Patent Document

FIELD OF THE INVENTION 
       [0001]    The present invention relates to an industrial robot transmission system for the transmission of movement to a robot part, and an industrial robot comprising such a system. The invention also relates to a method for preventing the deterioration of a lubricant due to absorption of moisture, inside an industrial robot used in surroundings with high humidity, and further to a method for absorbing moisture inside a gearbox containing a lubricant in an industrial robot. 
       BACKGROUND OF THE INVENTION 
       [0002]    Outdoor applications are a relatively new field of use for industrial robots. During outdoor use of robots under humid conditions, it has been found that the lubricant used in e.g. the gearbox of the robot, after some time displays a moisture content that is higher than normal, due to the moisture from the surroundings penetrating into the gearbox. This is a disadvantage since it could lead to less good lubrication, increased wear on machine parts that need lubrication, a shorter life time and consequently higher costs. In order to avoid this, the lubricant has to be checked and changed at shorter intervals which also will increase costs. Alternatively, the lubricant that is used must be a lubricant that is capable of standing higher moisture in the surroundings without negative effects on its lubricating function and capabilities. Another conceivable alternative would be to make the gearbox much tighter, if possible. All of these alternatives involve increased costs. 
         [0003]    There is also a problem created by increased moisture content in the gearbox, when the moisture is not absorbed by the lubricant, but is present as free water, dissolved or emulsified by the lubricant, which is equally or more detrimental to the function of the lubricant. 
         [0004]    Industrial robots may also be used in other environments where the humidity is high, for example in foundry or wash-down environments such as in food industry. A similar problem with increased moisture content in lubricants may also occur in such applications. 
         [0005]    Problems with lubricants absorbing moisture also may occur due to temperature variations which result in a temperature difference between the surroundings and the interior of the gearbox, and this will in turn result in pressure difference between the surroundings and the interior of the gearbox, which may lead to an increase of moisture in the gearbox when humid air is sucked into the gearbox due to lower internal pressure. For example, this may be the case when a robot is operated in two or three shifts, and the day temperature may be considerably higher than the night temperature. These temperature variations in combination with a humid surrounding are a particularly challenging problem. 
       SUMMARY OF THE INVENTION 
       [0006]    One object of the present invention is to provide a solution to problems related to too high moisture contents in lubricants used in industrial robots, and thereby increase the possibility of using industrial robots in environments with high humidity. The object is also to make this possible in a simple and inexpensive way. 
         [0007]    These objects are achieved by the features defined in the present teachings. 
         [0008]    According to a first aspect of the present invention, is defined an industrial robot transmission system for the transmission of movement to robot parts, comprising at least one motor and at least one gearbox containing a lubricant, characterized in that the gearbox is provided with an integrated moisture absorbing device comprising a moisture absorbing material adapted to absorb moisture contained in the gearbox. By providing the gearbox with an integrated moisture absorbing device, the moisture in the gearbox will be absorbed by the moisture absorbing device instead of being absorbed, dissolved or emulsified by the lubricant, and the moisture absorbing device may also absorb water from the lubricant. This is defined in that the moisture absorbing device comprises a moisture absorbing material with higher affinity to water than the affinity of the lubricant to water. 
         [0009]    It is foreseen that the lubricant may come into contact with the moisture absorbing material, in which case the moisture absorbing material may absorb lubricant instead of water or moisture, and become saturated with lubricant, in which case it will not be able to absorb moisture. This may be prevented by the moisture absorbing device comprising a moisture absorbing material with higher affinity to water than to the lubricant. 
         [0010]    In many applications it will be desirable that the affinity to water of the moisture absorbing material is such that the absorbing material will both absorb moisture in a gaseous phase from within the gearbox and water present as free water, dissolved in, absorbed or emulsified by the lubricant, as well as preventing lubricant from being absorbed by the moisture absorbing material. 
         [0011]    Affinity should be interpreted to include both chemical affinity and physical affinity or a combination thereof. 
         [0012]    By integrating the device in the gearbox is provided a simple and inexpensive means for absorbing moisture and thereby prolonging the time span between lubricant changes, decreasing the risk of damage to parts in the gearbox due to reduced lubricating function of the lubricant which in turn is due to an excessive amount of moisture having been absorbed by the lubricant. 
         [0013]    By the expression integrating is intended a device that can be kept mounted in the gearbox all the time, and including during operation of the gearbox. There will be no need for any separate external devices that have to be connected and disconnected. 
         [0014]    According to one feature, the moisture absorbing device may be removable. Through this, the device may be exchanged whenever desirable, and replaced by a new device. 
         [0015]    The moisture absorbing device may be integrated in the gearbox by being provided as part of a plug located in a hole in a wall of the gearbox. The moisture absorbing device with its absorbing material may be arranged in several ways. For example, it may be provided mainly outside the gearbox and the moisture will be absorbed via a hole in the plug providing a communication from the interior of the gearbox to the moisture absorbing material of the device. In an alternative, the moisture absorbing device may be provided mainly inside the gearbox, being attached to the plug and in which case the moisture absorbing material inside the gearbox may be surrounded by a moisture permeable shell or film or similar, if necessary. According to another alternative, the moisture absorbing material may be contained in the plug. 
         [0016]    According to another embodiment, the gearbox is provided with at least one oilplug hole for the filling or and draining of lubricant in the gearbox, and the moisture absorbing device is integrated in an oilplug designed to be inserted in the oilplug hole. If a regular oilplug hole of the gearbox can be used for a plug with an integrated moisture absorbing device, this provides a very simple and economic solution, since no separate hole for the moisture absorbing device will be necessary. 
         [0017]    It will also be advantageous to have some provision in relation to the moisture absorbing device that will provide an indication of whether the device can still absorb moisture or if it has used up its moisture absorbing capacity, and needs to be replaced. To this end, the moisture absorbing device may comprise a moisture absorbing material having a physical property that is adapted to change depending on the amount of absorbed moisture. Examples of such physical properties may be colour, volume, electrical resistance etc. 
         [0018]    According to another alternative, the moisture absorbing device may comprise a sensor device adapted to emit a signal, reflecting the status of absorbed moisture in the moisture absorbing device, to an indicator device which indicates the status of absorbed moisture. 
         [0019]    As a further alternative, the moisture absorbing device may comprise a sensor device adapted to emit a signal, reflecting the status of absorbed moisture in the moisture absorbing device, to a control system. This control system may be a robot controller, a programmable logic controller (PLC), a remote service, a remote control device or any other type of control system or device regularly used in connection with industrial robots. 
         [0020]    According to another aspect of the invention is defined an industrial robot comprising a transmission system with an integrated moisture absorbing device having the above features. 
         [0021]    According to yet another aspect of the invention is defined a method for preventing the deterioration of a lubricant due to absorption of moisture, inside an industrial robot used in surroundings with high humidity, characterized by integrating a moisture absorbing device comprising a moisture absorbing material in a robot part containing the lubricant. By integrating a moisture absorbing device in a robot part containing a lubricant, the moisture will be absorbed by the moisture absorbing device instead of being absorbed by the lubricant, and moisture already absorbed by the lubricant may be reduced, as already discussed above. Consequently deterioration of the lubricant due to excessive moisture content is prevented, and the life span of the lubricant is prolonged. This may be achieved by choosing a moisture absorbing material with higher affinity to water than the affinity of the lubricant to water. 
         [0022]    It may also be prevented that the moisture absorbing material absorbs lubricant, as also explained above, by choosing a moisture absorbing material with higher affinity to water than to the lubricant. 
         [0023]    According to another feature, the method may be characterized by choosing a moisture absorbing material having a physical property that is adapted to change depending on the amount of absorbed moisture. Examples of such physical properties may be colour, volume, electrical resistance etc. 
         [0024]    According to a further feature, the method may be characterised by integrating the moisture absorbing device in a part of a plug located in a hole in a wall of a gearbox containing lubricant and being part of a transmission system for the transmission of movement to a robot part. 
         [0025]    According to another feature, the method may be defined by integrating the moisture absorbing device in an oilplug of the gearbox. The advantages related to this have been described above. 
         [0026]    Finally, and according to a further aspect of the present invention is defined a method for absorbing moisture inside a gearbox containing a lubricant in an industrial robot, characterized by integrating a moisture absorbing device comprising a moisture absorbing material in the gearbox. 
         [0027]    Other features and advantages of the invention may be apparent from the following detailed description of embodiments. 
         [0028]    It should be mentioned that the expression lubricant is intended to encompass any type of lubricant that may be used in an industrial robot and in particular in a gearbox, for example liquid or solid lubricants of any type. 
         [0029]    It should also be mentioned that by moisture is intended fluid moisture such as water in gaseous or liquid form, including such moisture which may be contained in other gases, liquids or solids. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    The invention will now be described in more detail, with reference being made to the enclosed schematic drawings illustrating different aspects and embodiments of the invention, given as examples only, and in which: 
           [0031]      FIG. 1  illustrates schematically an industrial robot; 
           [0032]      FIG. 2  shows parts of an industrial robot comprising a transmission system according to the present invention and including a moisture absorbing device; 
           [0033]      FIG. 3  shows a first embodiment of a moisture absorbing device according to the present invention; 
           [0034]      FIG. 4  shows a second embodiment of a moisture absorbing device according to the present invention; 
           [0035]      FIG. 5  shows a third embodiment of a moisture absorbing device according to the present invention; and 
           [0036]      FIG. 6  shows a fourth embodiment of a moisture absorbing device according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    In the drawings, the same elements or corresponding elements in the different embodiments have been given the same reference number. 
         [0038]    In  FIG. 1  is schematically illustrated an industrial robot. An industrial robot  1  comprises a control system, a manipulator, and electric motor units configured to attend to the movements of the manipulator. Each motor unit comprises an electric motor, a brake, a gearbox and other gearing as necessary in order to form a transmission system for the transmission of movement to a movable part of the robot. 
         [0039]    The illustrated robot is a conventional six-axis industrial robot  1 . However, it is apparent that the invention is not limited to such a robot, but may be used also in robots with more or less axes, and for other types of kinematic solutions such as parallel kinematic robots or SCARA robots. 
         [0040]    The illustrated robot has a stand  3  that is rotatably mounted on a base  2 , about a first axis of rotation A. In the stand  3 , a first robot arm  4  is rotatably journalled for rotation about a second axis of rotation B. The industrial robot further comprises a second robot arm  5 , which is rotatably journalled in the outer end of the first robot arm, for rotation about a third axis of rotation C. The second robot arm is also rotatable about a fourth axis of rotation D which coincides with the longitudinal axis of the second robot arm  5 . A wrist unit  6  is arranged at the outer end of the second robot arm  5 , and said wrist unit comprises a tilt part  7  which is rotatably journalled in the wrist unit  6  for rotation about a fifth axis of rotation E. A turn disc  8 , on which an end effector or tool may be mounted, is arranged on the tilt part for rotation about a sixth axis of rotation F. The manipulator is connected to a control system  1 a. 
         [0041]    In order to drive the connected parts in rotation about the respective axes A, B, C, D, E, F, a transmission system  9  is provided for each movable robot part, of which some of the motors  10  can be seen in  FIG. 1 . 
         [0042]      FIG. 2  illustrates parts of an industrial robot provided with a transmission system  9  according to the present invention. The robot parts are a base  2  and a stand  3 , and in the stand is arranged a gearbox  12  connected to an electric motor  10 . The transmission system comprising the electric motor  10  and the gearbox  12  transmits a rotational movement to a first robot arm  4  about the axis of rotation B, as seen in  FIG. 1 . The gearbox is filled with a lubricant, in most cases oil. 
         [0043]    A gearbox  12  is in most cases provided with three holes in the gearbox wall  13  in which so called oilplugs are inserted. There is one oilplug and hole for inspection, there is one oilplug and hole for filling oil or other lubricant into the gearbox, and there is one oilplug and hole for draining oil from the gearbox. These holes may be used for the installation of a moisture absorbing device according to the present invention. Alternatively, a separate hole may be made in the wall of the gearbox for the installation of a moisture absorbing device according to the present invention. All of these possible holes that may be used for a moisture absorbing device have been given the reference number  14 , irrespective of if they are already existing holes or separate holes made for this particular purpose. However, in most cases it is preferable that the hole is located underneath the normal surface of the lubricant. 
         [0044]    In the following examples of embodiments illustrated in  FIGS. 3-6 , the interior of the gearbox is designated by  15  and the wall of the gearbox is designated by  14 . 
         [0045]    A first embodiment of a moisture absorbing device  20  is shown in  FIG. 3 . A hole  14  is provided in the gearbox wall  13 , and in this hole a plug  22  is inserted, thereby plugging the hole. The plug is designed with a part comprising a moisture absorbing device  20 , which is thus integrated in the gearbox. The part of the plug comprising the moisture absorbing device is located externally of the gearbox. The moisture absorbing device comprises a hollow part  24  in the interior of the plug, which hollow part is located externally of the gearbox when the plug is inserted in the hole  14 . In this hollow part  24  there is arranged a moisture absorbing body  26  of a moisture absorbing material  27 . Since also the part of the plug that extends through the hole  14  is hollow, there is free communication between the interior  15  of the gearbox and the interior of the plug with the moisture absorbing material  27 , and the moisture absorbing material can consequently absorb moisture contained inside the gearbox. 
         [0046]    The moisture absorbing material can absorb moisture from the air in the gearbox, or even liquid moisture (water), and it can absorb moisture contained in the oil in the gearbox. This is made possible by choosing a moisture absorbing material that has a higher affinity to water than the affinity of the oil to water, thus preventing that the oil absorbs the moisture/water. The moisture absorbing material may also be chosen to have a higher affinity to water than to the oil, in order to prevent that the moisture absorbing material absorbs oil instead of moisture/water. It is intended to encompass both materials with chemical affinity and materials with physical affinity. Examples of suitable materials are absorbing polymers, e.g. so called super absorbent polymers such as starch-acrylonitrile copolymers, cross-linked acrylic homo-polymers, cross-linked polyacrylate/polyacrylamide copolymers; molecular sieves such as silica gel, zeolites—microporous aluminosilicates; minerals such as calcium sulphate, calcium chloride, magnesium sulphate; clays such as montmorillonite clay. The moisture absorbing material may also be chemically compatible with the used lubricant, i.e. the lubricant may not be chemically affected by the moisture absorbing material, e.g. due to chemical reactions with the material or catalysed by the material. 
         [0047]    Materials with a combined chemical and physical affinity may also be used, e.g. materials having physical affinity in the form of hollows, and where the hollows also have a chemical affinity, in line with the above discussion regarding affinity. Examples of such materials are zeolites, e.g. molecular sieve  3 A, sodium/potassium aluminosilicate. 
         [0048]    In  FIG. 4  is shown a second embodiment of a moisture absorbing device  30 . This device resembles the device according to the first embodiment in that it comprises a hollow part  34  in the interior of the plug  32 , which hollow part is located externally of the gearbox when the plug is inserted in the hole  14 . In this hollow part  24  there is arranged a moisture absorbing body  36  of a moisture absorbing material  37 . There is free communication between the interior  15  of the gearbox and the interior of the plug with the moisture absorbing material  37 . In this embodiment the moisture absorbing body  36  is illustrated as smaller than in the first embodiment, and there is a certain amount of free space between the body  36  and the inner wall of the hollow part  34 . This allows for the moisture absorbing material  37  to expand/change volume inside the hollow part  34 , during absorption of moisture. The moisture absorbing material may be any one suitable chosen from the above mentioned examples of materials, or any other suitable expanding material. The expansion of the material may be used as an indicator of how much moisture the device has absorbed. If required, and depending on the material used, the moisture absorbing material may be contained within a moisture/water permeable film or shell  38 , or similar as illustrated in  FIG. 4 . This will prevent that the material spreads into the interior of the gearbox. This shell should be of an expandable or elastic material in order to accommodate an expansion of the volume of the moisture absorbing material. It should also be compatible with the used lubricant, in the same way as the moisture absorbing material as described above. 
         [0049]    Examples of possible moisture/water permeable shell materials are polyethylene film, polyester, laminates, etc. 
         [0050]    In  FIG. 5  is illustrated a third embodiment of a moisture absorbing device according to the present invention. In this embodiment, the part of the plug  42  that forms the moisture absorbing device  40  is located in the interior  15  of the gearbox. As in the previous embodiments, the device comprises a moisture absorbing body  46  comprising a moisture absorbing material  47 . The moisture absorbing material  47  is contained in a water permeable film or shell  48 , which keeps the moisture absorbing material in place and attached to the plug  42 , while at the same time it does not prevent the material from absorbing moisture. The function corresponds to what has been described above and examples of materials are the same as given above. 
         [0051]    In  FIG. 6  is illustrated a fourth embodiment of a moisture absorbing device  50  according to the present invention. This device is integrated in an oilplug  52 , which may be e.g. an inspection oilplug inserted in an inspection hole in the gearbox. The moisture absorbing body  56  with its moisture absorbing material  58  is completely contained within the plug, by means of being placed in a hollow portion  54  provided within the plug, with an opening facing the interior  15  of the gearbox. This plug is primarily designed to be utilizable as a regular oilplug. 
         [0052]    It may be desirable to be able to obtain information about the status of the moisture absorbing material in an easily accessible manner. It has already been described in connection with  FIG. 4  how the moisture absorbing material can be of a kind that changes volume depending on the degree of moisture absorption. Alternatively, the absorbing material may be chosen to have other physical properties that are adapted to change depending on the amount of absorbed moisture. Another example is a moisture absorbing material of a kind that changes colour depending on the amount of absorbed moisture. This change of volume or colour can for example be visually checked in order to determine if the device has absorbed so much moisture that it is now time to replace it with a new device. The visual check can be made by removing the plug with the moisture absorbing device. In  FIG. 1  is illustrated another alternative. The external wall of the hollow part  24  of the plug  22  is provided with a transparent portion  21  through which the absorbing material  27  can be visually inspected. Another example of a possible changing physical property is electrical resistance. 
         [0053]    According to another alternative, illustrated in  FIG. 5 , the moisture absorbing device may comprise a sensor device  45  adapted to emit a signal, reflecting the status of absorbed moisture in the moisture absorbing device, to an indicator device which indicates the status of absorbed moisture. The indicator device may for example be a lamp or a device giving a sound signal. Alternatively, the sensor device may emit a signal to a control system  1 a. This control system may be a robot controller, a remote service, a remote control device or any other type of control system or device regularly used in connection with industrial robots. The signal may be emitted via any suitable means, wireless or not. Examples of possible sensors are sensors using electrical resistance to measure moisture level. 
         [0054]    Naturally, the different types of status indicators, volume change, colour change, sensors emitting signals to different systems, may be applied in any one of the described embodiments of the moisture absorbing device. 
         [0055]    In all of the illustrated embodiments, the plug with the moisture absorbing device may be removable in order to be able to replace the moisture absorbing device/plug with a new one, whenever desired or necessary. 
         [0056]    The present invention is not limited to the disclosed examples, but may be modified in many ways that would be apparent to the skilled person, within the scope of the appended claims.

Technology Category: y