Method for determining the rotational speed of a spray arm of a dishwasher

Abstract

Method for determining the rotational speed of a spray arm (18) of a dishwasher (1), in which images are taken of the interior (3) of a washing container (2) of the dishwasher (1) housing the spray arm (18) by means of a camera (7), which are then processed for evaluation and subsequently compared with each other, and in which the rotational speed of the spray arm (18) is calculated as a function of the result of the image comparison.

Description

Method for determining the rotational speed of a spray arm of a dishwasher

[0001] The invention relates to a method for determining the rotational speed of a spray arm of a dishwasher.

[0002] Dishwashers as such are well known from the state of the art, which is why a separate printed proof is not required at this point.

[0003] Dishwashers typically have a wash chamber. This chamber is accessible to the user via a loading opening, which can be sealed fluid-tight by means of a pivoting wash chamber door. Under normal use, the wash chamber serves to hold items to be cleaned, such as dishes, cutlery, and / or the like.

[0004] To spray the items to be cleaned with cleaning fluid, the so-called wash liquor, the dishwasher has a spray system inside the wash tub. This spray system provides rotatably mounted spray arms, typically two or three of which are provided. Under normal operating conditions, the items to be cleaned are sprayed with the wash liquor by means of rotating spray arms.

[0005] Dishwashers typically use racks for loading items to be cleaned. These racks are designed to be pulled out of the wash tub by the user. In a preferred embodiment, two such racks are provided, positioned one above the other in the wash tub, oriented vertically. Each rack is typically equipped with a spray arm. Another common embodiment includes a cutlery drawer in addition to the two racks. This drawer is intended for holding cutlery items to be cleaned. A spray arm can also be attached to such a cutlery drawer.

[0006] To achieve the desired cleaning result, it is essential that the spray arms of the spray system rotate as intended during operation. If this rotation fails, the items being cleaned cannot be properly exposed to the cleaning solution. Possible reasons for the spray arm not rotating include, for example, an insufficient amount of cleaning solution, a blockage of the spray arm by items incorrectly placed in the wash tank, and / or similar issues. To remedy this, it is known in the prior art to implement spray arm speed sensing. This is preferably done using a Hall sensor, which is installed in each spray arm to be monitored.

[0007] A dishwasher with a Hall sensor for detecting the speed of the spray arm is disclosed in DE 101 21 083 A1.

[0008] Spray arm speed sensing using a Hall sensor has proven effective in everyday practical use. However, there is still room for improvement.

[0009] Measuring the rotational speed of a spray arm mounted on the upper rack using a Hall sensor has proven particularly complex, especially with height-adjustable upper racks. The height adjustability of the upper rack necessitates a very sophisticated Hall sensor, which is highly sensitive and expensive. Furthermore, the Hall sensor cannot detect any other operating conditions of the dishwasher besides the spray arm speed, making the use of other sensors essential. The number of sensors used increases not only the cost but also the potential for errors. Therefore, there is a constant effort to minimize the number of sensors used for monitoring the dishwasher's functionality.

[0010] US Patent 6,263,888 B1 discloses a dishwasher with a video camera that captures the movement of a satellite spray arm and monitors its chaotic movement to ensure sufficiently chaotic behavior of the spray arm.

[0011] Against the background explained above, the object of the invention is to provide a new method for determining the rotational speed of a spray arm of a dishwasher, which is easy to use and also reliable in operation while minimizing costs.

[0012] To solve this problem, the invention proposes a method for determining the rotational speed of a spray arm of a dishwasher, in which images are created from the interior of a washing container of the dishwasher housing the spray arm using a camera, which are then processed for evaluation and subsequently compared with each other, and in which the rotational speed of the spray arm is calculated as a function of the result of the image comparison.

[0013] For the purpose of determining the rotational speed, a camera is used as a sensor instead of a Hall sensor, according to the invention. During normal operation of the dishwasher, this camera takes pictures of the interior of the dishwasher's wash tub. These images are then processed for evaluation and subsequently compared. The image comparison allows for a conclusion to be drawn about the rotational speed of the monitored spray arm, which is calculated based on the results of the image comparison.

[0014] Compared to the previously known Hall sensor, the inventive method for determining rotational speed using a camera is characterized by essentially two advantages. Firstly, the sensor design is comparatively simple and therefore less susceptible to interference. In particular, sensing is independent of the position of a height-adjustable upper basket. Secondly, the camera can be used not only for determining rotational speed. Other operating states of the dishwasher can also be sensed using the camera provided according to the invention, for example, the load status of the dishwasher and / or the degree of soiling of the items to be cleaned. Thus, the camera can perform a multiple sensory tasks. This results in a cost reduction because, on the one hand, the use of comparatively complex Hall sensors can be avoided and, on the other hand, the total number of sensors used can be reduced.Minimizing the number of sensors also reduces the risk of failure.

[0015] The load detection according to the prior art is determined indirectly using the circulation pump based on a stable pump operation. For this purpose, several small amounts of water are added to the dishwasher after the water intake step. Once the minimum water quantity required for stable pump operation is reached, the water intake is stopped. This known method of load detection is comparatively time-consuming and has the disadvantage that the unstable pump operation until stable operation is achieved is audibly perceptible, which can be perceived as unpleasant by the user. Furthermore, this known indirect load detection method cannot differentiate between the type of dishes and / or their position within the wash chamber.

[0016] The camera used according to the inventive method provides a solution here. In addition to sensing the spray arm speed, it makes it possible to perform direct load detection, whereby the type of load and its placement within the washing chamber can also be detected.

[0017] Load detection using cameras is not unknown in the prior art. For example, DE 100 48 081 A1 discloses a method for detecting the load of dishes being washed using an image recognition system. According to this method, an image of the actual load is captured and compared with a reference image stored in the dishwasher's program control. However, spray arm rotation detection is not possible with the method disclosed in DE 100 48 081 A1, and certainly not a combined detection of spray arm speed and load status. Furthermore, the results of the known method regarding load detection depend on the quality of the reference image that is stored beforehand. Therefore, it is specifically not possible with the method disclosed in DE 100 48 081 A1 to differentiate between individual load states.

[0018] The invention proposes a method for determining the rotational speed of a spray arm, which is comparatively simple and reliable thanks to the use of a camera. Furthermore, the camera can also be used as a sensor to detect other operating states of the dishwasher, thus creating a synergistic effect. The method according to the invention involves using the camera to capture images of the interior of the dishwasher's wash tub that houses the spray arm. These images are then analyzed, and the result of this analysis is used to calculate the rotational speed of the spray arm captured by the camera.

[0019] Images captured by the camera can be transmitted to a user-defined display device, such as a smartphone, PC (especially a tablet), or similar device, via a communication connection such as Wi-Fi. This ability to transmit images to a user-defined device can be particularly useful for the dishwasher manufacturer's customer service department to support on-site troubleshooting.

[0020] The invention further provides that an image captured by the camera of the interior is reduced to a section depicting the spray arm area. This process step thus involves a reduction of the image size. The image captured by the camera is reduced in size to the image area necessary for determining the rotational speed, i.e., the image area depicting the spray arm to be sensed. This image reduction step advantageously reduces subsequent image evaluation time and ultimately leads to more reliable process execution, as image areas that could potentially influence the calculation and are irrelevant for determining the rotational speed are eliminated. Only the section of the captured image showing the spray arm is used to determine the spray arm rotational speed, so the image to be evaluated subsequently can be reduced to this section.

[0021] According to a further feature of the invention, an image is processed by changing its color, contrast, saturation, and / or the like. Such image processing serves to easily generate image-technical comparison parameters and, based on these, to reliably perform a simplified comparison. Thus, according to the invention, the comparison is not between images that reproduce the photographed interior 1:1, but rather between images that, due to their targeted processing and the resulting specific image characteristics, enable a simplified and, above all, faster comparison.

[0022] According to a first alternative method implementation, the images are to be acquired at a predetermined frequency, preferably below 25 Hz. A possible image acquisition frequency is, for example, 5 Hz. Accordingly, five images are acquired per second.

[0023] The generated images are processed as previously described, for example, by adjusting appropriate brightness and contrast values, followed by black and white image generation. An image processed in this way has areas that can be clearly assigned to be either light or dark. The number of pixels representing the light and dark areas of an image is summed according to another feature of the method, and the sums are plotted on a curve diagram. In this way, the changing proportion of dark to light areas, and vice versa, over time can be recorded in a curve diagram. Based on recurring area patterns, the spray arm speed can then be calculated from the curve of the curve diagram, according to another feature of the method.

[0024] Preferably, to increase the safety of the process, an area analysis is performed for each image, both for a first half of the image and for a second half of the image, whereby the two halves are determined based on the axis of rotation of the spray arm captured by the image.

[0025] According to a second alternative of the method according to the invention, continuous image generation, preferably with a frequency of at least 25 Hz, is carried out with simultaneous interior illumination in a flashing light mode with a variable, predefinable frequency.

[0026] According to this method, image generation occurs with an increased image generation frequency of at least 25 Hz, in contrast to the previously described variant. Thus, continuous image generation takes place.

[0027] The dishwasher's interior lighting operates in flash mode during image acquisition. The flash frequency is variable and continuously adjusted by the dishwasher's program control in preferably frequency-equidistant steps. This results in stroboscopic illumination of the interior, which, at the appropriate stroboscopic frequency, produces a "static" image captured by the camera. The spray arm speed can then be calculated from the flash frequency set at the moment the "static" image is captured. Thus, successively acquired images are compared, and if they match, the spray arm speed can be calculated based on the flash frequency.

[0028] According to a further feature of the invention, an image comparison is performed with a previously created reference image stored in the dishwasher's control system. Such a reference image comparison can be used to perform load detection. The camera, which serves as a sensor for determining the spray arm position, thus also enables load detection. For example, an image showing an empty wash chamber serves as the reference image. The created image of the current state is compared with this reference image, with the resulting cross-sectional image providing an assessment of the percentage of the wash chamber's capacity and thus the load status.

[0029] Preferably, both the reference image and the image showing the current state are divided into zones, enabling zone-wide estimation. This allows not only the determination of the percentage of loading, but also the identification of which zones within the predefined zones are loaded and to what extent.

[0030] Furthermore, comparing cross-sectional images allows for differentiating the load status according to the type of dishware being washed. For example, image processing allows for the differentiation between transparent and opaque items. Thus, a distinction can be made between porcelain and glassware.

[0031] This possibility of differentiated load detection makes it possible to adjust the spray arm speed to the specific load condition. Using the method according to the invention, continuous monitoring of the spray arm speed is possible, so that adjustments can be made during the ongoing rinsing process if deviations are detected. The method according to the invention thus enables effective spray arm speed control depending on the detected load condition.

[0032] According to a further feature of the invention, the rotational speed of another spray arm is determined acoustically. For this purpose, a camera equipped with microphones is preferably used.

[0033] Using the method according to the invention, the middle spray arm is preferably sensed. The lower and upper spray arms are not imaged. Their rotational speed can be monitored using the microphones integrated into the camera, with audio evaluation taking place. When the middle spray arm is switched off, the acoustic signal from the other two spray arms can be easily filtered out from the other noises generated in the washing chamber.

[0034] Further features and advantages of the invention will become apparent from the following description with reference to the figures. These show: Fig. 1 Schematic sectional view from the front of a washing container of a dishwasher according to the invention; Fig. 2 in a schematic representation from the front, the rinsing container Fig. 1 with the dishwasher door open; Fig. 3 an image of the interior of the washing container created by a camera in accordance with the method according to the invention; Fig. 4. The image after Fig. 3 in a prepared presentation; Fig. 5a in schematic representation from the front the washing container with a spray arm in a first position; Fig. 5b in schematic representation from the front the washing container with a spray arm in a second position Fig. 5c in schematic representation from the front the washing container with a spray arm in a third position; Fig. 6 in schematic sectional view from the side the rinsing container after Fig. 5 with the dishwasher door closed; Fig. 7 in schematic sectional view from the side the rinsing container after Fig. 5 with the dishwasher door open; Fig. 8 the representation of the rinsing container according to Fig. 7 with cutlery drawer extended; Fig. 9 the representation of the rinsing container according to Fig. 7 with the upper basket extended; Fig. 10 the representation of the rinsing container according to Fig. 7 with the lower basket extended; Fig. 11 in a block diagram the implementation of the inventive process according to a first alternative; Fig. 12 a after the procedure according to Fig. 11 created curve diagrams; Fig. 13 in a block diagram the implementation of the inventive process according to a second alternative; Fig. 14 in a schematic top view from the front the washing container in a representation with unblocked spray arm and in a representation with blocked spray arm; Fig. 15 in a block diagram the implementation of the inventive process according to a third alternative; Fig. 16 in a schematic representation a load detection divided into zones and Fig. 17. Based on two curve diagrams, a rinse liquor application rate of the items to be cleaned is set based on a detected load detection.

[0035] Fig. Figure 1 shows a schematic sectional view from the front of a wash tub 2 of a dishwasher 1, which is not shown in detail otherwise. The wash tub 2 defines an interior space 3, the so-called wash chamber. This is accessible from the user via a loading opening 4, which can be closed in a fluid-tight manner by means of a door 5 that is rotatably arranged on the wash tub 2.

[0036] In its intended use, the washing chamber 3 serves to hold items 11 to be cleaned, which may include, for example, plates 12, pots and pans 13 and other dishes 14, such as glasses, bowls, saucers and the like, as can be seen in particular from the illustration according to Fig. 2 results.

[0037] For the intended purpose of accommodating items to be cleaned 11, the dishwasher 1 in the illustrated embodiment has a lower basket 8, an upper basket 9 and a cutlery drawer 10.

[0038] For the purpose of applying washing solution to the items to be cleaned 11, the dishwasher 1 has a spray device 15. This is connected in terms of flow to a circulation pump 16 of the dishwasher 1, by means of which the spray device 15 is supplied with washing solution.

[0039] In the illustrated embodiment, the spray device 15 has three spray arms: an upper spray arm 17, a middle spray arm 18, and a lower spray arm 19. Under normal operating conditions, the cleaning solution pumped by the circulation pump 16 is directed to the spray arms 17, 18, and 19 of the spray device 15, from where it is then applied to the items 11 to be cleaned. The spray arms 17, 18, and 19 are each rotatably arranged in a manner known per se and rotate under normal operating conditions.

[0040] As can be seen in particular from the presentation according Fig. As shown in Figure 2, the dishwasher 1 according to the invention has a camera 7 which is arranged on the inside 6 of the door 5. The camera 7 is positioned such that, when the door 5 is closed as intended, it is opposite the middle spray arm 18, i.e., the camera image captures, in particular, the middle spray arm 18, as can be seen from a combination of, in particular, the Fig. 3 and Fig. 6 results.

[0041] Fig. Figure 3 shows an image of the washing chamber 3 taken by camera 7. The items to be cleaned 11 and the middle spray arm 18 are clearly visible.

[0042] Fig. Figure 4 shows the image created by camera 7 according to Fig. 3 in a restored state. The original camera image after Fig. Image 3 was then modified with respect to contrast and saturation and converted into a black and white image. The result of this image processing is a comparison image, which is subsequently used for the implementation of the method according to the invention and, thanks to the processing, has clearly identifiable white areas on the one hand and black areas on the other.

[0043] Fig. Figure 5 shows a schematic top view from the front of the washing container 2 of the dishwasher 1, wherein the Fig. 5a, Fig. 5b and Fig. 5c each represent different positions of the middle spray arm 18.

[0044] The inventive method for determining the rotational speed of the middle spray arm 18 is described in Fig. Figure 11 is shown schematically, illustrating a first alternative procedure.

[0045] Using camera 7, 2 images are taken of the interior 3 of the rinsing tank housing the spray arm 18, according to Fig. 3. The image creation frequency is, for example, 5 Hz. The lighting device already present in the washing tank 2 serves as interior lighting for image creation.

[0046] The images created by the camera are then processed for evaluation, whereby they are converted into a black and white image and contrast and saturation are adjusted, so that comparison images can be produced according to the diagram. Fig. 4 will be created.

[0047] In a further process step, the comparison images are reduced to those image sections that show the central spray arm 18. Thus, those image sections that are not required for a given spray arm rotation speed are cropped out.

[0048] Alternatively, according to process step 3a, the upper and lower image areas could be used for soiling detection and / or for spray arm blockage detection, which will be described below.

[0049] In the next step of the process, the number of pixels representing the light and dark areas of each comparison image is summed up, and the sums are transferred to a curve diagram according to a 5th process step.

[0050] According to an alternative procedure according to process step 4a, pixel summation can also take place for only one spray arm half, as shown in the illustration. Fig. Figure 11 shows that, instead of considering the area to create the curve diagram, the determined maxima and minima could also be used as values ​​according to a procedural alternative as described in step 5a.

[0051] The result of the 5th process step is a curve diagram, as shown separately in Fig. 12 is reproduced.

[0052] Using the curve diagram, the rotational speed of the spray arm 18 can be derived according to the 6th process step by, for example, considering the area, so that a calculation of the spray arm rotational speed per minute can then be carried out in a 7th process step.

[0053] Fig. 12 shows, based on the exemplary spray arm positions of the Fig. 5a, Fig. 5b and Fig. 5c recognize how the curve progression is represented in detail. The rotational speed of the spray arm 18 is determined as the distance between two comparison images on the time axis that are identical with respect to their black / white distribution. In Fig. 12 This time interval is illustrated by the example of the recurring spray arm positions after Fig. 5a shown.

[0054] The method described above is used to determine the rotational speed of the central spray arm 18 during normal operation in a simple manner. The method is performed while the circulation pump 16 is running. After switching on the camera 7 and the corresponding interior lighting in step 1, image processing follows in step 2. This serves to normalize the camera's field of view and / or to simplify the evaluation image for a subsequent calculation algorithm. For spray arm speed detection, each captured image is reduced to the essentials, as can be seen from a comparison of the images from step 2 to step 3 according to the Fig. 3 and Fig. This results in step 4. Here, only a highly simplified, narrow image section is used to depict the movement path of the spray arm 18. In step 4, the image section of the spray arm movement path is divided into two halves. Depending on the spray arm position, different brightness gradients result from the right and left spray arm wings. These are clearly visible due to the processed image from step 2, with black (dark) and white (light) areas (pixels), and are very easy for an electronic evaluation unit to recognize. This property is used to convert the actual spray arm rotation into a simplified diagram curve. For this purpose, the light and dark points for the respective spray arm halves are preferably summed. A possible converted area gradient for one spray arm half in a simplified diagram representation is shown in the previously explained... Fig. 12 shown.

[0055] One alternative procedure shows Fig. 13. According to this method, flashes of light are emitted at adjustable time intervals, causing movements to appear jerky as a sequence of still images in a dark environment. For this purpose, the interior lighting is operated like a strobe light, with the flash frequency corresponding to the illustration shown. Fig. 13 is being followed.

[0056] In accordance with the procedural alternative already explained above, Fig. 11 will also be carried out according to the procedural variant according to Fig. 13. In a first process step, images are created, which are then processed in a second process step to simplify the process. In contrast to the process variant according to Fig. However, in the procedure variant 11, this occurs according to Fig. 13 continuous image acquisition with a frequency of at least 25 Hz.

[0057] The third step of the process involves comparing successively created images. If this comparison reveals a lack of image identity according to step 4, the light flash duration is adjusted according to step 4a.

[0058] However, if the image comparison according to process step 4 results in an image identity, the spray arm speed can be calculated using the given light flash time according to process step five.

[0059] Preferably, a spray arm standstill check is performed according to process step 5a by varying the time required for one spray arm revolution. If the resulting comparison images remain identical, the spray arm 18 is at a standstill.

[0060] According to process step 6, the dishwasher control system can be queried to determine whether the middle spray arm 18 is being filled with dishwashing liquid. If so, the middle spray arm 18 rotates as intended, and the previously determined rotational speed is correct. According to process step 7, the measurement can then be ended, and the camera and light can be switched off.

[0061] According to the invention, a camera 7 is used to determine the spray arm speed in the process. This camera can also be used to perform load detection. This is described in the Fig. 8, Fig. 9 and Fig. 10 shown. As can be seen from these figures, the camera 7 can be used with the door 5 open to determine, on the one hand, whether the cutlery drawer 10, the upper basket 9 and / or the lower basket 8 have been removed from the wash container 2 for loading, and, if so, to determine the extent to which loading has taken place.

[0062] Camera 7 can also be used to detect a spray arm blockage. Fig. Figure 14 provides an example of such a spray arm blockage.

[0063] The spray arm blockage test is performed, for example, by using a previously created standard image of an unblocked situation as a reference image. During the speed detection process, a comparison with this reference image can then be made. If these images are not identical, a blockage is present, which can then be communicated to the user, for example, via display devices on the dishwasher itself or via a suitable wireless connection, even using a mobile device such as a smartphone. To increase test reliability, a spray arm blockage test using camera 7 can optionally be supplemented by a simultaneous check of the water diverter position and / or an additional time-based control query.

[0064] Camera 7 can be used not only to view the already existing information based on the Fig. Perform the load detection described in sections 5 to 9; zone-specific load states can also be detected, differentiated between upper and lower baskets, as shown schematically in Fig. 16 is shown.

[0065] As can be seen from the presentation according to Fig. As shown in Figure 16, both the upper and lower baskets are divided into four zones. The load status is graphically represented by the different shading of the zones shown. For example, the two zones of the lower basket containing the plates 12 are shown in black, corresponding to a 100% load. In comparison, the rear right loading zone of the upper basket is lighter, representing, for instance, a load of only 20%.

[0066] The load detection according to Fig. 16 can be carried out as a one-time verification step in parallel with the speed determination procedure, as can be seen from the illustration according to Fig. 15.

[0067] The images from process step 3 for determining the rotational speed are compared, according to process step a, with a previously created reference image of an empty dishwasher 1. A cross-sectional image is then created from the comparison images, according to process step b, with the cross-sectional image providing an initial estimate of the load status. Using the cross-sectional image, for example, a percentage load distribution can be generated with respect to the two levels formed by the upper and lower baskets.

[0068] According to process step c, a detailed load detection is performed, for which purpose the depicted wash chamber is divided into the previously described zones. A concrete zone comparison can then be carried out, thus allowing for a more detailed load status detection.

[0069] Depending on the comparison result, a corresponding measure can then be initiated according to procedure step d, for example a discontinuous control of the spray arm speed, which takes into account different loading conditions in individual zones.

[0070] According to process step e, the load detection is then completed and the rotational speed determination of the spray arms is continued in accordance with the above explanations.

[0071] A discontinuous control of the spray arm speed is used, for example, in Fig. 17 are shown. The diagram shows the following Fig. 17 in the upper part the circulation pump speed and in the lower part the water diverter position. As can be seen from the illustration according Fig. As of 17, the water diverter is initially in a first position, in which only the middle spray arm is operated. During this period, the speed of the circulation pump is also kept constant. The water diverter then switches to simultaneous operation of the upper and lower spray arms, while the middle spray arm is switched off. During this spray arm operation, the circulation pump runs at an increased speed and discontinuously, as shown in the graph of the circulation pump speed. Reference sign 1 dishwasher 2 washing containers 3 Interior (washing area) 4 Opening 5 door 6 Inside 7 Camera 8 Lower basket 9 Upper basket 10 cutlery drawer 11 items to be washed 12 plates 13 pots / pans 14 additional dishes / glasses 15 Spray device 16 Circulation pump 17 upper spray arm 18 medium spray arm 19 lower spray arm

Claims

[1] Method for determining the rotational speed of a spray arm (18) of a dishwasher (1), in which images are taken of the interior (3) of a washing container (2) of the dishwasher (1) housing the spray arm (18) by means of a camera (7), which are then processed for evaluation and subsequently compared with each other, and in which the rotational speed of the spray arm (18) is calculated as a function of the result of the image comparison. [2] Method according to claim 1, characterized by , that an image created by the camera (7) of the interior (3) is reduced to a section representing the spray arm area. [3] Method according to claim 1 or 2, characterized by , that an image is processed by changing the color, contrast, saturation and / or the like. [4] Method according to any one of the preceding claims, characterized bythat the images are created at a predetermined frequency, preferably below 25 Hz. [5] Method according to any one of the preceding claims, characterized by , that the number of pixels representing the light and dark areas of an image is summed up and this sum is transferred to a curve diagram. [6] Method according to claim 5, characterized by , that the spray arm speed is calculated based on the curve profile of the curve diagram. [7] Method according to any one of the preceding claims 1 to 3, characterized by , that continuous image generation, preferably with a frequency of at least 25 Hz, takes place with simultaneous interior lighting in a flashing light operation with a variable, predetermined frequency. [8] Method according to claim 7, characterized by, that consecutively created images are compared with each other, whereby in the case of identity the spray arm rotation speed is calculated based on the light flash frequency. [9] Method according to any one of the preceding claims, characterized by , that an image comparison is carried out with a reference image previously created and stored in the control unit of the dishwasher (1). [10] Method according to any one of the preceding claims, characterized by that load detection is carried out using image capture. [11] Method according to any one of the preceding claims, characterized by , that the rotational speed of another spray arm (17, 19) is determined acoustically.

Images