Patent Description:
Equipment used in the food processing of protein industry (that is meat, poultry, fish, seafood and dairy) is subject to strict hygiene requirements and must be washed down daily using hot high pressure water and chemical agents. A robot intended for food processing in wash down applications should have a complete stainless-steel frame which is hygienically designed to be easy to clean. The robot needs to have a high water protection rating - Ingress Protection <NUM> (IP69K). The IP69K rating defines what is needed to provide protection against ingress of dust and high temperature, high pressure water - making products with this certification suitable for use in conditions where equipment must be carefully sanitized. In industries such as food processing, where hygiene and cleanliness is paramount, equipment must be able to withstand rigorous high pressure, high temperature wash-down procedures. In many industries, where dust and dirt can be an issue, it is important to ensure that dust and dirt cannot penetrate the casing of a product and cause it to fail.

Even if the robot is provided with a stainless-steel frame, the joints may be a source to contamination. Therefore, the joints of a robot should be sealed such that no fluid or material can enter the joints during working or wash down, and also avoid that fluid such as grease can come out of the joints and potentially contaminate the food that is being processed. For example, from <CIT> it is known to have a sealing device for a joint section of a robot. The sealing device comprises overlapped seal portions having a multi-stage configuration.

The state of the art further includes <CIT>, which discloses a manipulator, such as a multiaxial industrial robot, particularly for use in contamination-endangered environments, including a plurality of scavenging areas to which a scavenging medium can be supplied and located in the vicinity of the drive unit of the manipulator. A plurality of groups of drive units has in each case its own scavenging area associated with it.

<CIT> discloses a work chamber, which has an opening for insertion of a robot manipulator arm provided by a sleeve fitted through the work chamber wall, provided with a hollow flexible sealing element, which is supplied with a pressurized gas via an inflation valve, for providing an automatic seal around the outside of the manipulator arm, by cooperation with the inside surface of the sleeve.

<CIT> discloses the following process: After a gas or liquid filled inflatable seal has been exhausted to atmosphere by opening valves it is partially evacuated, evacuation being performed by closing the first valve and opening a second valve, the latter causing exhaustion of a chamber which allows a spring to displace a piston or flexible diaphragm and thus suck fluid from the seal into the opposed chamber. The chamber is filled with pressurized fluid during inflation of the seal. To inflate the seal, third and fourth valves are opened and the first and second valves are closed. This allows fluid from a source to enter the seal and also the chamber whereby to displace the piston or diaphragm against the force of the spring.

<CIT> discloses a robot joint sealing structure is provided with: a fitted end, which is provided on an end of a second member and is fitted in the cylindrical end of a first member; a circumferential groove formed so as to extend over the entire circumference of the inner surface of the cylindrical end; and a circular sealing member that is accommodated inside the circumferential groove and adheres closely to the outer circumferential surface of the fitted end. The fitted end is formed to have a smaller diameter than the main body of the second member. The surface spanning the level difference between the main body and the fitted end faces the end face of the cylindrical end in close proximity in the axial direction. Between the level difference surface and the end face of the cylindrical end, a gap, which extends over the entire circumference, is open to the outside of the first member and the second member, and widens towards the outer circumference, is formed.

<CIT> discloses a robot joint with a first part and a second part, which are arranged to have a relative movement in-between, and with a joint gap that separates the first and second part from each other. The robot joint further comprises a sealing structure formed by a pressurized chamber and by inner and outer gaskets. The sealing structure is designed to maintain a small outward air flow that keeps lubricant, dust and foreign matter away from an inside portion of the robot.

<CIT> discloses a bottle-filling appliance with a rotating shaft that is retained in a housing by a bearing. Multiple inflatable seals (e.g., expandable tubes) are contained in hollow annular spaces that are distributed over the axial direction of the shaft. When the tubes are inflated with pressurized fluid, they will exert a sealing radial pre-tensioning force between the housing and the shaft.

<CIT> discloses a shaft sealing device, in which an elastic and pressurizable ring is installed between a hermetically sealed container and the shaft sealing device at a shaft sealing portion of a rotary shaft penetrating the hermetically sealed container.

Since the joint seal bridges two robot arms, the seal will be subjected to sustained dynamic loads as long as the robot operates. Eventually the seal will be worn extensively and could no longer protect against contamination/water ingression. In most cases, the wear happens at the contact surface due to shear load. The shear load is proportional to the axial load applied on the seal, or, in other words, the clamping force.

It is an object of the disclosure to alleviate at least some of the drawbacks with the prior art. It is an object to provide a robot joint sealing solution that provides a fluid tight sealing of the joint with a minimum wear-down of the same. This object and others are at least partly achieved by the invention according to the independent claims, and by the embodiments according to the dependent claims.

The disclosure relates to a system according to claim <NUM>, comprising a robot with a robot joint comprising a first part and a second part arranged to have a relative movement in between, and a joint gap spacing the first part and the second part from each other. The robot joint comprises an inflatable seal accommodated in the joint gap to provide a fluid- tight sealing of the joint. This solution provides a flexible sealing, especially for hygienic robot joints, as the seal is inflatable. The robot joint with the inflatable seal solves the conflicting requirements for a single joint seal, to both provide a fluid tight sealing and to enable relative movement of the first part and second part of the joint. The solution enables the robot joint to work in different modes with equivalent efficiency. The result may be better sealing performance and long life time of the seal, with an implied cost reduction due to the long life time of the seal. The design is rather simple and compact, and the cost for implementing and using the seal is thus low. The design is also hygienic due to less risk and/or less amount of worn particle emission.

According to some embodiments, the joint gap is annular. According to some embodiments, the inflatable seal is annular. Thus, the inflatable seal may match the shape of the joint gap, such that may be used for efficient sealing of an annular joint gap.

According to some embodiments, the first part and/or the second part has a structure designed to force the inflatable seal to expand in a direction towards the second part when inflating the inflatable seal. Thereby, the inflatable seal can be controlled in a predetermined manner to seal the joint gap according to different needs.

According to some embodiments, the first part comprises a first axially extending structure delimiting the inflatable seal against the exterior of the robot joint, and a second axially extending structure, the first axially extending structure and the second axially extending structure delimiting a space where the inflatable seal is accommodated, and wherein the first axially extending structure and the second axially extending structure are designed to force the inflatable seal to expand in a direction towards the second part when inflating the inflatable seal. Thus, the first structure and the second structure guide the inflatable seal to expand in a certain direction.

According to some embodiments, the structure is designed to prevent radial expansion of the inflatable seal. Thereby, the expansion of the inflatable seal can be controlled to expand in a desired axial direction.

According to some embodiments, the inflatable seal is attached to the first part. Thereby, the inflatable seal will not change its position with respect to the first part, for example become twisted, and thereby compromise the sealing function.

The system according to the invention further comprises a control unit, a valve arrangement and a tube arrangement fluidly connected to a source of pressurized fluid and to the inflatable seal. The control unit is programmed to pressurize the inflatable seal by means of the valve arrangement and the tube arrangement such that the inflatable seal expands in an axial direction towards the second part to seal the joint gap between the first part and the second part. Thus, the sealing function of the inflatable seal can be controlled to efficiently seal the joint.

The control unit is configured to control the valve arrangement to pressurize the inflatable seal in synchronization with the robot operation. Thus, the sealing function of the inflatable seal can be controlled to efficiently seal the joint adapted to the operation of the robot such that the seal is spared from wear.

The control unit is configured to control the valve arrangement to pressurize the inflatable seal in synchronization with the robot operation, such that the inflatable seal is pressurized to a predetermined low pressure when the robot is working, and to a predetermined high pressure when the robot is exposed to high pressure wash down and/or is shut down, wherein the predetermined high pressure is higher that the predetermined low pressure. Thereby, the wear of the inflatable seal may be lowered, as the inflatable seal is pressed against the sealing surface of the second part with a lower clamping force when joint parts are moving, than when the joint parts are not moving, such that the friction between the sealing surface and the inflatable seal becomes less and thereby decreases wear. During wash-down, the robot is normally not powered or at least not operating, but the joints have to withstand high pressure. By inflating the inflatable seals to a high pressure during wash-down, the inflated inflatable seals provide an efficient sealing during the wash-down.

According to some embodiments, the robot comprises a plurality of robot joints as previously described, where the inflatable seals are fluidly connected in series by means of the tube arrangement. Thereby, a plurality of robot joints may be sealed efficiently at the same time.

According to a fourth aspect, the disclosure relates to a method for sealing a joint gap of a robot joint. The robot joint comprises a first part and a second part with a relative movement in between, and the joint gap spaces the first part and the second part from each other. The robot joint comprises an inflatable seal accommodated in the joint gap to provide a fluid-tight sealing of the joint. The method comprises pressurizing the inflatable seal such that the inflatable seal expands in an axial direction towards the second part to seal the joint gap between the first part and the second part. Thus, the sealing function of the inflatable seal can be controlled to efficiently seal the joint.

According to some embodiments, the method comprises pressurizing the inflatable seal in synchronization with the robot operation. Thus, the sealing function of the inflatable seal can be controlled to efficiently seal the joint adapted to the operation of the robot such that the seal is spared from wear.

According to the invention, the method comprises pressurizing the inflatable seal to a predetermined low pressure, upon receiving an indication that the robot is working; and pressurizing the inflatable seal to a predetermined high pressure upon receiving an indication that the robot is not working and/or is exposed to wash down, wherein the predetermined high pressure is higher that the predetermined low pressure. Thereby the wear of the inflatable seal may be lowered, while still providing an efficient sealing.

According to a fifth aspect, the disclosure relates to a computer program, wherein the computer program comprises a computer program code to cause a control unit, or a computer connected to the control unit, to perform the method as described herein.

According to a sixth aspect, the disclosure relates to a computer program product comprising a computer program code stored on a computer-readable medium to perform the method as described herein, when the computer program code is executed by a control unit or by a computer connected to said control unit.

In the following a robot joint will be described that has a fluid-tight sealing of the joint, and also a robot comprising at least one such robot joint, a system comprising the robot and a method for sealing such a robot joint.

The herein described robot joint is provided with a seal that is inflatable. The inflatable seal is provided in a joint gap spacing a first part and a second part of the robot joint, with a relative movement in between. With such a robot joint, it is possible to meet conflicting requirements found for a single joint seal, thus to both seal the joint and allow the parts of the joint to move in relation to each other, because the inflatable seal can be made to work in different modes. In a first mode, the inflatable seal provides operational protection. For example, when the robot operates in a meat processing factory, the inflatable seal shall protect against external contamination, such as incoming blood splashes. In this case, the contact pressure between the inflatable seal and a sealing face of the second part shall be set just at minimum level, so as to minimize the wear of the inflatable seal, while still providing a sealing function of the joint gap. In the second mode, the inflatable seal provides wash-down protection. During that phase, the joint seal shall protect against high pressure/temperature water jet. Since the robot is kept stationary during wash-down, that is, no part is moving, there is no concern regarding the shear load (friction force) on the inflatable seal. In this case, ideally, the contact pressure between the inflatable seal and the sealing face of the second part shall be set as high as possible, so as to maximize sealing capability. Thus, by minimizing the axial load of the inflatable seal of the joint during robot operation, the seal life time may be prolonged. Obviously, a fixed-profile seal could hardly fulfil the requirements for different operating modes, while by introducing an inflatable seal, the sealing becomes flexible.

<FIG> illustrate an industrial robot <NUM> with six (<NUM>) axes <NUM>-<NUM>, hereafter referred to as "robot <NUM>". The robot <NUM> is a programmable robot that has six degrees of freedom (DOF). Each axis comprises a driving mechanism (not shown) for driving an arm or a wrist. The driving mechanism comprises a driving motor, for example a brushless DC motor. A transmission comprising speed reducers and/or gearboxes transmits the torque from the driving motor, via an output shaft of the driving motor, to the joint <NUM> of the axis. The joint <NUM> comprises a first part <NUM> and second part <NUM> (<FIG>). The first part <NUM> is typically arranged stationary in relation to the driving motor of the axis, and the second part <NUM> is arranged in relation to the outgoing shaft of the driving motor, and rotates in accordance with the rotation of the arm or wrist of the axis. Thus, the second part <NUM> will then rotate in relation to the first part <NUM> when the joint is operated. The first part <NUM> and the second part <NUM> are thus rotatable in relation to each other. Between the first part <NUM> and second part <NUM> there is a joint gap <NUM> (<FIG>), and an inflatable seal <NUM> is arranged to seal the joint gap <NUM>. Thus, the inflatable seal <NUM> is arranged to seal the first part <NUM> and the second part <NUM>. In the robot <NUM> of 1A and 1B, each joint is sealed with an inflatable seal. That is, the joint gap of the joint 20a of the first axis <NUM> is sealed with a first inflatable seal 10a, the joint gap of the joint 20b of the second axis <NUM> is sealed with a second inflatable seal 10b, the joint gap of the joint 20c of the third axis <NUM> is sealed with a third inflatable seal 10c, the joint gap of the joint 20d of the fourth axis <NUM> is sealed with a fourth inflatable seal 10d, the joint gap of the joint 20e of the fifth axis <NUM> is sealed with a fifth inflatable seal 10e and the joint gap of the joint 20f of the sixth axis <NUM> is sealed with a sixth inflatable seal 10f. It should be understood that a robot may comprise more or less joints than six, and thus more or less inflatable seals than six. It should also be understood that the number of inflatable seals may be less than the number of joints i.e. not every joint needs to comprise an inflatable seal.

<FIG> illustrate inflatable seals <NUM> according to two different embodiments of the invention, that can be used as the inflatable seals 10a-10f in <FIG>, in isolation. The inflatable seal <NUM> may be produced from elastomers with high modulus of elasticity and considerable elongation. For example, the inflatable seal <NUM> can be made of silicone, styrene butadiene rubber or ethylene propylene. The material may be provided with an agent preventing bacterial and microbial growth, to meet the needs of hygienic applications. The inflatable seal <NUM> may be produced by joining together extruded or moulded sections. The inflatable seal <NUM> can thus be made into one, single, integrated piece.

The inflatable seal <NUM> is hollow and can be inflated by providing pressurized fluid to the interior of the inflatable seal <NUM> via an inlet 11a. The fluid of the inflatable seal <NUM> may be expelled via an outlet 11b. Such an embodiment is illustrated in <FIG>. The inlet 11a and the outlet 11b comprise small tubes that are rigidly attached, or integrated in, to the inflatable seal <NUM>, and fluidly communicate with the interior of the inflatable seal <NUM>. Alternatively, a common inlet/outlet 11c is provided via the same tube, as illustrated in <FIG>. The inflatable seal <NUM> has a circular shape, for example the shape of a hollow torus. In one embodiment, the inflatable seal <NUM> has the shape of an inflatable tube, for example similar to an inner tube of a bike wheel.

<FIG> illustrates a robot joint <NUM>, for example one of the robot joints 20a-20f of <FIG>, from the exterior of the joint <NUM>. As mentioned, the robot joint <NUM> comprises a first part <NUM> and a second part <NUM> arranged to have a relative movement in between. Thus, the first part <NUM> and the second part <NUM> are movably arranged in relation to each other, and thereby allow a relative movement between them. The output shaft <NUM> of the axis comprising the joint <NUM> is schematically illustrated in the figure with the dotted lines. The output shaft <NUM> thus connects the first part <NUM> and the second part <NUM> of the joint. The robot joint also comprises a joint gap <NUM> (<FIG>) spacing the first part <NUM> and the second part <NUM> from each other. The robot joint <NUM> comprises an inflatable seal <NUM> accommodated in the joint gap <NUM>, to provide a fluid-tight sealing of the joint <NUM>. In <FIG>, the inflatable seal <NUM> is illustrated in cross-section.

<FIG> illustrates an enlarged detail of <FIG>, namely a cross-section of the inflatable seal <NUM>. The first part <NUM> comprises a groove delimiting the inflatable seal <NUM> from three sides such as to force the inflatable seal <NUM> to expand in a direction towards the second part <NUM> when inflating the inflatable seal <NUM>, and thereby closing the joint gap <NUM>. In more detail, the first part <NUM> may comprise a first axially extending structure 22a, or wall part, delimiting the inflatable seal <NUM> against the exterior of the robot joint <NUM>. The first part <NUM> may also comprise a second axially extending structure 22b, or wall part, that delimits the inflatable seal <NUM> against the interior of the robot joint <NUM>.

In one embodiment, to make sure the inflatable seal <NUM> does not change its position in the housing, the inflatable seal <NUM> is assembled or attached to the first part <NUM>, for example by mechanical retaining and/or by gluing.

The inflatable seal <NUM> is arranged to receive pneumatic supply through the inlet 11a (<FIG>), to change its profile. The contact pressure between the inflatable seal <NUM> and the inner face 24a of the second part <NUM> can be adjusted by adjusting the inner pressure of the inflatable seal <NUM>, to adapt to different operating modes of the joint. During a wash-down, it may require a contact pressure as high as possible to secure the sealing capability against water jet, while during a regular operation mode, a lower contact pressure is needed to seal off casual external contaminations. The inner pressure for providing a low contact pressure, thus a contact pressure required to seal off external ingressions, may be set to an atmospheric pressure. This mode is also referred to as the first mode, and the inner pressure is referred to as a predetermined low pressure. The inner pressure for providing a high contact pressure should be high enough to withstand impact force from the wash down. This mode is also referred to as the second mode, and the inner pressure is referred to as a predetermined high pressure. It should be emphasized that during any mode, the inflatable seal <NUM> is securely sealing the robot joint. The contact pressure is the pressure of the inflatable seal <NUM> against the inner face 24c, or sealing face, of the second part <NUM>.

As illustrated in <FIG>, the first part <NUM> comprises a channel <NUM>, in which a first tube 27a is provided and attached to the inlet 11a for inflating the inflatable seal <NUM>, and a second tube 27b is provided and attached to the outlet tube 11b for deflating the inflatable seal <NUM>. This embodiment corresponds to the inflatable seal <NUM> illustrated in <FIG>, and the seals 10a-10f in <FIG>. Instead, the channel <NUM> may comprise only one tube <NUM> attached to a common inlet/outlet 11c of the seal <NUM>, corresponding to the inflatable seal <NUM> illustrated in <FIG> and the seals 10a-10f in <FIG>.

It is to be expected that dirt and/or bacteria will contaminate not only the part of the joint gap <NUM> delimited by the first part <NUM>, the second part <NUM> and the inflatable seal <NUM> and being open towards the exterior of the robot joint <NUM>, but also small distances within the interfaces between the inflatable seal <NUM> and the first part <NUM> and/or the second part <NUM>. That is, dirt and/or bacteria is expected to intrude between the inflatable seal <NUM> and the first part <NUM> and/or the second part <NUM>. It is furthermore expected that the interfaces between the inflatable seal <NUM> and the first part <NUM> and/or the second part <NUM> are particularly challenging to be properly cleaned during a wash-down. If the inflatable seal <NUM> consists of a homogenous material, inflating the same causes the inflatable seal <NUM> to be pressed even stronger against the first part <NUM> and the second part <NUM> at the region towards the exterior of the robot joint <NUM>, and thereby further counteracts the cleaning of the respective interfaces.

Referring to <FIG>, in order to mitigate the aforementioned issue, according to one embodiment of the inflatable seal <NUM> the same is designed to strongly change its shape at the region open towards the exterior of the robot joint <NUM>. In order to achieve this, the outer portion of the inflatable seal <NUM> in radial direction is provided with an enforcement <NUM> in the form of a profile or profiles made of spring steel. The enforcement <NUM> is stiff in relation to the surrounding relatively flexible material, and thereby it provides the inflatable seal <NUM> with a non-homogenous structure. The relatively flexible material in effect functions as a spring <NUM> allowing the interior of the inflatable seal <NUM> to expand towards the surrounding walls, but at the same time counteracting the force exerted by the pressurized air, as schematically illustrated in <FIG>. The enforcement <NUM> has a larger area exposed to pressurized air on the side of the first part <NUM> compared to that on the side of the second part <NUM>, which causes the enforcement <NUM> to move towards the first part <NUM> at inflation of the inflatable seal <NUM>. As the remainder of the inflatable seal <NUM> consists of relatively flexible material, this movement in its turn causes the inflatable seal <NUM> to strongly change its shape at the region open towards the exterior of the robot joint <NUM> such as to effectively expose the respective interfaces for cleaning.

In the following processes of pressurizing the one or several inflatable seals <NUM> of the robot <NUM> will be described.

<FIG> illustrate a system <NUM> comprising a robot <NUM> as described above, with a plurality of axes and joints, and inflatable seals 10a-10f sealing the joint gaps of the joints. <FIG> illustrates the whole system <NUM>, whereas <FIG> illustrates the robot <NUM> in another view to show axis <NUM> and <NUM> that are not visible in <FIG>, but for simplicity without all parts of the system <NUM>. The system <NUM> also comprises a control unit <NUM>, a valve arrangement <NUM> and a tube arrangement <NUM> fluidly connected to the source <NUM> of pressurized fluid and to the inflatable seals 10a-10f. For working applications, the robot <NUM> may be in need of pressurized fluid, and normally the robot <NUM> is already located in connection to a source <NUM> of pressurized fluid. In <FIG>, this source <NUM> of pressurized fluid is depicted as a box, but it should be understood that the source may include a container with pressurized fluid, a compressor for pressurizing the fluid etc..

In <FIG>, the plurality of inflatable seals 10a-10f are fluidly connected in parallel as also is illustrated in <FIG>. The same fluid tube <NUM> in the robot <NUM> is then used for deflation and inflation of the inflatable seals 10a-10f, and the fluid tube <NUM> is being passed through hollow spaces of the robot <NUM>, for example through hollow shafts <NUM>, <NUM>, <NUM> and <NUM> and inside an enclosure 100a of the robot <NUM>, to fluidly connect to all seals 10a-10f. In one embodiment, and in operation, the pressurized fluid is guided in the system <NUM> from a source <NUM> via a fluid line <NUM> inside the robot <NUM> to the furthest away located inflatable seal 10f, that is here sealing axis six. The valve arrangement comprises a three-position valve <NUM> and a first valve <NUM>. The tube arrangement <NUM> comprises a first fluid line <NUM>, a second fluid line <NUM>, a third fluid line <NUM> and a fourth fluid line <NUM>. The first fluid line <NUM> is connected between the source <NUM> and the three-position valve <NUM>. The second fluid line <NUM> is connected between the three-position valve <NUM> and the fluid tube <NUM>. The third fluid line <NUM> is connected between the three-position valve <NUM> and an outlet <NUM>. The fluid may be passed out from the system <NUM> to the outlet <NUM> for recycling the pressurized fluid, here schematically illustrated as a box. The fourth fluid line <NUM> connects the second fluid line <NUM> to the atmosphere. The fourth fluid line <NUM> is fitted with the first valve <NUM> and a manometer <NUM>. The default position of the valve <NUM> is to keep all flow terminals of the valve closed, which here is the middle position of the valve <NUM>, also referred to as a closed state. Before operating the robot <NUM>, a valve coil 67b is first energized, which ensures that all joint seals 10a-10f are deflated, so all joint seals 10a-10f keep minimum required contact force against contact surfaces. This corresponds to the right-hand side position of the valve <NUM>, whereby the air in the joint seals 10a-10f is passed to the outlet <NUM> for recycling the pressurized fluid, whereby the pressure in the joint seals 10a-10f will correspond to atmospheric pressure. Before wash down of the robot <NUM>, valve coil 67a is first energized and hold in its energized position, which allows pressurized gas to be passed into the joint seals 10a-10f to inflate the same. When the pressure inside the second fluid line <NUM> and thus also the fourth fluid line <NUM> reaches a desired pressure value, the manometer <NUM> will indicate this to the control unit <NUM>, which triggers a signal to be sent that de-energizes the valve coil 67a, whereby the valve <NUM> returns to its default position and keeps the pressure in the joint seals 10a-10f stable. A minimum threshold and/or maximum threshold can be set in the control unit <NUM>, such that in case of pressure change, the air pressure in the joint seals 10a-10f can be regulated back to the desired value. The valve arrangement <NUM> and the tube arrangement <NUM> may comprise a filter <NUM> and an orifice <NUM> arranged to the third fluid line <NUM>.

The valves herein are for example hydraulically, pneumatically or electrically controlled valves, that comprises springs and operators to change the state of the valves and thus the direction of the flow.

The control unit <NUM> is schematically illustrated in the <FIG> with a box, and it is understood that the control unit <NUM> is connected by wire or wirelessly to the valve <NUM> and to first valve <NUM>, and in some embodiments to the manometer <NUM>. The control unit <NUM> is programmed to pressurize the inflatable seals 10a-10f by means of the valve arrangement <NUM> and the tube arrangement <NUM>. By pressurizing the seals 10a-10f, the inflatable seals 10a-10f can be made to expand in an axial direction towards the second part <NUM> of each robot joint, to seal the joint gap between the first part <NUM> and the second part <NUM> of each robot joint with a high contact pressure. The control unit <NUM> is also programmed to de-pressurize the inflatable seals 10a-10f by means of the valve arrangement <NUM> and the tube arrangement <NUM> such that the inflatable seals 10a-10f contract in an axial direction towards the first part <NUM> of each robot joint, to lower the contact pressure from the inflatable seal on each robot joint.

The control unit <NUM> is configured to control the valve arrangement <NUM> to pressurize the inflatable seals 10a-10f in synchronization with the robot operation. For example, the control unit <NUM> is arranged to provide power to the valve arrangement <NUM> in synchronization with the robot operation, thus, when the robot <NUM> is operating, the valve arrangement <NUM> is also powered, and when the robot <NUM> is not operating or is not powered, the valve arrangement <NUM> is also not powered. In one embodiment, the control unit <NUM> is configured to control the valve arrangement <NUM> to pressurize the inflatable seals 10a-10f, such that the inflatable seals 10a-10f are pressurized to a predetermined low pressure when the robot <NUM> is working, and to a predetermined high pressure when the robot <NUM> is exposed to high pressure wash down and/or is shut down. The control unit <NUM> may for that purpose monitor the operation of the robot <NUM> to understand when the robot is exposed to wash-down, is operating or not operating etc. The control unit <NUM> may for example receive one or several signals from the robot <NUM> indicating the status of the same, that is, if the robot <NUM> is exposed to wash-down, whether it is operating or not, and whether it is powered. This functionality may alternatively be incorporated with the powering to the robot <NUM>, and thus, when the robot <NUM> is powered, the valves <NUM>, <NUM> are also powered (to inflate or deflate seals 10a-10f), and when the robot <NUM> is not powered, the valves <NUM>, <NUM> are also not powered (to maintain the pressure in the seals 10a-10f).

More in detail, the control unit <NUM> comprises a processor and a memory. The control unit <NUM> is for example an external computer, or a robot controller of the robot <NUM>. The memory may include a computer program, wherein the computer program comprises a computer program code to cause the control unit <NUM>, or a computer connected to the control unit <NUM>, to perform the method as will be described in the following. The program may be stored on a computer-readable medium, such as a memory stick or a CD ROOM. A computer program product may comprise a computer program code stored on such a computer-readable medium to perform the method as described herein, when the computer program code is executed by the control unit <NUM> or by a computer connected to the control unit <NUM>.

<FIG> illustrates the plurality of inflatable seals 10a-10f (in isolation) while connected in series by means of the tube arrangement <NUM>, according to one embodiment. The inflatable seals have different diameters to fit in the joint gap of the corresponding joint. The fourth inflatable seal 10d and the fifth inflatable seal 10e have been omitted for simplicity. The tube arrangement <NUM> includes the tubes 27a - 27f. Each tube in the tube arrangement (except the first tube 27a and the last tube 27f) connects an inflatable seal with a next closest inflatable seal. For example, the tube 27e connects the second inflatable seal 10b with the first inflatable seal 10a, and the tube 27d connects the second inflatable seal 10b with the third inflatable seal 10c.

<FIG> illustrates the plurality of inflatable seals 10a-10f (in isolation) while connected in parallel by means of the tube arrangement <NUM> including the tube <NUM>, according to another embodiment. Thus, the tube <NUM> connects all the plurality of inflatable seals 10a-10f in parallel.

In the following a corresponding method for sealing a joint gap <NUM> of a robot joint <NUM> will be illustrated with reference to the flow chart of <FIG>. It should be understood that the method may be used for sealing joint gaps <NUM> of a plurality of joints of the robot <NUM> by means of a plurality of inflatable joints <NUM>, but the method is here for simplicity explained with reference to sealing only one robot joint with an inflatable seal. The method comprises pressurizing S1 the inflatable seal <NUM> such that the inflatable seal <NUM> expands in an axial direction towards the second part <NUM> to seal the joint gap <NUM> between the first part <NUM> and the second part <NUM>. Thus, the inflatable seal <NUM> can be pressurized to provide a variable sealing of the robot joint. In one embodiment, the method comprises pressurizing S1 the inflatable seal <NUM> in synchronization with the robot operation. For example, the method comprises pressurizing S11 the inflatable seal <NUM> to a predetermined low pressure, upon receiving an indication that the robot <NUM> is working. The method may also include pressurizing S12 the inflatable seal <NUM> to a predetermined high pressure upon receiving an indication that the robot <NUM> is not working and/or is exposed to wash down. The predetermined high pressure is higher that the predetermined low pressure. The low pressure is for example atmospheric pressure.

The present invention is not limited to the above-described preferred embodiments. Various alternatives, modifications and equivalents may be used.

Claim 1:
Asystem (<NUM>) comprising:
a robot (<NUM>) having at least one robot joint (<NUM>) comprising a first part (<NUM>) and a second part (<NUM>) arranged to have a relative movement in between, and a joint gap (<NUM>) spacing the first part (<NUM>) and the second part (<NUM>) from each other, wherein the robot joint (<NUM>) comprises an inflatable seal (<NUM>) accommodated in the joint gap (<NUM>) to provide a fluid-tight sealing of the joint (<NUM>),
a control unit (<NUM>),
a valve arrangement (<NUM>), and
a tube arrangement (<NUM>) fluidly connected to a source of pressurized fluid and to the inflatable seal (<NUM>), wherein the control unit (<NUM>) is programmed to pressurize the inflatable seal (<NUM>) by means of the valve arrangement (<NUM>) and the tube arrangement (<NUM>) such that the inflatable seal (<NUM>) expands in an axial direction towards the second part (<NUM>) to seal the joint gap between the first part (<NUM>) and the second part (<NUM>),
characterized in that the control unit (<NUM>) is configured to control the valve arrangement (<NUM>) to pressurize the inflatable seal (<NUM>) in synchronization with the robot operation, such that the inflatable seal (<NUM>) is pressurized to a predetermined low pressure when the robot (<NUM>) is working, and to a predetermined high pressure when the robot (<NUM>) is exposed to high pressure wash down and/or is shut down,
wherein the predetermined high pressure is higher than the predetermined low pressure.