of two or more elevator drive speed sensors 3 may in principle be present at different locations for the purpose of redundancy, only one elevator drive speed sensor 3 is typically present.

[0082] In the following, reference is additionally made to Fig. 3 and Fig. 4, illustrating the arrangement of the elevator drive speed sensor 3 at positions Pl or P2 in a highly schematic view. In position P 1, the elevator drive speed sensor 3 is arranged such that it faces a front surface 2. If of the rotor shaft 2.1 as shown in Fig. 3. The elevator drive speed sensor 3 is arranged at a radial distance from the rotational axis R. The measuring surface MS is in this design a circumferential ring-shaped part of the front surface 2. If. The image capturing region ICR is the small portion of the measuring surface MS that directly faces the elevator drive speed sensor 3 respectively its optical unit, respectively in the view of Fig. 3 is the portion of the measuring surface MS that is under the elevator drive speed sensor 3. As the rotor shaft 2.1 rotates, the image capturing region ICR moves along the measuring surface MS.

[0083] In Position P2, the elevator drive speed sensor 3 is arranged such that it faces a circumferential lateral surface 2. 1c of the rotor shaft 2.1, as shown in Fig. 4. The measuring surface MS is in this design a circumferential ring-shaped section of the circumferential lateral surface 2. If.

[0084] It is noted that in Fig 3 and Fig. 4, the measuring surface MS is optically emphasized for clarity reasons. In practice, however, it may be and typically is an indistinguishable part of a larger surface. However, the part forming the measuring surface surface MS or a larger part that includes the measuring surface MS may, e.g., be intentionally roughened or otherwise provided with three-dimensional textural features to ensure correct operation of the elevator drive speed sensor 3. In any case, the three-dimensional textural structure is not known to the elevator drive speed sensor 3. Position P3 is similar to position P2, but the elevator drive speed sensor 3 is arranged such that it faces a circumferential later surface 2.4c through the air gap G. In position P4, the elevator drive speed sensor 3 is arranged such that it faces an e.g., belt-type traction member 1.4 which may be a functional part of the elevator drive 1.3. For positions P2, P3, the elevator drive speed sensor 3 is favorably arranged such that the optical axis of its image capturing device is radial respectively intersects the rotational axis R. For position Pl, the optical axis of the image capturing device is favorably perpendicular to the front surface 2. If respectively parallel to the rotational axis R. For position P4, the optical axis is favorably perpendicular to an outer surface of the traction member 2.4. In any case, the elevator drive speed sensor 3 is stationary and does not move. By way of example, it may for positions Pl, P2 be integrated into the machine interface device 1.3.4. For positions P3, P4, the elevator drive speed sensor may, e.g., be mounted to the housing 2.2 of the hoisting machine 2, respectively to its stator 2.3.

[0085] In the following, reference is additionally made to Fig. 5, showing the structural design of an exemplary elevator drive speed sensor 3 in accordance with the present disclosure in a schematic structural view, together with image capturing region ICR. The elevator drive speed sensor 3 includes an illumination device 3.1 with a light source 3.1.1 in form of an LED. However, the light source 3.1.1 may also be a laser diode or other kind of suited light source. The illumination device 3.1 further incudes a light directing device 3.1.2. The light directing device 3.1.2 serves the purpose of forming the light emitted by the light source 3.1 1 and guiding it to illuminate the image capturing region ICR, as indicated by illumination light path ILP. While schematically represented by the illumination line path ILP as single path, it is to be understood that the light that exits the light directing device 3.1.2 is actually generally cone-shaped and generally illuminates at least the image capturing region ICR in a favorably substantially uniform manner. Favorably, the illuminated area is slightly wider than the image capturing region ICR.

[0086] The elevator drive speed sensor 3 further includes an image capturing device 3.2 that forms an optical unit together with the illumination device 3.1. The image capturing device 3.2 includes a two-dimensional image sensor 3.2.1, a lens 3.2.2 and an aperture 3.2.3. The image sensor 3.2.1 may, e.g., be a CMOS sensor with 40X40 pixels. In the shown design, the lens 3.2.2 is realized with the light directing device 3.1.2 in an integral manner from transparent material, such as PMMA (Polymethylmethacrylate) or the like. Other arrangements may be used as well. By way of the lens 3.2.2 and the aperture 3.2.3, the image capturing region ICR is imaged sharply by the image sensor 3.2.1, with OA as optical axis of the image sensor 3.2.1. If the image capturing region ICR is curved, as it is the case for a circumferential lateral surface as mentioned, the depth of field needs to be sufficient to cope with the curvature.

[0087] The elevator drive speed sensor 3 further includes a processing unit 3.3 with a DSP and / or other suited processing circuitry as discussed further below in more detail. The processing unit 3.3 may communicate with the drive controller drive controller 1.6 as mentioned before.

[0088] The components of the elevator drive speed sensor 3 as mentioned before are arranged on a PCB (Printed Circuit Board) 3.4 which serves both the purpose of electrical interconnection as well as mechanical basis and support. The elevator drive speed sensor 3 may further include a casing or housing 3.5 which may also serve as mounting structure. Other designs are possible as well.

[0089] In the following, reference is additionally made to Fig. 6, illustrating an exemplary elevator drive speed sensor 3 in accordance with the present disclosure in a highly schematic functional view, with a signal flow being indicated by dashed arrows.

[0090] The processing unit 3.3 of the elevator drive speed sensor 3 includes in the shown design an image sensor interface unit 3.3.1, an image interpolation unit 3.3.2, an image correlation unit 3.3.3, an accumulation unit 3.3.4, and a speed determination unit 3.3.5. Further, the processing unit 3.3 includes a sensor control unit 3.3.6 that controls overall operation of the elevator drive speed sensor 3, in particular the signal flow. The processing unit 3.3 may be realized by one or more components, in particular semiconductor components and may include a programmed DSP and / or one or more ASICs. While shown structurally separate, the image sensor 3.2.1 and / or the light source 3.1.1 may be formed integrally with some or all components of the processing unit 3.3. as common semiconductor component, as applicable. In the shown design, the sensor control unit 3.3.6 further receives a trigger respectively synchronization signal SYNC as discussed before from the driver controller 1.6. However, the drive speed sensor 3 may also operate in an unsynchronized manner with respect to the drive controller 1.6.

[0091] The image sensor interface unit 3.3.1 controls the capturing of images with the image sensor 3.2.1 and includes an electrical interface and control logic. As appropriate, the image sensor interface unit 3.3.1 may further implement low level image processing, such as noise reduction. The optional image interpolation unit 3.3.2 is configured to execute an image interpolation algorithm, thereby increasing the spatial resolution. By way of the image interpolation, every physical pixel of the image sensor 3.2.1 is divided into a larger number of virtual sub-pixels. Corresponding algorithms are known in the art.

[0092] The image correlation unit 3.3.3 is configured to execute a digital image correlation algorithm. Essentially, the image correlation unit 3.3.3 determines a two-dimensional displacement respectively a displacement in both directions of the image sensor coordinate system by which a subsequently captured image needs to be displaced relative to a previously captured, in particularly directly previously captured image such that a resulting difference is minimized. Corresponding algorithms can be based in particular on cross correlation and are known win the art. The determined displacement corresponds to a differential image displacement vector d.

[0093] The optional accumulation unit 3.3.4 is configured to accumulate respectively sum up a number of consecutive image displacement vectors d, respectively their components, thereby generating an accumulated image displacement vector D.

[0094] The speed determination unit 3.3.5 is configured to compute from an accumulated displacement vectors D corresponding speed measurement value .s\ Therefore, the speed determination unit 3.3.5 may be configured to compute from an accumulated image displacement vector D the absolute value Daof its aligned component Daalong the nominal moving direction mdnom,. as measure for the drive speed. The nominal moving direction mdnom may be stored in speed determination unit 3.3.5 explicitly or be implicitly given, e.g., by one of axes of the image sensor coordinate system. In an embodiment, Dais directly used as output respectively serves as speed measurement value .v. It is noted, however, that Daas described before generally is a value in pixels. Therefore, the speed determination unit 3.3.5 may further be configured to do a conversion into a physical distance unit, such as millimeters. Further, the speed determination unit 3.3.5 may be configured to do a transformation from displacement into speed, such as RPM or - in case of the movement being linear, m / s, based on the time step for capturing images, and provide the speed measurement values .s' in such physical unit. It is noted that the same evaluation may be done directly for differential displacement vectors if no accumulation unit 3.3.4 is foreseen. Further it is noted that the order of a number of steps may be altered. For example, it is of course also possible to do a conversion into speed prior to computing the component along the nominal moving direction mdnOm The speed determination unit 3.3.5 may further include interface circuitry for interfacing the drive controller 1.6 as mentioned before.

[0095] Further in the shown design, the accumulation unit 3.3.4 is configured to accumulate respectively sum up a second number of consecutive image displacement vectors d, respectively their components, thereby generating an accumulated second image displacement vector D2. For computing the accumulated second image displacement vector D2, a different and in particular smaller number of differential image displacement vectors d may be used. Further, the speed determination unit 3.3.5 is in the shown design configured to compute from an accumulated second image vector D2 a corresponding second speed measurement values .v. The speed measurement values .s' may for example used by the drive controller 1.6 for current control, while the second speed measurement values s-> may be used for speed control. It is noted that speed measurement values s and second speed measurement values s2 are computed and provided with different measurement frequency in accordance with the different number of consecutive differential image displacement vectors d that are accumulated.

[0096] Further, the speed determination unit 3.3.5 may be configured to compute a measurement uncertainty, in particular by decomposing an accumulated image displacement vector D into an aligned component Daaligned with respectively parallel to the nominal moving direction momand a thereto transverse component Dtand evaluating Dtas discussed in the general description above.

[0097] Further in an embodiment, the architecture of the elevator drive speed sensor 3 is somewhat different and the functionality of the speed determination unit 3.3.5 as explained before is implemented in the drive controller 1.6. In this case, the accumulated image displacement vectors D and / or, if applicable differential image displacement vectors d, are transmitted to the drive controller 1.6. This has the particular advantages that all information respectively values that depend on the actual setup, such as the nominal moving direction mdnOm or values required for the unit conversion need not to be stored in the processing unit 3.3, since the accumulated image displacement vectors D and differential image displacement vectors d are dependent on the design of the elevator drive speed sensor 3, but not the design of the elevator drive 1.3 and the positioning of the elevator drive speed sensor 3.

[0098] In the following, reference is additionally mad to Fig. 7, Fig. 8, Fig. 9, schematically illustrating aspects of the operation of an elevator drive speed sensor 3 in accordance with the present disclosure.

[0099] Fig. 7 and Fig. 8 illustrate images as captured by the image sensor 3.2.1 of the image capturing region ICR in two consecutive captured images with the moving direction of the movable drive member respectively the measuring surface MS being from left to right as indicated. In Fig. 7, the image capturing region ICR incudes textural features F. 1, F.2 F.3, F.4 of the measuring surface MS, which are accordingly present in the captured image. In the consecutive image of Fig. 8, textural feature F.2 is no longer present in the image capturing region ICR, while two new textural features F.5, F.6 are present. From the difference between the images, a differential image displacement vector is computed by way of image correlation as discussed before. It is noted, however, that the individual textual features are not tracked. Instead, the global difference between the images, resulting from the displacement of all textural features, is used by the image correlation algorithm for the displacement computation.

[0100] Fig. 9 illustrates the decomposition of an accumulated image displacement vector D and the assessment of the measurement uncertainty u. The coordinate system with x-axis and y-axis is the image sensor coordinate system. The nominal moving direction mdnOm of the measuring surface MS is exemplary assumed to be aligned with the x-axis. The accumulated image displacement vector D can decomposed into an aligned component Daand a thereto transverse component Dtas explained before. Ideally, only the aligned component Dawould be present and it's absolute value is indicative for the speed of the movable drive member respectively is used as basis for computing a speed measurement value .v. The transverse component Dtmay result from general noise, mechanical vibrations and / or misalignment. It is noted that the transverse component Dtand accordingly the measurement uncertainty u are significantly exaggerated in Fig. 9 for illustrative purposes.

Claims

1. - 27 -CLAIMS1. Elevator drive unit, the elevator drive unit including an elevator drive (1.3) and an elevator drive speed sensor (3), the elevator drive speed sensor (3) being configured for determining speed measurement values, the speed measurement values being indicative of a speed of a movable drive member of the elevator drive ( 1.3), the elevator drive (1.3) including a hoisting machine (2), the movable drive member being configured to move relative to a stationary drive member of the elevator drive (1.3) as the hoisting machine (2) is operated, the stationary drive member being in particular a stator (2.3), housing (2.2), or pedestal of the hoisting machine (2), the elevator drive speed sensor (3) including an optical unit with an illumination device (3.1) and an image capturing device (3.2), a mounting structure (3.5) and a processing unit (3.3); wherein via the mounting structure (3.5) at least the optical unit is mounted, in particular rigidly mounted, with respect to the stationary drive member such that an image capturing region (ICR) of a measuring surface (MS) of the movable drive member can be illuminated by the illumination device (3.1) and the image capturing device (3.2) can capture the image capturing region (ICR), wherein the measuring surface (MS) has an arbitrary respectively non-encoded surface, in particular surface texture, wherein the image capturing region (ICR) is stationary with respect to the mounting structure (3.5); wherein the processing unit (3.3) is configured to control the image capturing device (3.2) to sequentially capture images of the image capturing region (ICR) and to compute the speed measurement values using image correlation and / or optical flow analysis.

2. Elevator drive unit according to claim 1, wherein the surface texture of the measuring surface (MS) is determined, at least in part, by a surface roughness of the measuring surface (MS).

3. Elevator drive unit according to anyone of the preceding claims, wherein the movable drive member is configured to rotate with respect to the stationary drive member as the hoisting machine (2) is operated, wherein movable drive member is in particular a rotor (2.4) or rotor shaft(2. 1) of the hoisting machine (2), or a member rigidly coupled to the rotor (2.4) or rotor shaft(2.1).

4. Elevator drive unit according to claim 3, wherein the measuring surface (MS) is part of a front surface (2. If) or of a circumferential lateral surface (2.1c) of the movable drive member.

5. Elevator drive unit according to claim 3 or claim 4, wherein the elevator drive speed sensor (3) is arranged such that an optical path between the image capturing region (ICR) and the optical unit extends through an air gap (G) of the hoisting machine (2), in particular in a radial manner.

6. Elevator drive unit according to anyone of the preceding claims, wherein the speed of the movable drive member is a rotatory speed.

7. Elevator drive unit according to anyone of the preceding claims, wherein the image capturing device (3.2) includes a two-dimensional image sensor (3.2.1), the image sensor defining an image sensor coordinate system (x, y).

8. Elevator drive unit according to claim 7, wherein the processing unit (3.3) is configured to compute image displacement vectors, wherein an image displacement vector represents a displacement of the measuring surface (MS) over time in the image sensor coordinate system (x, y).

9. Elevator drive unit according to claim 7 or claim 8, wherein the processing unit (3.3) is configured to compute the speed measurement values from a component of the image displacement vectors along a nominal moving direction mdnOm, wherein the nominal moving direction is pre-determined.

10. Elevator drive unit according to claim 9, wherein the elevator drive speed sensor (3) is configured to execute a teach-in-routine, wherein the processing unit (3.3) is configured in the teach-in-routine to control the image capturing device (3.2) to capture a sequence of teach-in images while the hoisting machine is operated and to compute the nominal moving direction md nom from the teach-in images.

11. Elevator drive unit according to anyone of the preceding claims, wherein the processing unit (3.3) is configured to determine from the captured images if the speed measurement values are erroneous.

12. Elevator drive unit according to anyone of the preceding claims, wherein the elevator drivespeed sensor (3) is configured to provide speed measurement values at a pre-determined measurement frequency, the measurement frequency being independent form the speed of the movable drive member.

13. Elevator drive unit according to anyone of the preceding claims, wherein the image processing unit (3.3) is configured to compute interpolated images, the interpolated images having a higher spatial resolution than a physical spatial resolution of the image sensor (3.

2. 1).

14. Elevator (1), the elevator including a hoistway (1.5), a car (1.1) and an elevator drive unit according to anyone of the preceding claims, wherein the car (1. 1) is arranged vertically movable in the hoistway (1,5); wherein the car (1. 1) is coupled to the hoisting machine (2) via a flexible traction member (1.4) for moving the traction member (1.4) and thereby the car (1. 1) by operating the hoisting machine (2).

15. Method for controlling operation of an elevator (1) according to claim 14, the method including controlling the hoisting machine (2) at least in part based on the speed measurement values determined by the elevator drive speed sensor (3).

Images