Abstract:
The invention relates to a sensor apparatus for a self-propelled floor cleaning appliance for detecting a down step, having a transmission unit and a reception unit for infrared radiation and having evaluation electronics for evaluating the intensity of the radiation received. To develop the sensor apparatus in such a manner that a down step or a steep downslope of the floor surface can be determined more reliably, while the sensor apparatus can be produced at low cost, according to the invention it is proposed that the sensor apparatus has the reception unit and a first and a second transmission unit, the second transmission unit being disposed at a distance from a connecting straight line running through the reception unit and the first transmission unit. The invention also proposes a floor cleaning appliance having a sensor apparatus of this type.

Description:
This application is a continuation of international application number PCT/EP 03/06223 filed on Jun. 13, 2003. 
   The present disclosure relates to the subject matter disclosed in international application number PCT/EP 03/06223 of Jun. 13, 2003 and German application number 102 31 386.5 of Jul. 8, 2002, which are incorporated herein by reference in their entirety and for all purposes. 

   BACKGROUND OF THE INVENTION 
   The invention relates to a sensor apparatus for a self-propelled floor cleaning appliance for detecting a down step with a transmission unit for emitting infrared radiation and a reception unit for receiving infrared radiation and with evaluation electronics for evaluating the intensity of the radiation received. 
   Moreover, the invention relates to a self-propelled and self-steering floor cleaning appliance having a chassis and an electrical drive unit with electrical control unit and drive wheels mounted on the chassis, and with a sensor apparatus of this type. 
   A floor surface can be cleaned with the aid of self-propelled and self-steering floor cleaning appliances without the need for an operator. The floor cleaning appliance is in this case moved along the floor surface that is to be cleaned. If it encounters an obstacle, it changes its direction of movement in accordance with a predeterminable control program. To detect a steep downslope on the floor surface or also a step, the floor cleaning appliance is equipped with a sensor apparatus which detects the floor surface that is to be cleaned by means of infrared radiation and forms a proximity sensor which provides an electrical control signal for the control electronics. If the detected distance exceeds a predetermined maximum permissible distance, the floor cleaning appliance likewise executes a change in the direction of movement. To check the distance, the sensor apparatus has a transmission unit which directs infrared radiation onto the floor surface. The infrared radiation which is reflected from the floor surface is received by the reception unit, and the intensity of the reflected radiation is evaluated by the evaluation electronics. 
   Sensor apparatuses of this type have the difficulty that the intensity of the reflected infrared radiation is dependent not only on the distance between the sensor apparatus and the floor surface, but also on the direction of the radiation reflected from the floor surface. If the floor surface has regions with a reflection surface oriented obliquely with respect to the sensor apparatus, for example in the form of cables or beveled edge regions of floor tiles, the infrared radiation emitted is reflected in a direction away from the reception unit, so that a signal of weak intensity is received even when the true distance is only relatively short. 
   It has already been proposed to use a position-dependent reception unit, in which case it is not the intensity of the reflected radiation that is evaluated, but rather the point of impingement of the infrared radiation on the reception unit. This point of impingement is dependent on the distance between the sensor apparatus and the floor surface that is to be cleaned. However, position-dependent sensor apparatuses of this type are characterized by considerable production difficulties and are therefore associated with by no means insignificant production costs. 
   It is an object of the present invention to develop a sensor apparatus and a floor cleaning appliance of the type described in the introduction in such a manner that a down step or a steep downslope in the floor surface can be detected more reliably, and the sensor apparatus can be produced at low cost. 
   SUMMARY OF THE INVENTION 
   In a sensor apparatus of the generic type, this object is achieved, according to the invention, by the fact that the sensor apparatus has a reception unit and a first and a second transmission unit, the second transmission unit being disposed at a distance from a connecting straight line running through the reception unit and the first transmission unit. 
   According to the invention, two transmission units are used, with the aid of which infrared radiation can be directed onto the floor surface that is to be cleaned, and the infrared radiation which is in each case reflected is received by the common reception unit and converted into an electrical signal which is fed to the evaluation electronics, which evaluates the intensity of the infrared radiation reflected. The radiation emitted by the second transmission unit and reflected from the floor surface impinges on the reception unit at a different angle from the radiation emitted by the first transmission unit and reflected by the floor surface. For this purpose, the second transmission unit is disposed at a distance from a connecting straight line which is defined by the reception unit and the first transmission unit. It has been found that by using this type of arrangement of two transmission units and one common reception unit, it is possible to reliably detect a down step or a steep downslope in the floor surface by evaluating the intensity of the reflected radiation. This allows a reliable conclusion to be drawn as to whether the distance between the sensor apparatus and the floor surface is within a tolerable distance range, so that the floor cleaning appliance can move onward in the same direction of travel, or is outside this tolerance range, in which case there is a risk of the floor cleaning appliance falling, so that it is necessary for the floor cleaning appliance to change its direction of travel, even in regions with cables running on the floor and/or surface portions oriented obliquely with respect to the vertical, in the form of beveled edge regions of floor tiles. 
   To achieve a configuration of the sensor apparatus which is compact and simple to handle in particular for assembly purposes, it is expedient if the reception unit and the first and second transmission units are integrated in a housing of the sensor apparatus. 
   It is particularly advantageous if the first and second transmission units focus the infrared radiation which is emitted in each case into a common focal point. It has been found that with an orientation of the infrared radiation of this nature, it is possible to draw a particularly reliable conclusion as to whether the distance between the sensor apparatus and the floor surface exceeds a predeterminable maximum value such that there is a risk of the floor cleaning appliance falling. 
   A preferred embodiment is distinguished by the fact that the second transmission unit is disposed between the reception unit and the first transmission unit, with respect to the connecting straight line. As a result, the sensor apparatus acquires a particularly compact configuration. In this context, it is particularly advantageous if the distance between the reception unit and the first transmission unit is greater than the distance between the second transmission unit and the connecting straight line. 
   An embodiment of the sensor apparatus according to the invention which can be produced at particularly low cost is distinguished by the fact that the first and second transmission units each have an infrared radiation source and an optical element for beam guidance, in particular for focusing the emitted radiation, the radiation sources being oriented parallel to one another. An embodiment of this type is distinguished by simple assembly of the sensor apparatus. 
   It is advantageous if the reception unit comprises an element which is sensitive to infrared radiation and has associated with it an optical element for beam guidance. The beam guidance element may in this case be configured as a diverting and/or focusing element which diverts the reflection radiation impinging on the beam guidance element toward the radiation-sensitive element and focuses it onto the element. 
   It is preferable for optical elements for background masking to be associated with the reception unit. This makes it possible to block out background rays and therefore facilitates evaluation of the received signal. The elements for background masking may be integrated in the elements for beam guidance. 
   Preferably, the reception unit and the first and second transmission units are disposed at a distance from one another, with an optical separating element which is opaque to radiation in each case being disposed between the reception unit and the first transmission unit and between the reception unit and the second transmission unit. Separating elements of this type make it possible to ensure that infrared radiation which is emitted by the transmission units cannot impinge directly on the reception unit, but rather must firstly be reflected from the floor surface that is to be cleaned. 
   A structurally particularly simple embodiment is distinguished by the fact that the two separating elements form a single-piece partition made from a material which is opaque to infrared radiation. The partition may in this case be formed integrally on the housing of the sensor apparatus. It is particularly advantageous if the partition forms a support for the reception unit and for the first and second transmission units. This enhances the mechanical stability of the sensor apparatus. 
   As was mentioned in the introduction, the invention also relates to a self-propelled and self-steering floor cleaning appliance having a chassis and having an electrical drive unit which comprises electrical control electronics and drive wheels mounted on the chassis. To develop the floor cleaning appliance in such a manner that the risk of it falling can be reliably detected, according to the invention it is proposed that the floor cleaning appliance comprises a sensor apparatus of the type described above, which is coupled to the control electronics, the infrared radiation which is emitted being directed onto the floor surface that is to be cleaned. 
   As has already been mentioned, by using the sensor apparatus, which can be produced at low cost, it is possible to reliably detect the risk of the appliance falling, i.e. the evaluation electronics can check whether the distance between the sensor apparatus and the floor surface that is to be cleaned exceeds a permissible maximum value. 
   The floor cleaning appliance preferably has two drive wheels, a sensor apparatus being disposed in front of and behind each drive wheel, based on a main direction of movement of the floor cleaning appliance. This makes it possible to reliably detect the risk of the floor cleaning appliance falling both when it is moving forward and when it is moving backward. 
   To ensure that the risk of the floor cleaning appliance falling can be detected not only when the front of the appliance is approaching a change in height, but also when the change in height is being approached at an acute angle, in a particularly preferred embodiment of the floor cleaning appliance according to the invention it is proposed that the front and rear sensor apparatuses which are respectively associated with a drive wheel are oriented with their respective connecting straight lines aligned with one another. 
   It is particularly advantageous if the front and rear sensor apparatuses, respectively associated with a drive wheel, are oriented with their respective connecting straight lines aligned with the tread of the drive wheel. 
   The floor cleaning appliance preferably comprises at least one supporting roller which is disposed between the front sensor apparatuses and the drive wheels, based on a main direction of movement of the floor cleaning appliance. In this context, it is particularly expedient if the distance between the supporting rollers and the front sensor apparatuses, as seen in the main direction of movement, corresponds to at least a quarter of the distance between the front sensor apparatuses and the drive wheels. This makes it possible to ensure that the floor cleaning appliance can be stopped in good time when the floor cleaning appliance is approaching a down step before the supporting roller, which is positioned in front of the drive wheels in the direction of movement, moves beyond the edge of the step. 
   The following description of a preferred embodiment of the invention, in conjunction with the drawing, serves to provide a more detailed explanation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1 : shows a diagrammatic view of a floor cleaning appliance according to the invention from below; and 
       FIG. 2 : shows an enlarged illustration of region A from  FIG. 1  with a sensor apparatus according to the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  diagrammatically depicts a view of a self-propelled and self-steering floor cleaning appliance, which is denoted overall by reference numeral  10 , from below. The floor cleaning appliance comprises a housing  12 , which forms a chassis  14 , onto the top side of which a housing cover (not shown in the drawing) can be fitted. Two drive wheels  16 ,  18 , which each have a tread  17  and  19 , respectively, by means of which the drive wheels  16 ,  18  are in contact with a floor surface that is to be cleaned, are rotatably mounted on the chassis  14 . 
   The drive wheels  16 ,  18  each have an associated electric drive motor  21  and  23 , respectively, which is fixed to the underside of the chassis  14 . The two drive motors  16 ,  18  are electrically connected to control electronics  25 , positioned on the top side of the chassis  14 , and to a rechargeable battery, which is known per se and is therefore not shown in the drawing. 
   On its top side, the chassis  14  carries a suction unit, which is known per se and therefore not illustrated in the drawing and which is in flow communication in conventional manner, via a suction passage, with a dirt inlet opening  28  disposed at a base plate  15 , a dirt collection vessel (not shown) being disposed in conventional manner between the dirt inlet opening  28  and the suction unit. 
   A brush roller  30  is rotatably mounted in the region of the dirt inlet opening  28 . The brush roller  30  comprises radially protruding sweeping brushes  32  which pass through the dirt inlet opening  28  and with the aid of which dirt can be picked up from a floor surface that is to be cleaned and can be thrown through the dirt inlet opening  28  into the suction duct. The axis of rotation  34  of the brush roller  30  is oriented perpendicular to a longitudinal axis  36  of the floor cleaning appliance  10  and is positioned at a distance in front of the drive wheels  16  and  18 , based on a main direction of movement, symbolized by the arrow  38 , of the floor cleaning appliance. 
   Two supporting rollers  40 ,  42 , the axis of rotation of which is oriented parallel to the axis of rotation  34  of the brush roller  30  and parallel to the common axis of rotation  44  of the drive wheels  16  and  18 , are freely rotatably mounted on the base plate  15 , behind the dirt inlet opening  28 , based on the main direction of movement  38 , and mirror-symmetrically with respect to the longitudinal axis  36 . 
   The floor cleaning appliance  10  can be moved forward in the main direction of movement  38  and backward in the opposite direction to this direction  38  by means of the drive wheels  16  and  18  and the supporting rollers  40 ,  42 . In this way, dirt can be sucked up from the floor surface that is to be cleaned under the action of the suction flow generated by the suction unit, with the brush roller  30  additionally being used to pick up dirt. Actuation of one of the two drive motors  21  or  23  on one side allows the floor cleaning appliance  10  to be turned. 
   If the floor cleaning appliance  10  approaches a down step or some other form of steep downslope in the floor surface that is to be cleaned, a step or downslope of this type is detected by the floor cleaning appliance  10 , which then changes its direction of movement in order to prevent the floor cleaning appliance from falling. For this purpose, a total of four sensor apparatuses  50 ,  51 ,  52 ,  53  are mounted on the underside of the housing  12 , the sensor apparatuses  50  and  51  being associated with the drive wheel  16  and the sensor apparatus  50  being disposed in front of the drive wheel  16  and the sensor apparatus  51  behind the drive wheel  16 , based on the main direction of movement  38 . The sensor apparatuses  52  and  53  are associated with the drive wheel  18  in a corresponding way, with the sensor apparatus  52  being positioned in front of the drive wheel  18  and the sensor apparatus  53  behind the drive wheel  18 , based on the main direction of movement  38 . The distance between the housing  12  and the floor surface that is to be cleaned can be recorded contactlessly by means of the sensor apparatuses  50  to  53 . If the distance exceeds a predetermined maximum value, the floor cleaning appliance  10  stops in order then to continue its movement in the opposite direction. 
   The sensor apparatuses  50  to  53  are of identical configuration. Consequently, the following text will provide a more detailed description only of the sensor apparatus  50 , which is diagrammatically depicted in  FIG. 2 . It comprises a sensor housing  55 , which surrounds a first transmission unit  57  and a second transmission unit  59 , with the aid of which in each case focused infrared radiation can be directed obliquely with respect to the vertical onto the floor surface that is to be cleaned, and also a common reception unit  61  for receiving infrared radiation reflected from the floor surface and for providing an intensity-dependent electrical signal. 
   In each sensor apparatus  50  to  53 , the respective reception unit  61  is connected via a signal line  63  to evaluation electronics  65  which are integrated in the control electronics  25  and evaluate the electrical signals provided in accordance with the intensity of the infrared radiation received in a manner which is conventional and therefore not explained in more detail in the present context, and provide an alarm signal to the control electronics  25  in the event of a maximum distance between housing  12  and floor surface that is to be cleaned being exceeded, so that the movement of the floor cleaning appliance is stopped and then continued in the opposite direction of travel. The reception unit  61 , in combination with the first transmission unit  57 , defines a connecting straight line  67 , and the second transmission unit  59  is disposed at a distance from the connecting straight line  67  and between the reception unit  61  and the first transmission unit  57  with respect to the connecting straight line  67 . 
   The first transmission unit  57  and the second transmission unit  59  are identical in configuration and each comprise an infrared radiation source in the form of a diode  69  which emits infrared light and an optical focusing element  71  for focusing the infrared radiation emitted by the light-emitting diode  69 . The focused radiation from the light-emitting diodes  69  of the two transmission units  57  and  59  is bundled in a common focal point. 
   The reception unit  61  has an element which is sensitive to infrared light, in the form of a phototransistor  73 , which likewise has an optical focusing element  75  connected upstream of it, which diverts the infrared radiation impinging on the reception unit  61  in the direction of the phototransistor  73  and focuses it onto the phototransistor  73 . 
   A housing insert  77  made from a material which is opaque with respect to infrared radiation is disposed between the reception unit  61  and the first and second transmission units  57  and  59 , respectively. The housing insert  77  in this case forms a mechanical support for the transmission and reception units  57 ,  59  and  61  and comprises a housing wall  78  which is of single-piece configuration and against which the reception unit  61  and the first transmission unit  57  and the second transmission unit  59  rest really, and which, moreover, ensures that infrared radiation emitted by the transmission units  57  and  59  cannot reach the reception unit  61  directly. 
   Since the second transmission unit  59  is disposed obliquely with respect to the connecting straight line  67 , the beams emitted by the transmission units  57  and  59  and reflected from the floor surface impinge on the reception unit  61  at different angles. It has been found that using an orientation of this nature ensures that cables running on the floor surface or obliquely oriented reflection surfaces, for example beveled edge regions of floor tiles, have no adverse effect on the checking of the risk of the floor cleaning appliance falling. 
   As is clear from  FIG. 1 , the sensor apparatuses  50 ,  51  and  52 ,  53  which are respectively associated with a drive wheel  16  and  18  are oriented with their connecting straight lines  67  aligned with one another and aligned with the respective tread  17  or  19  of the associated drive wheels  16  or  18 , respectively. The front sensor apparatuses  50  and  52 , based on the main direction of movement  38 , are disposed at the level of the axis of rotation  34  of the brush roller  30 , based on the longitudinal axis  36 , so that the supporting rollers  40  and  42  are positioned between the front sensor apparatuses  50  and  52  and the drive wheels  16 ,  18 , based on the longitudinal axis  36 . The distance between the supporting rollers  40 ,  42  and the front sensor apparatuses  50 ,  52 , based on the longitudinal axis  36 , is in this case approximately one third of the distance between the common axis of rotation  44  of the drive wheels  16  and  18  and the front sensor apparatuses  50  and  52 . 
   If the floor cleaning appliance  10  is displaced in the main direction of movement  38 , the front sensor apparatuses  50  and  52 , in combination with the evaluation electronics  65 , detect that a maximum distance between the housing  12  and the floor surface that is to be cleaned has been exceeded if a down step is reached. The result of this is that the movement of the floor cleaning appliance  10  is stopped even before the supporting rollers  40  and  42  reach the step that has been detected by the sensor apparatuses  50  and  52 . Then, the direction of movement of the floor cleaning appliance  10  is reversed, so that the floor cleaning appliance  10  moves away from the step again. If a step or steep downslope in the floor surface is detected by only one of the sensor apparatuses  50 ,  51 ,  52 ,  53 , the floor cleaning appliance  10  executes a turning movement in the direction away from the step.