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 preferably have a complete stainless-steel housing or 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 robot and cause it to fail.

Even if the robot is provided with a stainless-steel housing, the joints may be a source to contamination. Typically, the robot is provided with rotary seals inside the robot that seal the motors and gears. However, the other parts of the robot that are not sealed may suffer from severe corrosion from the inside in the washdown environment. When washdown fluids (e.g. acid, alkaline or chlorinated liquids) and other materials from e.g. food processing get inside the robot, it will accelerate corrosion of the robot. Therefore, the joints of a robot should be sealed such that no fluid or material can enter the joints during working or wash down.

From the article "<NPL>, it is known to provide a robot with a stainless-steel material. It is described to use a spring-energized PTFE face seal to seal robot joints, but it is not in detail described how the seal is implemented.

<CIT> discloses a device for a robot comprising a first part and a second part rotatable in relation to one another. The device further comprises an outer seal arranged between the first part and the second part. The outer seal is in contact with an inner limiting surface of the first part and an outer limiting surface of the second part. The outer seal <NUM> may be made of a material compatible with foods.

<CIT> discloses a radial shaft seal comprising two housing parts rotatable relative to one another and forming a chamber. The radial shaft seal further comprises a radial packing ring of V-shaped cross-section which is arranged so as to float in lubricant in the annular chamber.

It is an object of the disclosure to alleviate at least some of the drawbacks with the prior art. It is a further object of the disclosure to provide a robot joint with a sealing that is designed for hygienic environments. It is a further object to provide a robot joint with a sealing that securely withstands external pressure. It is another object to provide a robot joint with a sealing that is durable. It is a further object to provide a sealing arrangement of a robot to a comparably low cost.

According to the invention, the disclosure relates to a robot joint comprising a first robot part and a second robot part arranged to have a relative movement in between, a joint gap separating the first robot part and the second robot part from each other, and a seal arrangement for sealing the joint gap against external impact. The seal arrangement comprises a first side element being part of the first robot part and immobile in relation to the same, and a gap element extending across the joint gap. One of the first side element and the gap element comprises a first surface in a food grade material, and the other one of the first side element and the gap element comprises a first sealing element configured to be in sliding contact with the first surface.

The invention provides a sealing of a robot joint that is designed for hygienic environments as it is provided with a food grade material surface that is the contact surface for the sealing element. Food grade materials are materials that are considered safe to be in contact with food i.e. materials that do not contaminate the food with substances harmful or potentially harmful for human. Also terms like "food contact materials" and "hygienic materials" are used to refer to food grade materials. If it is not obvious what materials shall be considered as food grade materials, the directives of the U. Food and Drug Administration (FDA) should be taken into consideration.

In some embodiments, the first side element is integral with the first robot part. As the external surfaces of the first robot part also need to be in food grade material, the first surface can be provided by locally treating, e.g. by hardening and/or polishing, the first robot part to achieve an appropriate contact surface for the sealing element. This solution implies that the first side element comprises the first surface, and the gap element comprises the first sealing element.

In some embodiments, the first robot part comprises a first robot interface configured to receive the first side element. Considering solutions where the first side element comprises the first surface (and the gap element comprises the first sealing element), as local treatment of the first robot part may be expensive, it may be advantageous to provide the first side element comprising the first surface as a separate insert configured to be fixedly attached to the first robot interface. Considering solutions where the first side element comprises the first sealing element, it is a quite obvious alternative to provide the first robot part with an interface fixedly receiving the first side element.

According to the invention, the seal arrangement comprises a second side element being part of the second robot part and immobile in relation to the same, one of the second side element and the gap element comprising a second surface in a food grade material, and the other one of the second side element and the gap element comprising a second sealing element configured to be in sliding contact with the second surface. By providing the seal arrangement with two interfaces having a sliding contact instead of one, the speed between the respective sealing elements and surfaces can be reduced to half.

In some embodiments, the second side element is integral with the second robot part.

In some embodiments, the second robot part comprises a second robot interface configured to receive the second side element.

In some embodiments, the first robot part comprises a first recess partly accommodating the gap element.

In some embodiments, the second robot part comprises a second recess partly accommodating the gap element.

In some embodiments, the first side element comprises the first surface, and the gap element comprises the first sealing element.

In some embodiments, the second side element comprises the second surface, and the gap element comprises the second sealing element.

In some embodiments, the gap element comprises the first surface, and the first side element comprises the first sealing element.

In some embodiments, the gap element comprises a second surface in a food grade material, and the second side element comprises the second sealing element.

In some embodiments, the food grade material comprises hardened stainless-steel.

In some embodiments, the first surface and/or the second surface has a surface hardness of at least <NUM> HV0. <NUM>, such as at least <NUM> HV0. <NUM>, at least <NUM> HV0. <NUM>, or at least <NUM> HV0.

In some embodiments, the first surface and/or the second surface has a surface roughness expressed as an Ra value of at most <NUM>,<NUM>, such as at most <NUM>,<NUM>, at most <NUM>,<NUM>, or at most <NUM>,<NUM>.

In some embodiments, an energizing mechanism is configured to increase contact pressure between the first surface and the first sealing element.

In some embodiments, the energizing mechanism is integrated in the gap element.

To manage high hygienic design criteria, for example for food equipment, the disclosure proposes a robot joint that is provided with a seal arrangement comprising at least one hardened stainless-steel surface. The robot joint comprises a first robot part and a second robot part arranged to have a relative movement in between. The robot where the robot joint is arranged is according to one embodiment provided with a stainless-steel housing, to reduce corrosion to the robot. To allow the relative movement between the first robot part and the second robot part, there is a gap in the stainless-steel housing at the robot joint. This gap, hereinafter referred to as a "joint gap", is thus provided with a seal arrangement meeting the water protection level stipulated by IP69K. The sealing is hygienic as the joint gap will be efficiently tightened.

The at least one hardened stainless-steel surface is hardened, typically by a hardening process, and arranged in sliding contact with a respective sealing element or sealing elements. Thereby, the at least one hardened stainless-steel surface will not wear down easily, and it will give a reduced friction towards the face seal compared to if the stainless-steel surface was not hardened. More in detail, the hardening process will increase surface hardness to <NUM>-<NUM> HV0. <NUM> (microhardness, HV0. <NUM> refers e.g. to the "Vickers" test method). Thus, hardened stainless-steel as referred to herein has, according to one embodiment, a surface microhardness of <NUM>-<NUM> HV0.

In the following robot joints comprising seal arrangements according to different embodiments, and robots comprising one or several such robot joints, will be described.

First, some exemplary robots will be described, with reference to <FIG> illustrate an industrial robot <NUM> with six 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 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 robot part <NUM> and second robot part <NUM> (<FIG>). The first robot part <NUM> is typically arranged stationary in relation to the driving motor of the axis, and the second robot part <NUM> is arranged to rotate together with the arm or wrist in relation to the driving motor. Thus, the second robot part <NUM> will rotate in relation to the first robot part <NUM> when the joint is operated. The first robot part <NUM> and the second robot part <NUM> are thus rotatable in relation to each other. Between the first robot part <NUM> and the second robot part <NUM> there is a joint gap <NUM> (<FIG>), and a gap element in the form of a face seal <NUM> is arranged to seal the joint gap <NUM>. Thus, the face seal <NUM> is arranged to seal the first robot part <NUM> and the second robot part <NUM>. In the robot <NUM> of <FIG>, each joint 20a, 20b, 20c, 20d, 20e, 20f is sealed with a respective face seal 10a, 10b, 10c, 10d, 10e, 10f. It should be understood that a robot may comprise more or less joints than six, and thus more or less face seals than six. It should also be understood that the number of face seals may be less than the number of joints i.e. not every joint needs to comprise a face seal.

<FIG> illustrates a robot <NUM> with a fork structure, also referred to as a "fork robot". The fork robot <NUM> essentially comprises the same parts as the robot <NUM> in <FIG>, except that it has a double second axis <NUM> with two joints 20b1, 20b2, a double third axis <NUM> with two joints 20c1, 20c2 and a double link that connects the respective double second axis <NUM> and the double third axis <NUM>. The fork robot <NUM> may have an increased stability compared to the robot <NUM> in <FIG>. Each joint 20b1, 20b2 of the double second axis <NUM> may be driven by an individual driving mechanism. Each joint 20c1, 20c2 of the double third axis <NUM> may be driven by an individual driving mechanism. Each joint 20b1, 20b2, 20c1, 20c2 is sealed with a respective face seal 10b1, 10b2, 10c1, 10c2. However, it should be understood that also here the number of face seals may be less than the number of joints i.e. not every joint needs to comprise a face seal.

<FIG> illustrates a cross-section of a face seal <NUM> according to a first embodiment, when provided in a robot joint <NUM>. The robot joint <NUM> may be any of the robot joints as explained herein. The first robot part <NUM> of the robot joint <NUM> defines a first hardened stainless-steel surface in the form of a first inner face 22a limiting the joint gap <NUM>. The second robot part <NUM> of the robot joint <NUM> defines a second hardened stainless-steel surface in the form of a second inner face 24a limiting the joint gap <NUM>. The inner faces 22a, 24a are typically radial faces, thus they extend in a radial direction from the motor shaft of the axis. In one embodiment, the first robot part <NUM> comprises an area hardened by a hardening process to constitute a first side element <NUM>. Then, the first side element <NUM> comprising the first inner face 22a is integral with the first robot part <NUM>. In another embodiment the first robot part <NUM> comprises a first robot interface <NUM> (<FIG>) configured to receive the first side element <NUM>, as will be described later with reference to <FIG>. Then, the first side element <NUM> comprising the first inner face 22a is non-integral with the first robot part <NUM>. In one embodiment, the second robot part <NUM> also comprises an area hardened by a hardening process to constitute a second side element <NUM>. Then, the second side element <NUM> comprising the second inner face 24a is integral with the second robot part <NUM>. In another embodiment the second robot part <NUM> comprises a second robot interface <NUM> (<FIG>) configured to receive the second side element <NUM>, as will be described later with reference to <FIG>. Then, the second side element <NUM> comprising the second inner face 24a is non-integral with the second robot part <NUM>.

The face seal <NUM> according to the first embodiment comprises an annular body designed to have a radial jacket with a flange. In cross-section, the face seal <NUM> may be seen as having the general shape of a "T", where the horizontal leg of the "T" forms first and second flange parts <NUM>, <NUM>, and the vertical leg is split into two legs forming the radial jacket. The upper side of the "T" makes up the external side of the face seal <NUM>, that is designed to front the exterior of the robot <NUM>, <NUM>. The face seal <NUM> has two dynamic sealing elements in the form of a first sealing face <NUM> and a second sealing face <NUM>, thus the outer sides of the radial jacket of the "T". The first sealing face <NUM> is arranged in sliding contact with the first inner face 22a of the first robot part <NUM>. The second sealing face <NUM> is arranged in sliding contact with the second inner face 24a of the second robot part <NUM>.

In order to hold the face seal <NUM> in place in the joint gap <NUM> and make sure the face seal <NUM> is not pushed into the joint gap <NUM> when acted upon by external pressure, the first robot part <NUM> is provided with a first recess <NUM> that accommodates the first flange part <NUM>. In other words, the joint gap <NUM> defines a first recess <NUM> in the first robot part <NUM> towards the exterior of the robot joint <NUM>, and the face seal <NUM> is partly accommodated in the first recess <NUM>. Here, the second robot part <NUM> is provided with a second recess <NUM> that accommodates the second flange part <NUM>. In other words, the joint gap <NUM> defines a second recess <NUM> in the second robot part <NUM> towards the exterior of the robot joint <NUM>, and the face seal <NUM> is partly accommodated in the second recess <NUM>. In an alternative embodiment, the joint <NUM> comprises only the first recess <NUM> arranged to accommodate only the first flange part <NUM> of a respective face seal <NUM> not comprising the second flange part <NUM>. The first and second recesses <NUM>, <NUM> may have a slightly larger axial dimension than the first and second flange parts <NUM>, <NUM>, such that the first and second flange parts are allowed to be slightly compressed by external pressure and expand axially.

To make sure the face seal <NUM> is held in a tight fit in the joint gap <NUM>, the face seal <NUM> comprises an energizing mechanism <NUM> configured to increase contact pressure between the face seal <NUM> and the first robot part <NUM>. Here, the energizing mechanism <NUM> is configured to increase contact pressure also between the face seal <NUM> and the second robot part <NUM>. The energizing mechanism is for example a spring element or an elastic tube that is arranged in the radial jacket. The energizing mechanism <NUM> is in contact with inner sides of the jacket, to push the first sealing face <NUM> towards the first inner face 22a of the first robot part <NUM> and the second sealing face <NUM> towards the second inner face 24a of the second robot part <NUM>.

<FIG> illustrates a cross-section of a face seal <NUM> according to a second embodiment, when provided in a robot joint <NUM>. The robot joint <NUM> may be any of the robot joints as explained herein. The reference numbers that are the same as in <FIG> refer to the same respective features and will not be repeated here. The face seal <NUM> according to the second embodiment generally has the same function as the face seal <NUM> according to the first embodiment. However, in this embodiment the first recess <NUM> and the second recess <NUM> are shaped to allow the face seal to expand into the first recess <NUM> and the second recess <NUM> in an angular manner, when the face seal <NUM> is exposed to external pressure against the external side of the face seal <NUM>. Also, the energizing mechanism <NUM> has a cross-section of a "V". The energizing mechanism <NUM> is at least partly arranged inside the jacket of the face seal, where the upper part of the "V" rests against an internal side, that is opposite the external side, of the face seal <NUM>. The outer sides of the "V" are in contact with inner sides of the jacket, to push the first sealing face <NUM> towards the first inner face 22a of the first robot part <NUM> and the second sealing face <NUM> towards the second inner face 24a of the second robot part <NUM>. When pressure is exerted on the exterior side of the face seal <NUM>, the face seal <NUM> will be pushed into the first recess <NUM> and the second recess <NUM>, increase the contact pressure and area of the contact surfaces and thus make the sealing even more secure.

The face seal <NUM> should be made of a material that is FDA-compliant. For example, the face seal <NUM> may be made of a polytetrafluoroethylene (PTFE) based material with approved additives, or Ultra-high-molecular-weight polyethylene (UHMWPE) based material with approved additives.

<FIG> illustrates a cross-section of an exemplary robot joint <NUM>, here a second robot joint 20b, 20b1 of the robots <NUM>, <NUM>, provided with a face seal <NUM>.

In this exemplary embodiment, the first robot part <NUM> of the robot joint <NUM> comprises a first robot interface <NUM> and a first side element <NUM> which is non-integral with the first robot part <NUM>. The first robot interface <NUM> is here a stationary part of the joint <NUM>. The first robot interface <NUM> comprises part of a first housing, or the entire first housing, of the stationary part of the corresponding axis. As shown in the <FIG>, within the first housing is arranged a driving mechanism comprising a motor <NUM> driving a driving shaft that is arranged to a transmission <NUM>. Between the motor <NUM> and the transmission <NUM>, there is oil <NUM>. The second robot part <NUM> of the robot joint <NUM> comprises a second robot interface <NUM> and a second side element <NUM> which is non-integral with the second robot part <NUM>. The second robot interface <NUM> is here a rotary part. The second robot interface <NUM> rotates with the rotational motion of the driving shaft around the axis <NUM>. The second robot interface <NUM> comprises part of a second housing, or the entire second housing, of the rotary part of the corresponding axis. The second housing is connected to the gear box <NUM>. The rotary part comprises a lid <NUM> that closes the rotary part.

As understood from the figures, the face seal <NUM> is annular and is arranged to seal the robot joint <NUM> towards the exterior of the robot. The external side(s) of the face seal <NUM> may be aligned with the external sides of the robot joint <NUM>, that are in direct proximity with the joint gap <NUM>.

Now reference is made to <FIG> that illustrates an enlarged view of one cross-section of the face seal <NUM> and the first and second side elements <NUM>, <NUM> illustrated in <FIG>. As already illustrated in <FIG>, there are first and second side elements <NUM>, <NUM> between the face seal <NUM> and the first robot interface <NUM> and the second robot interface <NUM>, respectively. The face seal <NUM> may be arranged concentric between the first side element <NUM> and the second side element <NUM>. Alternatively, the robot joint <NUM> may comprise only one of the first and second side elements <NUM>, <NUM>. The face seal <NUM> will then be in direct contact with the first robot interface <NUM> or the second robot interface <NUM> on the side that does not comprise a side element <NUM>, <NUM>.

The face seal <NUM>, the first side element <NUM> and/or the second side element <NUM> may be referred to as a seal arrangement. The first side element <NUM> is arranged between the first robot interface <NUM> and the face seal <NUM>. Thus, the first side element <NUM> is designed to bridge the first robot interface <NUM> and the face seal10. The first side element <NUM> comprises an annular body. The first side element <NUM> has a first inner face 22a. The first inner face 22a is a hardened stainless-steel surface. The face seal <NUM> is arranged such that the first sealing face <NUM> of the face seal <NUM> is in sliding contact with the first inner face 22a. The first side element <NUM> also comprises a first outer face 22b arranged to be attached to the first robot interface <NUM>. The first side element <NUM> further has an external side that faces the exterior of the robot joint <NUM>. The first side element <NUM> is attached to the first robot interface <NUM> by means of a first bolt <NUM>.

The second side element <NUM> is arranged between the second robot interface <NUM> and the face seal <NUM>. Thus, the second side element <NUM> is designed to bridge the second robot interface <NUM> and the face seal <NUM>. The second side element <NUM> comprises an annular body. The second side element <NUM> has a second inner face 24a. The second inner face 24a is a hardened stainless-steel surface. The face seal <NUM> is arranged such that the second sealing face <NUM> of the face seal <NUM> is in sliding contact with the second inner face 24a. The second side element <NUM> also comprises a second outer face 24b arranged to be attached to the second robot interface <NUM>. The first side element <NUM> further has an external side that faces the exterior of the robot joint <NUM>. The second side element <NUM> is attached to the second robot interface <NUM> by means of a second bolt <NUM>.

As the first and second side elements <NUM>, <NUM> that are provided with the hardened stainless-steel surfaces are non-integral with the first robot part <NUM>, the cost may be reduced. This because the hardening typically is payed per kilo that should be hardened, and the non-integral first and second side elements <NUM>, <NUM> have a lower weight than the first robot interface <NUM> and the second robot interface <NUM>. One purpose of the non-integral first and second side elements <NUM>, <NUM> is thus to decrease the amount om stainless-steel material to be hardened.

The first outer face 22b has a plurality of first incisions <NUM>, e.g. annular incisions, where grinding particles etc. may be collected. The second outer face 24b has a plurality of second incisions <NUM>, e.g. annular incisions, where grinding particles etc. may be collected. Alternatively, the first outer face 22b and/or the second outer face 24b may only have one annular incision, respectively.

<FIG> illustrates a cross-section of a robot joint <NUM> provided with a face seal <NUM> according to a third embodiment, which is not part of the invention. The robot joint <NUM> differs from the previous embodiments in that it only has dynamic sealing element on one side of the joint gap <NUM>. As in the other embodiments, the first robot part <NUM> defines a first inner face 22a limiting the joint gap <NUM>, and the first inner face 22a is a hardened stainless-steel surface. The face seal <NUM> is arranged in the joint gap <NUM> to seal the joint gap <NUM>, wherein the face seal <NUM> comprises a first sealing face <NUM> that is arranged in sliding contact with the first inner face 22a of the first robot part <NUM>. The first sealing face <NUM> has a third incision <NUM>, e.g. an annular incision, where grinding particles etc. may be collected. The face seal <NUM> is fastened or bonded to the second robot part <NUM>, for example by means of a third bolt <NUM>.

<FIG> illustrates a cross-section of a gap element in the form of a joint seal assembly <NUM> according to some embodiments. The joint seal assembly <NUM> is intended to be provided in a joint gap <NUM> of a robot joint <NUM> according to <FIG>. The joint seal assembly <NUM> comprises a first annular insert body <NUM>, a second annular insert body <NUM> and an annular bonding element <NUM>. The annular bonding element <NUM> is interposed concentric between the first annular insert body <NUM> and the second annular insert body <NUM>. The annular bonding element <NUM> is also bonded to the first annular insert body <NUM> and the second annular insert body <NUM>. The first annular insert body <NUM> comprises a first flange <NUM>. The second annular insert body <NUM> comprises a second flange <NUM>. The first annular insert body <NUM> and the second annular insert body <NUM> are made of hardened stainless-steel. The annular bonding element <NUM> is for example made of PTFE or UHMWPE.

<FIG> illustrates the cross-section of the joint seal assembly <NUM> in <FIG> arranged in a robot joint <NUM>. The robot joint <NUM> comprises a first robot interface <NUM> and a second robot interface <NUM> arranged to have a relative movement in between. A joint gap <NUM> separates the first robot interface <NUM> and the second robot interface <NUM> from each other. The joint gap <NUM> is provided with the joint seal assembly <NUM> in <FIG>.

As illustrated in the <FIG>, the first robot interface <NUM> is provided with a recess receiving a first sealing element in the form of a first rubber gasket <NUM>, which in this embodiment constitutes the first side element <NUM>. The first annular insert body <NUM> is provided with a first flange <NUM> received in the first rubber gasket <NUM> to provide a sliding contact thereinbetween.

The second robot interface <NUM> is provided with a recess receiving a second sealing element in the form of a second rubber gasket <NUM>, which in this embodiment constitutes the second side element <NUM>. The second annular insert body <NUM> is provided with a second flange <NUM> received in the second rubber gasket <NUM> to provide a sliding contact thereinbetween.

Claim 1:
A robot joint (<NUM>) comprising:
a first robot part (<NUM>) and a second robot part (<NUM>) arranged to have a relative movement in between,
a joint gap (<NUM>) separating the first robot part (<NUM>) and the second robot part (<NUM>) from each other, and
a seal arrangement for sealing the joint gap (<NUM>) against external impact, the seal arrangement comprising a first side element (<NUM>) being part of the first robot part (<NUM>) and immobile in relation to the same, and a gap element (<NUM>, <NUM>) extending across the joint gap (<NUM>),
wherein one of the first side element (<NUM>) and the gap element (<NUM>, <NUM>) comprises a first surface (22a) in a food grade material,
wherein the other one of the first side element (<NUM>) and the gap element (<NUM>, <NUM>) comprises a first sealing element (<NUM>, <NUM>) configured to be in sliding contact with the first surface (22a),
wherein the seal arrangement comprises a second side element (<NUM>) being part of the second robot part (<NUM>) and immobile in relation to the same, one of the second side element (<NUM>) and the gap element (<NUM>, <NUM>) comprising a second surface (24a) in a food grade material, and the other one of the second side element (<NUM>) and the gap element (<NUM>, <NUM>) comprising a second sealing element (<NUM>, <NUM>),
characterized in that the second sealing element (<NUM>, <NUM>) is configured to be in sliding contact with the second surface (24a).