Patent Publication Number: US-2023159080-A1

Title: Tdr-based system for detection of hand touch positionings on an object, particularly on a steering wheel for the purpose of hand gesture recognition

Description:
TECHNICAL FIELD 
     The invention relates to a method of recognizing a hand gesture established by a sequence of hand touch positionings on an object, particularly on a steering wheel, a sensing system for detection of hand gestures on an object, particularly on a steering wheel, by carrying out such method, a steering wheel with hand gesture recognition comprising such sensing system, and a software module for automatically carrying out such method. 
     BACKGROUND 
     In the field of automotive vehicle sensor application, it is known to employ sensors for so-called Hands off Detection (HOD) systems, in which one or more sensors provide information about whether a driver has his hands on a steering wheel of a vehicle or not. This information can be provided as input to an Automatic Driver Assistance System (ADAS) such as an Adaptive Cruise Control (ACC), which, based on the provided sensor signal, can alert the driver and remind him or her to take control of the steering wheel again. In particular, such HOD systems can be used in support to fulfill a requirement of the Vienna convention that the driver must remain in control of the vehicle at all times. HOD systems may as well be employed in a parking assistance system or an ADAS that is configured for evaluating a driver activity at high speed. 
     It is further known to employ capacitive sensors in vehicle HOD systems. 
     By way of example, WO 2016/096815 A1 proposes a planar flexible carrier for use in steering wheel heating and/or sensing of the presence of the driver&#39;s hand(s) on the steering wheel. The planar carrier, which can be employed for mounting on a rim of a steering wheel without wrinkles, comprises a portion of planar flexible foil of roughly rectangular shape having two longitudinal sides and two lateral sides. A length B of the lateral sides is 0.96 to 1.00 times the perimeter of the rim. A number of N cut-outs per unit length are provided on each of the longitudinal sides, wherein the cut-outs of one side are located in a staggered fashion relative to opposing cut-out portions on the opposite side. The determining of an optimum shape and size of the cut-outs is described. Further described is a heat carrier, a heating and/or sensing device and methods for their production. 
     Multi-zone HOD capacitive sensor systems are known in the art that comprise a plurality of distinct and independent sensing zones along the steering wheel. These HOD capacitive sensor systems are capable of distinguishing various ways of holding the vehicle steering wheel by the driver (one hand, two hands, angular position). 
     For instance, European patent EP 1 292 485 B1 describes a steering wheel for a vehicle, which comprises a steering ring, a hub, and at least one spoke connecting the steering ring and the hub. On the steering ring, sensors are arranged in a distributed manner along the circumference of the steering ring, extending over the entire length of the steering ring. The sensors may be configured for operating on a resistive, capacitive or inductive basis. The sensors are subdivided into a plurality of segments arranged one behind another in the longitudinal direction of the steering ring. The spacing between two segments of a sensor from one another in the longitudinal direction of the steering ring is smaller than a finger width, wherein the segments of the sensors, in the longitudinal direction of the steering ring, are shorter than a finger width. By that, the thumb and the fingers of the hand can be reliably distinguished from each other and a high spatial resolution is achieved. 
     With such capacitive HOD systems it is only possible to detect a touch positioning or a grasping hand positioning based on dedicated sensor zones. A position detection is only possible based on the sensor area size. 
     Employment of other sensors has also been proposed for HOD applications. WO 2019/086388 A1 describes a system for detecting whether at least one hand of a user is on a steering wheel. The system is in general based on a time-domain reflectometry (TDR) measurement. The system comprises a signal line that extends from a first point to a second point and is disposed along at least a portion of a surface of the steering wheel. The system further includes a detection unit that is coupled to the first point. The detection unit is configured to send a time-dependent detection signal traveling along the signal line, to receive a reflected signal traveling along the signal line and to detect the presence of a hand on the surface based on the reflected signal. 
     SUMMARY 
     It is an object of the invention to provide a sensing system of low complexity that can be employed for at least detecting hand touch positionings on an object, particularly on a steering wheel, in particular a vehicle steering wheel, for the purpose of recognition of hand gestures that are established by a sequence of hand touch positionings on an object, particularly on the steering wheel. 
     This object is achieved by a method of recognizing a hand gesture established by a sequence of hand touch positionings on an object, particularly on a steering wheel, a sensing system for detection of such hand gestures, and a steering wheel with hand gesture recognition according to the claims. 
     In one aspect of the present invention, the object is achieved by a method of recognizing a hand gesture established by a sequence of hand touch positionings on an object, particularly on a steering wheel, by operating a sensing system. The sensing system comprises at least one electrically conducting signal line, which is arranged to extend along a part of a surface of the object with a priori knowledge about a relation between a distance of any portion of the at least one signal line from a reference point and information on a position on the object, a signal voltage source that is operatively connectable to each signal line, and a control and evaluation unit that is operatively connectable to each signal line. 
     The method comprises at least steps of:
         by operating the signal voltage source, providing to a signal line a time-dependent measurement signal intended to be traveling along the respective connected signal line,   operating the control and evaluation unit for receiving the measurement signal after being at least partially reflected by at least one portion of the signal line to which the measurement signal has been provided,   operating the control and evaluation unit for determining a position or positions on the object of the portion or portions of the signal line that has or have at least partially reflected the measurement signal,   storing the determined position or positions on the object,   repeating the aforementioned steps for a predetermined number of times for obtaining a plurality of stored successively determined positions on the object,   comparing the obtained plurality of stored successively determined positions on the object with at least one predefined pattern of successive positions to derive a measure of similarity, and   providing an output signal that is indicative of the predefined pattern of successive positions if the derived measure of similarity is lower than a predefined threshold value.       

     The term “signal”, as used throughout this application, shall be understood to mean an electric or electromagnetic signal. The term “(electrically) connected”, as used in this application, shall particularly be understood as being electrically connected by a galvanic connection or a capacitive or inductive coupling. 
     In general, the sensing system for hand positioning detection is based on time-domain reflectometry (TDR), and the provided time-dependent measurement signal intended to be traveling along the respective connected signal line is suitable for TDR measurements. The signal shape of the time-dependent measurement signal may depend on the specific application. 
     The provided time-dependent measurement signal will be traveling along the respective connected signal line and will at least partially be reflected from any impedance discontinuity along the signal line. Such impedance discontinuities can temporarily be generated by a hand or one or more fingers of the hand of an operator of the object, particularly of the steering wheel, being positioned in proximity to the signal line. The nature of the generated impedance discontinuity or impedance discontinuities is determined by the nature of the hand positioning on the object, particularly the steering wheel. 
     With the a priori knowledge about a relation between a distance of any portion of the at least one signal line from a reference point and information on a position on the object, the proposed sensing system is enabled to determine positions of detected impedance discontinuities on the object. This information can be exploited for determining hand positioning scenarios on the object such as hand touch positionings. 
     The proposed method can allow for a high-resolution position detection of a sequence of hand touch positionings, using principles of time-domain reflectometry (TDR). By comparing a plurality of successively determined positions with at least one predefined pattern, recognition of hand gestures that are established by a sequence of hand touch positionings on the object can be accomplished. 
     The hand gestures that are to be recognized by the proposed method can be assigned to a plurality of various additional functions, for instance comfort functions such as multimedia functions. The sequence of hand touch positionings that are establishing a hand gesture may be executed by one hand or by two hands of the operator of the object. The hand touch positionings may include, without being limited to, single-touch positionings with one hand or two hands, multiple touch positionings with one hand or two hands and hand grasp positionings with one hand or two hands. 
     Preferably, the step of comparing includes comparing the obtained plurality of stored successively determined positions to a plurality of predefined patterns of successive positions to derive a measure of similarity for each predefined pattern of the plurality of predefined patterns. In this way, a plurality of hand gestures that are established by different sequences of hand touch positionings on the object can be distinguished and recognized in a reliable manner. 
     Preferably, an execution of the steps of the proposed method can be enabled or disabled by a parameter setting in the sensing system. In this way, the same design of the sensing system can be used with or without the function of hand gesture recognition. Preferably, the parameter setting in the sensing system is designed as a software parameter setting within the control and evaluation unit. 
     In preferred embodiments of the method, the step of repeating the aforementioned steps includes repeating the steps for a predetermined number of times that corresponds to a time period between 0.5 and 1.5 seconds. In this way, high reliability can be achieved for the recognition of the hand gesture. Further, the method can allow for recognition of complex hand gestures that are carried out by an operator or user of the object, particularly the steering wheel within the described time period. 
     Preferably, the object is formed by a rim of a steering wheel, and the at least one predefined pattern of successive positions includes a turning point with regard to a circumferential direction of the rim of the steering wheel. In this way, hand gestures established by hand touch positionings that include wiping back and forth can reliably be detected. 
     In another aspect of the invention, a sensing system for detection of hand gestures established by a sequence of hand touch positionings on an object, particularly a rim of a steering wheel, is provided. 
     The sensing system comprises at least one electrically conducting signal line, a signal voltage source and a control and evaluation unit. 
     The at least one electrically conducting signal line is arrangeable to extend along a part of a surface of the object, particularly the rim of the steering wheel, with a priori knowledge about a relation between a distance of any portion of the at least one signal line from a reference point and information on a position on the object. 
     The signal voltage source is operatively connectable to each signal line and is configured for providing a time-dependent measurement signal to be traveling along the respective connected signal line. 
     The control and evaluation unit is operatively connectable to each signal line and is configured for:
         receiving the measurement signal after being at least partially reflected by at least one portion of the signal line to which the measurement signal has been provided,   determining a position or positions on the object of the portion or portions of the signal line that has or have at least partially reflected the measurement signal,   storing the determined position on the object,   repeating the aforementioned steps for a predetermined number of times for obtaining a plurality of stored successively determined positions on the object,   comparing the obtained plurality of stored successively determined positions on the object with at least one predefined pattern of successive positions to derive a measure of similarity, and   providing an output signal that is indicative of the predefined pattern of successive positions if the derived measure of similarity is lower than a predefined threshold value.       

     The phrase “configured to”, as used in this application, shall in particular be understood as being specifically programmed, laid out, furnished or arranged. 
     The proposed sensing system for hand positioning detection on an object, particularly on a steering wheel, can be of low complexity and can be capable of distinguishing various hand gestures that are each established by a sequence of hand touch positionings on the object. 
     The time-dependent measurement signal can be a pulse signal, as is often used in TDR, but can be a continuous signal as well. In preferred embodiments of the sensing system, the signal voltage source is configured for providing a pulse-shaped signal, a frequency-swept signal, a pseudo random phase-shift keyed signal or a pseudo random signal. This can provide design freedom for appropriately covering a wide range of applications. 
     In the case of a frequency swept sine wave, the control and evaluation unit may be configured to apply a Fast Fourier Transform (FFT) to the received reflected measurement signal. In the case of a pseudo random phase-shift keyed signal or a pseudo random signal, the control and evaluation unit may be configured to apply a cross correlation between the provided measurements signal and the received reflected measurement signal. 
     Preferably, the proposed sensing system forms part of a steering wheel of an automotive vehicle, and the object is formed by a rim of the steering wheel. The term “automotive vehicle”, as used in this patent application, shall particularly be understood to encompass passenger cars, trucks, semi-trailer trucks and buses, although application to other vehicles such as aircrafts or watercrafts is also contemplated. 
     In yet another aspect of the invention, a steering wheel with hand gesture recognition by hand touch positioning detection is provided. The steering wheel comprises an embodiment of the sensing system as disclosed herein, wherein the at least one electrically conducting signal line is arranged to extend along a part of a surface of a rim of the steering wheel. The benefits described in context with the sensing system apply to the proposed steering wheel to the full extent. 
     In particular, the proposed steering wheel is applicable with advantage in the automotive sector; i.e. for use in a vehicle. However, it is also contemplated to employ the proposed steering wheel for aircrafts and sea crafts. 
     In preferred embodiments, the steering wheel further comprises at least one contiguous portion of a rim of the steering wheel that is identifiable, i.e. identifiable to an operator of the steering wheel, by an outer marking, wherein a portion is or portions of the at least one signal line are arranged on the at least one contiguous portion of the rim that is or are employable exclusively for hand gesture recognition, and wherein the at least one contiguous portion defines an interval or intervals of travel time of the measurement signal along the signal line. In this way, the effort of detecting hand touch positionings for hand gesture recognition can be reduced by focusing on the interval or intervals of travel time of the measurement signal that is or are defined by the position of the at least one contiguous portion of the rim. 
     Further, a position on the rim of the steering wheel at which an operator can give input in the manner of a human machine interface (HMI), for instance for selecting or adjusting comfort functions such as multimedia functions, is well-defined and readily identifiable. 
     Preferably, the exclusive employment for hand gesture recognition of the portion or the portions of the at least one signal line and the defined interval or the intervals of travel time is switchable. In this way, the same design of the signal line can be used with or without the function of hand gesture recognition, which can simplify an assembly process of the steering wheel. 
     In preferred embodiments of the steering wheel, the exclusive employment is switchable by a parameter setting in the control and evaluation unit. By that, it can be enabled to incorporate the exclusive employment after mounting the steering wheel or even as part of a retrofit, e.g. an upgrade, without any hardware change. 
     Preferably, the parameter setting in the sensing system is designed as a software parameter setting within the control and evaluation unit, by which the exclusive employment for hand gesture recognition can readily be carried out at any time. 
     In preferred embodiments of the steering wheel, the portion or portions of the at least one signal line that is or are arranged on the at least one contiguous portion of the rim of the steering wheel is or are selectively employable for hand gesture recognition at one point in time, and is or are selectively employable at another point in time as a part of the at least one signal line to be employed in a time domain reflectometry-based measurement of an embodiment of the sensing system disclosed herein to be used for hand positioning detection on the steering wheel. 
     In other words, the at least one signal line can be used as a whole with a suitable sensing system being operated for hand positioning detection (i.e. touch positioning or grasping hand positioning) at one time, and it can be used with a portion or portions of the at least one signal line that are arranged on the at least one contiguous portion of the rim being exclusively employed for hand gesture recognition at another time. In this way, the sensing system and the at least one signal line can be used virtually simultaneously for providing the safety function of Hands-Off Detection and for providing additional functions, for instance comfort functions, such as multimedia functions. 
     In yet another aspect of the invention, a non-transitory, computer-readable medium storing a software module for controlling automatic execution of steps of an embodiment of the method disclosed herein is provided. 
     The method steps to be conducted are converted into a program code of the software module, wherein the program code is implementable in a digital memory unit (such as the computer-readable medium) of the sensing system disclosed herein, and is executable by a processor unit of the sensing system disclosed herein. Preferably, the digital memory unit and/or processor unit may be a digital memory unit and/or a processing unit of the control and evaluation unit of the sensing system. The processor unit may, alternatively or supplementary, be another processor unit that is especially assigned to execute at least some of the method steps. 
     The software module can enable a robust and reliable execution of the method and can allow for a fast modification of method steps. 
     These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. 
     It shall be pointed out that the features and measures detailed individually in the preceding description can be combined with one another in any technically meaningful manner and show further embodiments of the invention. The description characterizes and specifies embodiments of the invention in particular in connection with the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details and advantages of the present invention will be apparent from the following detailed description of not limiting embodiments with reference to the attached drawing, wherein: 
         FIG.  1    schematically illustrates a sensing system in accordance with an embodiment of the invention for detection of hand gestures established by a sequence of hand touch positionings on an object formed by a rim of a steering wheel, in an installed state, 
         FIG.  2    schematically illustrates the electrically conducting signal line of the sensing system pursuant to  FIG.  1   , 
         FIG.  3    schematically illustrates the sensing system pursuant to  FIG.  1    in a scenario with a hand carrying out a gesture established by a sequence of hand touch positionings on the steering wheel, and 
         FIG.  4    is a flow chart of a method of recognizing a hand gesture established by a sequence of hand touch positionings on a steering wheel by operating the sensing system pursuant to  FIG.  1   . 
     
    
    
     In the different figures, the same parts are always provided with the same reference symbols or numerals, respectively. Thus, they are usually only described once. 
     DETAILED DESCRIPTION 
       FIG.  1    schematically illustrates a sensing system for detection of hand gestures established by a sequence of hand touch positionings on an object, which is formed by a steering wheel and, more specifically, by a rim of the steering wheel, in an installed state. For clarity purposes, only the rim  40  or steering ring of the steering wheel  38  is shown, which further comprises at least one spoke that connects the rim  40  to a steering column via a hub in a manner known per se. The steering wheel  38  may be employed in a vehicle designed as a passenger car, but may as well be employed in an aircraft or a watercraft. 
     The sensing system  10  comprises an electrically conducting signal line  12 , a signal voltage source  26  and a control and evaluation unit  28 . 
     The signal line  12  of the sensing system  10  is schematically illustrated in  FIG.  2   . The signal line  12  may be shaped as a meandering pattern, which comprises a plurality of half-circle shaped turns connected by straight-line portions. The signal line  12  may be designed as a coplanar waveguide having an electrically conductive center line and two electrically conductive return lines, which are arranged in an equally spaced manner at both sides of the center line. The center line and the return lines may be attached to a flexible dielectric carrier  14  such as a polymeric foil, for instance by applying a screen printing method. In this way, the signal line  12  is designed to have a predefined uniform characteristic impedance, which can be laid out by varying the geometry and relative positions of the center line and the return lines, as is well known in the art. 
     The flexible dielectric carrier  14  may be backed by an electrically conductive ground plane serving as an additional return line of the coplanar waveguide. 
     The signal line  12  may be open-ended as shown in  FIG.  2   , but it may also be terminated by a lumped impedance that is equal to the characteristic impedance so as to avoid reflections at its end. In the open-ended case a total reflection is to be expected, which can be used as a time reference mark. 
     A maximum dimension between adjacent turning points  16  of the meandering pattern of the signal line  12  is adapted to a circumferential length of a cross-section of the rim  40  of the steering wheel  38  such that a maximum lateral dimension between adjacent turning points  16  of the meandering pattern is more than 25% and less than 50% of a circumferential length of the cross-section of the rim  40  of the steering wheel  38 , and in this specific embodiment may be about 30% of the circumferential length. 
     As shown in  FIG.  1   , the electrically conducting signal line  12  is arranged to extend along a part of a surface of the rim  40  of the steering wheel  38 . The signal line  12  comprises a first section  18 , which is arranged to extend along a part of a surface  20  of the rim  40  of the steering wheel  38  that is facing an operator of the steering wheel  38 , i.e. usually the driver of the vehicle. The signal line  12  further comprises a second section  22 , which is arranged to extend along a part of a surface  24  of the rim  40  of the steering wheel  38  that is facing away from the operator of the steering wheel  38 . The first section  18  and the second section  22  of the signal line  12  are electrically connected in series without an impedance discontinuity. 
     The signal line  12  is installed and arranged on the surface of the rim  40  of the steering wheel  38  with a priori knowledge about a relation between a distance of any portion of the signal line  12  from a reference point  44  and information on a position on the rim  40 . Any point of the signal line  12  may be chosen as the reference point. In this specific embodiment, the reference point  44  is selected to be located at an input end of the signal line  12 . A position of any portion of the signal line  12  on the rim  40  may be defined by specifying the surface, i.e. either the surface  20  facing towards the operator or the surface  24  facing away from the operator, and by specifying a center angle with respect to a zero angle position. 
     The steering wheel  38  further comprises a contiguous portion  46  of the rim  40  that is identifiable by an outer marking to the steering wheel operator. A portion of the signal line  12  is arranged on the contiguous portion  46  of the rim  40  that is employable exclusively for hand gesture recognition. The contiguous portion  46  defines intervals of travel time of the measurement signal along the signal line  12  with regard to the reference point  44 . 
     The signal voltage source  26  is operatively connected to the signal line  12  and is configured for providing a time-dependent measurement signal to be traveling along the connected signal line  12 . In this embodiment, the signal voltage source  26  is designed as an integral part of the control and evaluation unit  28 , sharing the same housing for improved signal processing and control by the control and evaluation unit  28 . In other embodiments, the signal voltage source  26  may be designed as a separate unit with appropriate signal and control lines to the signal line  12  and the control and evaluation unit  28 . 
     In this specific embodiment, the signal voltage source  26  is designed for providing pulse-shaped signals, but in other embodiments, the signal voltage source may be configured for providing a frequency-swept signal, a pseudo random phase-shift keyed signal or a pseudo random signal. 
     The control and evaluation unit  28  is operatively connected to the signal line  12  as well as to the signal voltage source  26 . The control and evaluation unit  28  may comprise a microcontroller that includes a digital data memory unit  32 , a processor unit  30  with data access to the digital data memory unit  32  and a control interface  34 . As will be explained below, the control and evaluation unit  28  is configured for automatic execution of a method of recognizing a hand gesture established by a sequence of hand touch positionings on the steering wheel  38 . 
     The portion of the signal line  12  that is arranged on the contiguous portion  46  of the rim  40  is employable exclusively for hand gesture recognition by a software parameter setting in the control and evaluation unit  28 . By setting the appropriate software parameter, the intervals of travel time of the measurement signal along the signal line  12  that are defined by the contiguous portion  46  of the rim  40  with regard to the reference point  44  will be assigned by the control and evaluation unit  28  to hand gesture recognition. 
     That is to say that the portions of the signal line  12  that are arranged on the contiguous portion  46  of the rim  40  of the steering wheel  38  are selectively employable for hand gesture recognition at one point in time, and are selectively employable at another point in time as parts of the signal line  12  to be employed in a time-domain reflectometry-based measurement of the sensing system  10  to be used for hand positioning detection on the steering wheel for HOD purposes and in particular for distinguishing touch positionings from hand grasping positionings. Due to the speed of operation of the sensing system  10 , this is unnoticeable to the steering wheel operator. 
     If the software parameter was not set appropriately, the portions of the signal line  12  that are arranged on the contiguous portion  46  of the rim  40  of the steering wheel  38  would be employed in the time-domain reflectometry-based measurement of the sensing system at all times to be used for hand positioning detection on the steering wheel  38  for HOD purposes. Thus, the same sensing system hardware can be used to serve both purposes. 
     In the following, an embodiment of the method of recognizing a hand gesture established by a sequence of hand touch positionings on an object formed by the steering wheel  38 , more specifically by the rim  40  of the steering wheel  38 , by operating the sensing system  10  pursuant to  FIG.  1    will be described with reference to  FIGS.  1  and  3   , which schematically illustrates the sensing system pursuant to  FIG.  1    in a scenario with a hand carrying out a gesture established by a sequence of hand touch positionings on the steering wheel, and to  FIG.  4   , which provides a flow chart of the method. In preparation of operating the sensing system  10 , it shall be understood that all involved units and devices are in an operational state and configured as illustrated in  FIG.  1   . 
     In order to be able to automatically execute the method, the control and evaluation unit  28  comprises a software module  36 . The method steps to be conducted are converted into a program code of the software module  36 . The program code is implemented in the digital data memory unit  32  of the control and evaluation unit  28  and is executable by the processor unit  30  of the control and evaluation unit  28 . Alternatively, the software module  36  may as well reside in and may be executable by another control unit of the vehicle, and established data communication means between the control and evaluation unit  28  and the vehicle control unit would be used for enabling mutual data transfer. 
     An execution of the method may be enabled or disabled by an appropriate setting of the software parameter in the control and evaluation unit  28 . 
     In a first step  50  of the method, by operating the signal voltage source  26 , a time-dependent measurement signal is provided to the signal line  12 . The measurement signal is intended to be traveling along the connected signal line  12 . Without any hand positioning on the steering wheel  38  and with the signal line  12  being terminated with a lumped impedance, no reflection is expected at all. The provision of the time-dependent measurement signal may be controlled by the control and evaluation unit  28 . In other embodiments, the provision of the time-dependent measurement signal may be used as a trigger signal for the control and evaluation unit  28  for commencing execution of the following steps. 
     In another step  52  of the method, the control and evaluation unit  28  is operated for receiving the measurement signal after being at least partially reflected by at least one portion of the signal line  12  (also referred to as received reflected measurement signal). 
     In a next step  54 , the control and evaluation unit  28  is operated to determine positions on the rim  40  of the portions of the signal line  12  that have at least partially reflected the measurement signal. This is obtained by using the a priori knowledge about the relation between a distance of any portion of the signal line  12  from the reference point  44  ( FIG.  2   ) and information on a position on the rim  40  ( FIG.  3   ). 
     Due to the software parameter setting in the control and evaluation unit  28 , a determined position on the rim  40  that corresponds to a travel time of the measurement signal that lies within the interval of travel time defined by the contiguous portion  46  of the rim  40  is considered by the control and evaluation unit  28  to be generated by a hand touch positioning on the steering wheel  40  that is part of a sequence of hand touch positionings establishing a hand gesture. 
     In a further step  56  of the method, the determined positions on the contiguous portion  46  of the rim  40  are stored in the digital data memory unit  32 . 
     The described steps  50 - 56  of providing the measurement signal to the signal line  12 , of receiving the measurement signal after being reflected, of determining positions of the portions of the signal line  12  that reflected the measurement signal, and of storing the determined positions are repeated for a predetermined number of times. The predetermined number of times corresponds to a time period that can lie between 0.5 and 1.5 seconds, and that in this specific embodiment may be selected to be 1.0 seconds. During this time, the steering wheel operator may carry out a hand gesture that may include a back and forth wiping gesture on the contiguous portion  46  of the rim  40 . 
     As a result, a plurality of stored successively determined positions on the rim  40  is obtained. In another step  58 , the plurality of stored determined positions is retrieved from the digital data storage unit  32 . In a next step  60 , the plurality of stored determined positions is compared with a predefined pattern of successive positions to derive a measure of similarity. The predefined pattern of successive positions includes a turning point with regard to a circumferential direction of the rim  40 . 
     The derived measure of similarity is compared with a predefined threshold value Thr in another step  62 . If the derived measure of similarity is lower than the predefined threshold value Thr, an output signal is provided by the control and evaluation unit  28  in another step  64  that is indicative of the predefined pattern of successive positions, which in turn is representative of a specific hand gesture. If the derived measure of similarity is equal to or larger than the predefined threshold value Thr, the plurality of stored determined positions is compared with another predefined pattern of successive positions to derive another measure of similarity. This is repeated until the derived measure of similarity is lower than the predefined threshold value Thr for one of the predefined patterns of successive positions, or until the plurality of stored successively determined positions failed to match with any of the predefined patterns of successive positions. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. 
     Other variations to be disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality, which is meant to express a quantity of at least two. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting scope.