POWER TRANSMISSION DEVICE FOR A FORCE MEASURING DEVICE, IN PARTICULAR A WEIGHING DEVICE

Description

[0001] The invention relates to a current transmission device for a force measuring device, in particular a weighing device.

[0002] When transmitting currents or electrical energy between two relatively movable sections of a force measuring device, appropriate safety measures must be taken when using the force measuring device in a potentially explosive atmosphere. Such a force measuring device can, for example, be a weighing device comprising a conveyor belt with an electric drive that acts as a preload on a load cell arranged in a housing of the weighing device.Usually, both electrical supply lines are provided, which are led, for example, from a power supply unit provided in the housing of the weighing device or a power supply unit arranged on the housing of the weighing device in a separate housing to the electrical drive of the conveyor belt, and communication lines which are led from a control unit provided in the housing of the weighing device to the electrical drive of the conveyor belt.

[0003] Various methods are known for making such a weighing device explosion-proof. For example, the entire housing can be filled with a protective gas atmosphere. Since a weighing device always has to have a load receptor or an element coupled to it leading out of the housing with as little contact as possible, i.e. with a low force shunt, it would be necessary to provide either a completely tight seal between the load receptor with the lowest possible force shunt, for example a bellows, or to provide a sufficiently small gap between the load receptor and the feedthrough opening, which can also be sealed using a labyrinth seal. With a completely tight seal, the housing can be (statically) filled with a protective gas atmosphere.If a gap remains between the load receptor and the feedthrough opening, a continuous inert gas supply (dynamic inert gas atmosphere) must be maintained to prevent the inert gas atmosphere from diluting over time to the point where an explosive atmosphere develops. This creates a slight overpressure in the enclosure, preventing an explosive atmosphere from developing. In this case, normal room air can be used instead of an inert gas, provided that it is ensured that this room air does not contain any potentially explosive components.

[0004] Such a weighing device can also be made explosion-proof by having a pressure-resistant housing or a pressure-resistant enclosure. The housing or enclosure must withstand the pressure of any explosive mixture present within the housing and prevent the explosion from spreading to the outside. It must also be avoided that components of the housing or enclosure are ejected from the housing like projectiles in the event of an explosion of a mixture inside the housing. Furthermore, in the event of an explosion within the housing or enclosure, it must be ensured that no ignition propagates into the surrounding area, in order to prevent an explosion from occurring outside the housing in the event of an explosive atmosphere outside the housing or enclosure.If, for example, openings are provided in the housing, such as passage openings for moving components, these must be designed in such a way that no hot particles generated by an explosion can escape through such openings if the hot particles are not sufficient to ignite a potentially explosive atmosphere outside. The escaping gas must also not exceed a certain maximum temperature. To ensure this, an opening, such as an annular gap around an element passing through a housing wall, can be dimensioned in such a way that a sufficiently small cross-section is provided (the exit direction of the gas runs perpendicular to this cross-section). In addition, the exit opening must have a specified minimum length (seen in the exit direction) so that the exit temperature of the gas does not exceed a specified maximum value.

[0005] However, these measures for the explosion-proof design of a weighing device require a correspondingly high level of design effort, which increases the size of the device's housing and its weight, and is also associated with corresponding manufacturing costs. The provision of a static or dynamic protective gas atmosphere or the dynamic supply of (non-explosive) ambient air also requires corresponding effort for the protective gas supply and leads to high operating costs.

[0006] It is known to create a largely force shunt-free electrical connection between stationary components within the housing of such a weighing device and the electrical drive of the conveyor belt by routing corresponding cables through the interior of the load receptor, which is guided through the housing wall. At the lower end of the load receptor, which is located in the housing of the weighing device, an electrical circuit board is provided. This circuit board has contacts that are connected to the ends of the cables routed through the load receptor. Another, stationary circuit board is provided in the housing. This circuit board also has contacts that are connected to corresponding supply lines or control lines that come from the corresponding components inside or outside the housing.Both circuit boards have a bridge contact for each line, with two associated bridge contacts connected via a sufficiently flexible, usually short, electrical bridge in the form of a thin electrical conductor. These electrical conductors are usually uninsulated or, at most, insulated with a thin layer of varnish to ensure sufficient flexibility. This ensures sufficient mobility of the load sensor relative to a stationary area of ​​a suitable measuring sensor while simultaneously minimizing force shunts.

[0007] The sensor can, for example, be a weighing sensor that operates according to the principle of electrodynamic force compensation. This requires only extremely small or infinitesimally small deflections between the load sensor and the ground. Accordingly, the electrical bridges can be very short.

[0008] However, in this case, it would be necessary to design the entire housing of the weighing device to be explosion-proof in order to ensure explosion protection. This is because the method of signal transmission or transmission of the electrical drive power through the load receptor described above poses the risk that, in the event of a fault, such as a short circuit, arcing, or terminal discharge, could occur between the bridge conductors, which would ignite an explosive atmosphere within the housing. However, this, in turn, involves a corresponding amount of effort.Based on this prior art, the invention is based on the object of creating a power transmission device for a force measuring device, in particular a weighing device, with which the force measuring device can be designed to be explosion-proof and thus used in potentially explosive atmospheres, and which can be implemented simply and cost-effectively. Furthermore, the invention is based on the object of creating a force measuring device, in particular a weighing device, with such a power transmission device.

[0009] In the following, any device for detecting a weight force is referred to as a weighing device.

[0010] The invention solves this problem with the features of independent claims 1 and 15 respectively.

[0011] Patent document JP3771994B2 discloses a force measuring device which has a current transmission device with a connecting element 26, wherein this connecting element is not designed such that it penetrates the housing wall in a contactless and ignition-proof manner in the operating state.

[0012] The invention is based on the finding that explosion protection for a force measuring device having a housing can be ensured by not requiring the entire housing to meet explosion protection requirements, but rather by merely arranging a power transmission device according to the invention in the housing of the force measuring device or connecting it externally to the housing of the force measuring device. Such a power transmission device serves for the wired transmission of electrical energy, in particular for supplying energy to any desired components (e.g., an electric drive) and / or for wired communication (i.e., for transmitting electrical signals).

[0013] The power transmission device according to the invention has a pressure-resistant housing with a housing wall, wherein the housing can be mechanically firmly connected to the base region of the force measuring device. The base region of the force measuring device can be, for example, the housing of the force measuring device. Furthermore, the power transmission device has a connecting element which, at an outer end region protruding from the housing, can be mechanically firmly connected to the movable region of the force measuring device in an operating state. This can be, for example, a region of a load sensor protruding from the housing of the force measuring device or a component connected to it, for example a load plate located outside the housing.In the case of the above-explained example of a weighing device with a housing and a conveyor belt located outside the housing, which acts as a preload on a force transducer (for example a load cell) arranged in the housing, the conveyor belt can be arranged on such a load plate.

[0014] The connecting element protruding from the housing of the power transmission device is designed so that, during operation, it penetrates the housing wall without contact and without risk of ignition. The term "ignition-proof" means that the connecting element's penetration through the housing wall is designed in such a way that explosion protection is ensured (if necessary, taking into account relevant regulations and, if applicable, different explosion protection classes).

[0015] The connecting element of the power transmission device is designed as a movable cable passage, wherein a first cable with at least one electrical line is guided into the connecting element at the outer end region (i.e. outside the housing of the power transmission device) and extends through the connecting element. At an inner end region of the connecting element, which projects into the housing, the cable is guided into the housing. The cable is thus guided in the connecting element into the housing, wherein the lead-through of the cable through the connecting element must be designed to be at least ignition-proof. For example, the cable can be guided through a recess in the connecting element and glued into this recess. Instead of gluing, the cable can also be clamped in this recess of the connecting element using suitable design measures.Furthermore, it is possible to strip individual cable cores (hereinafter referred to as wires) of the cable sheath in a certain axial region and glue them into a recess in the connector. This prevents excess pressure developing inside the housing (in the event of an explosion) from inflating the cable sheath outside the housing and potentially causing it to burst explosively, which could even pose a risk of ignition.

[0016] It is of course also possible to route several cables, each with a single wire, or several wires (then referred to as cables), through the connecting element into the housing of the power transmission device instead of a single cable.

[0017] The passage of at least one cable through the connecting element must also be pressure-resistant to prevent the cable recess in the connecting element from being breached in the event of an explosion generating excess pressure in the housing. In this case, a flashover could occur, or parts of the cable or components for the cable passage could be detached and thrown off.

[0018] Furthermore, the housing of the power transmission device has a cable bushing fixed to the housing, which is designed for the pressure-resistant and spark-proof passage of a second cable with at least one electrical line through the housing wall. Here, too, instead of a single cable, multiple cables with a single line each can be used. The above comments apply analogously to the passage through the connecting element for the passage through the housing.

[0019] At the second end region of the connecting element, a movable contact device is provided which is mechanically firmly connected thereto, and in the housing, a housing-fixed contact device is provided which is mechanically firmly connected to the housing, wherein at least one flexible electrical contact bridge is formed between the movable contact device and the housing-fixed contact device.

[0020] The at least one line of the first cable is mechanically and electrically connected to the movable contact device and the at least one line of the second cable is mechanically and electrically connected to the stationary contact device such that an electrical and mechanical contact is formed between the at least one line of the first cable and the at least one line of the second cable via the at least one contact bridge.

[0021] This at least one flexible electrical contact bridge is designed such that the force shunt generated by the first and second cables between the base region and the movable region of a force measuring device with such a current transmission device is smaller than a predetermined threshold value. This threshold value can, of course, be selected depending on the required measurement accuracy of the force measuring device. The electrical contact bridge can be formed, for example, as a thin, flexible gold strip or from a plurality of individual fine wires.

[0022] According to one embodiment of the invention, the current transmission device is designed such that the connecting element is designed as a substantially cylindrical element and that the housing wall has a predetermined thickness in a region of a through-opening for the connecting element and the through-opening has a predetermined cross-section, which are selected such that, in the operating state, an arc-proof annular gap is formed between the connecting element and an inner wall of the through-opening.

[0023] A flame-proof annular gap requires that its cross-section (seen along the longitudinal axis of the connecting element) and its length are determined in such a way that even in the event of an explosion inside the enclosure, it is ensured that no flame-passing occurs in the space surrounding the enclosure, even if a potentially explosive atmosphere exists there. The cross-section of the annular gap can also vary along the longitudinal axis of the connecting element.

[0024] In a further embodiment, the housing may have a housing cover which is detachably connected to the housing and which is designed such that the housing cover, with an engagement region extending into the interior of the housing, cooperates with at least one stop shoulder on the outer circumference of the connecting element in such a way that a limit stop is effected with regard to the movement of the connecting element, at least with regard to a movement of the connecting element in a direction of movement out of the housing.

[0025] For this purpose, the housing cover can have a flange extending into the housing, preferably a circumferential flange, which forms the engagement area.

[0026] The at least one stop shoulder can be formed by a recess, for example a groove, in the outer circumference of the connecting element.

[0027] Such a limit stop prevents the connecting element from being ejected from its receiving opening like a projectile in the event of an explosion inside the housing of the power transmission device.

[0028] In addition to the stop shoulder that limits this movement out of the housing, a further stop shoulder can be provided that prevents the connecting element from being moved too far into the housing. In this way, in particular, destruction of the at least one contact bridge or even the movable or housing-fixed contact device can be avoided.

[0029] For example, a groove in the outer circumference of the connecting element can realize both stop shoulders simultaneously.

[0030] To simplify assembly of the power transmission device, an annular mounting element can be provided which encompasses the connecting element and is designed to be displaceable thereon in the direction of a longitudinal axis of the connecting element between an adjustment position and an operating position. Furthermore, for this purpose, the access opening for the connecting element can be designed as an engagement area for the annular mounting element in an area directed outwards with respect to the housing. The mounting element and the engagement area can be designed and interact with the mounting element in the adjustment position in such a way that the connecting element is positioned in the housing such that, with the exception of the engagement area, the arc-proof annular gap is formed between the connecting element and an inner wall of the access opening.In this adjustment position, the connecting element can be mechanically connected to the movable portion of a force measuring device, and the housing of the current transmission device can be mechanically connected to the base portion of the force measuring device in such a way that, after disengaging the mounting element and the engagement portion, a (essentially exclusively axial) movement of the connecting element in the through-opening is possible. In this operating position, the mounting element releases the connecting element, i.e., the connecting element passes through the through-opening without contact.

[0031] This allows for a very simple installation of the power transmission device on or in a force measuring device, whereby the highly precise adjustment of the connecting element with respect to the housing of the power transmission device can be ensured.

[0032] According to one embodiment of the invention, the mounting element can be designed to be lockable in the operating position and / or the adjustment position on the connecting element. By locking it in the operating position, the mounting element can remain attached to the connecting element in the operating state without interfering with the free movement of the connecting element in the access opening.

[0033] The mounting element can also be designed in such a way that it forms a labyrinth seal in the operating position, i.e. it becomes part of a labyrinth seal which protects the annular gap in particular against the ingress of water, dust or other particles.

[0034] According to a further embodiment of the invention, the mounting element is encompassed by a ring element which is movable from a mounting position into a working position, wherein the ring element is positioned offset in the working position relative to the mounting element in the direction of the housing and forms the labyrinth seal with the mounting element and the housing.

[0035] The ring element can also be locked in the working position relative to the mounting element and thus also relative to the connecting element. This working position can also be selected such that the lower end face of the ring element, i.e. the end face of the ring element facing the outside of the housing, forms a stop for the movement of the connecting element into the housing.

[0036] Furthermore, the housing can have a protruding flange surrounding the access opening to help form the labyrinth seal, which flange is preferably encompassed by the ring element, with an annular gap being formed between an inner wall of the ring element and an outer wall of the flange. This annular gap can also form part of the labyrinth seal.

[0037] According to a further embodiment, the movable contact device and the housing-fixed contact device can each be designed as a printed circuit board. The at least one flexible electrical contact bridge between the respective contacts of the printed circuit boards can be designed as a flexible electrical conductor, in particular as a metallic conductor, for example, a gold strip.

[0038] In order to simplify the assembly of the power transmission device according to the invention, the circuit boards forming the movable contact device and the housing-fixed contact device can be mechanically connected to one another in an assembled state. For example, after the connecting element has been inserted into the housing, the two connected circuit boards can be connected to the housing or to the inner end of the connecting element. The connecting element can be in a position in which the assembly element, in its adjustment position on the connecting element, engages in the input area of ​​the housing and thereby positions the connecting element relative to the housing such that the connecting element penetrates the housing without contact. The connection between the two circuit boards can then be removed without the risk of the sensitive at least one contact bridge being destroyed.

[0039] The circuit boards can be connected, in particular, via separation points, which enables the circuit boards to be manufactured as a single piece. The separation points are defined by a correspondingly narrow or thin part of the circuit boards.

[0040] The power transmission device according to the invention thus makes it possible to create a force measuring device for use in potentially explosive atmospheres, which has a simple and cost-effective design and in which an electrical connection is formed between the two relatively movable regions of the force measuring device, which generates only an extremely low force shunt. The power transmission device according to the invention has a modular design and can also be used for relatively simple retrofitting or conversion of an existing force measuring device. Furthermore, the modular design allows for use with a wide variety of force measuring device types.The power transmission device according to the invention can accommodate further electrical components that are not intrinsically safe and that are required for the force measuring device and that would have to be arranged in the housing of the force measuring device without the power transmission device according to the invention (in this case, without the use of the power transmission device according to the invention, the entire housing of the force measuring device would have to be designed to be explosion-proof).

[0041] Further embodiments of the invention emerge from the dependent claims. The invention is explained in more detail below with reference to an exemplary embodiment shown in the drawing, without this exemplary embodiment being construed as a limitation of the basic core ideas of the invention explained above. The drawing shows Fig. 1 a perspective view of a weighing device with a housing, a load plate arranged outside the housing and a force transducer arranged in the housing, the load introduction of which is mechanically coupled to the load plate; Fig. 2 a perspective view of the weighing device according to Fig.1 without the side housing wall with a power transmission device according to the invention; Fig. 3 a partially sectioned side view of the power transmission device according to Fig. 2 ; Fig. 4 a perspective view of the connecting element of the power transmission device according to Fig. 3 with a movable contact device attached thereto; and Fig. 5 a perspective view of the side housing cover of the housing of the power transmission device according to Fig. 3 .

[0042] Fig. 1 shows a perspective view of a force measuring device in the form of a weighing device 100 with a housing 102, which has a base plate 104, a circumferential side wall 106, and an upper housing wall 108. A load plate 110 is mechanically connected to three support elements that are guided through the upper housing wall 108, wherein the support elements extend through the upper housing wall 108 without contact. The corresponding openings in the upper housing wall 108 or the annular gaps formed by the inner walls of the openings and the outer walls of the support elements extending through them are each "sealed" by means of a labyrinth seal 112, whereby sealing in this case means that an annular gap with a meandering cross-section, formed by each labyrinth seal, prevents the penetration of water, dust, and other particles.The passage of the supporting elements remains contactless and does not generate any force shunt.

[0043] At the Fig. 1 On the left side of the housing wall 106, a socket device 114 is provided, via which the weighing device 100 can be supplied with electrical energy and via which a unidirectional or bidirectional communication connection can be established between the weighing device 101 and a higher-level unit, for example an external control unit (not shown).

[0044] The housing 102 of the weighing device 100 is not explosion-proof. Nevertheless, the weighing device 100, as a whole, should be designed so that it can be operated in a potentially explosive atmosphere, taking the relevant regulations into account.

[0045] Fig. 2 shows the weighing device 100 from Fig. 1 without the circumferential side wall of the housing 102. As can be seen from this figure, a force transducer 116 is provided inside this housing 102, which in the illustrated embodiment operates according to the principle of electromagnetic force compensation. The force transducer 116 has a base body 118, which on the one hand comprises a base part 120 and on the other hand comprises a load introduction area 122 connected to the base part 120 via a lever mechanism. The load introduction area 122 has a support plate 124 on its upper side, which in turn is connected to the support elements described above, which are guided through the upper housing wall 108 without contact. The support plate 124 can, for example, be screwed to the load introduction area 122.

[0046] Thus, the force transducer 116 can detect the weight force acting on the load plate 110. The load plate 110 can be connected to and loaded by another device, for example, a conveyor device (not shown), such as an electrically driven conveyor belt. The electrical drive of the conveyor belt must be supplied with electrical energy. In such a case, it is necessary to establish a communication connection between the weighing device 100 or an external unit connected to the weighing device via the socket device 114. For this purpose, a cable connection is typically used between the weighing device and the mechanically connected further device. The term "cable connection" is used here to mean any type of wired connection for the transmission of electrical currents (regardless of the purpose of the currents). Fig. 1 and 2 show a cable 126 of such a cable connection in part, wherein only the part of the cable 126 which passes through the upper housing wall 108 of the housing 102 of the weighing device 100 is shown.

[0047] Fig. 2 shows a power transmission device 200 arranged in the interior of the housing 102, which has a housing 202. The housing 202 has a closure cover 204 provided on the front side wall, which is connected to the housing 202 by a plurality of screws. On its right side wall, the housing 202 has a cable feedthrough 206 fixed to the housing, wherein Fig. 2 only a connecting part 208 connected to the housing is shown, without a cable guided through and held in the connecting part 208. This cable guided into the housing 202 of the power transmission device 200 can, for example, be connected to the socket device 114, so that by connecting the socket device 114, a corresponding line connection can be established from an external unit (not shown) to the power transmission device 200 and from there to the unit connected to the load plate 110, for example, a conveyor belt.

[0048] The power transmission device 200 makes it possible to connect the cable (not shown) guided into the housing 202 on its side wall via the cable bushing 206 fixed to the housing to the cable 126 in such a way that only a very small force shunt is caused with respect to the parts of the force transducer 116 (and thus also of the weighing device 100) that are movable relative to one another.

[0049] Fig. 3 shows a sectional view of the power transmission device 200 in a (relative to the illustration in Fig. 2 ) vertical center plane. First of all, it can be seen from this figure that the housing 202 has very thick walls, which ensure the pressure resistance of the housing. The connecting part 208 of the cable feedthrough 206 fixed to the housing is screwed into the right side wall of the housing, whereby this screw connection must of course also be pressure-resistant in order to prevent the connecting part 208 from being ejected from the housing 202 like a projectile in the event of an explosion within the housing 202. The cable (not shown) which is passed through the connecting part 208 must be connected to the connecting part 208 in a way that is at least impermeable to ignition. As already explained above, this can be achieved by a clamping mechanism (not shown in detail) or by gluing or potting.Since the cable usually has several lines combined therein, the sheath can also be removed in an axially inner region of the connecting part 208 to improve the connection between the cable and the connecting part 208, so that the individual lines can each be connected individually to the connecting part 208, for example by gluing or potting.

[0050] In the interior of the housing 202, a contact device 210 is also arranged, which is fixed to the housing and can be fixed, for example, by means of two screws 212 (in Fig. 2 (only the left screw 212 is shown) can be screwed to the housing. The housing-mounted contact device 210 has connection contacts 210a, which can be connected to the ends of the wires contained in the cable. This can be done by soldering or any clamping mechanism.

[0051] A through-opening 214 is formed in the upper wall of the housing 202, through which a connecting element 216 extends. The connecting element 216 is guided through the through-opening 214 in a contactless and arc-proof manner, at least in an operating state in which the connecting element 216 is connected to the movable part of the weighing device 100, in particular the support plate 124 and thus also the load plate 110. For this purpose, the cross-section of the through-opening 214 is dimensioned with respect to the cross-section of the connecting element 216 (in the region of the through-opening 214) such that, in the operating state, an arc-proof annular gap exists between the inner wall of the through-opening 214 and the outer wall or outer circumference of the connecting element 216.The operating state therefore naturally requires a sufficiently precise positioning of the connecting element 216 relative to the housing 202 and thus the through opening 214.

[0052] As from Fig. 3 As can be seen, the connecting element 216 can be cylindrical, in particular circularly cylindrical, at least in the region with which the connecting element 216 extends through the through-opening 214. This results in a simple structural design, since the through-opening 214 can be designed as a bore.

[0053] In its upper region, the connecting element 216 can have a receiving area for a further connecting part 208, which can have the same structural design as the connecting part 208 of the housing-fixed contact device 210. This results in a simple structural design. Of course, this area of ​​the connecting element 216 can also be designed in any other suitable manner. In this case, too, the connecting part 208 is held pressure-tight in the connecting element 216.

[0054] The connecting element 216 is designed as a cable passage and for this purpose has a recess 218 which extends through the connecting element 216 over its entire length, wherein the upper region of the recess 218 is designed to receive the connecting part 208 with an internal thread which cooperates with an external thread of the connecting part 208.

[0055] The connecting part 208, which is screwed into the upper area of ​​the connecting element 216, receives a cable 220 of the cable connection 126 ( Fig. 2 ) and guides it into the recess 218 in a manner that is at least safe from ignition. Of course, the cable 220 can also have a plurality of lines, which, as described above, can also be individually fixed in the connecting part 208.

[0056] The cable 220 or the respective lines are guided through the recess 218 and protrude with their inner ends into the interior of the housing 202. The inner area of ​​the connecting element 216 also protrudes into the interior of the housing 202, so that, as can be seen from Fig. 3 As can be seen, a movable contact device 222 can be attached to the inner end of the connecting part 216. This attachment can also be effected by means of screws 224.

[0057] The movable contact device 222 also has connecting contacts 222a, which are connected to the ends of the at least one line (not shown) contained in the cable 220. The connection can again be made, for example, by soldering or suitable clamping mechanisms. The movable contact device 222 is thus movable together with the connecting element 216, whereby relative movements can be performed with respect to the housing 202. The movement path depends on the design of the force transducer 116. If this is designed as a force transducer according to the principle of electromechanical force compensation, only infinitesimally small movement paths need to be performed, since this measuring principle is based on holding the load sensor in a predefined position as far as possible, whereby the current required for this represents a measure of the weight force to be measured.

[0058] The connection contacts 210a of the housing-fixed contact device 210 and the connection contacts 222a of the movable contact device 222 are connected via contact bridges 226, with each contact bridge 226 connecting a connection contact 210a to an associated connection contact 222a. Accordingly, a line of the cable routed into the housing 202 via the cable feedthrough 206 is connected to an associated line of the cable routed into the housing 202 via the connecting element 216. To minimize the risk of force shunts, the contact bridges 226 consist of very flexible electrical conductors, such as gold wires or gold strips. These can be connected to the connection contacts 222a and 210a, respectively, by bonding, soldering, or the like. If a contact bridge 226 is designed to carry higher currents, two or more wires can also be connected to the respective connection contacts.

[0059] The contact devices 210 and 222 can, as in Fig. 3 As shown, the connecting contacts 210a and 222a can be designed as printed circuit boards, wherein the connecting contacts 210a and 222a can be designed in the form of corresponding conductor tracks or conductor track regions. Connecting contacts 210a and 222a can also each have starting regions and end regions that can be connected via one or more conductor tracks. Thus, the regions in which the ends of the contact bridges are connected to the connecting contacts can be located at a different location than the regions of the connecting contacts that are connected to the corresponding ends of the lines routed in the cables.

[0060] At the Fig.3 In the embodiment shown, the circuit boards of the contact devices 210 and 222 are still connected to one another via connecting webs 228. This is because the circuit boards of the contact devices were manufactured in this exemplary embodiment as a single circuit board having a first region that forms the contact device 210 and a second region that forms the contact device 222. This simplifies the assembly of the power transmission device 200. For example, the still one-piece circuit board that forms the contact devices 210 and 222 can first be inserted into the housing 202 and fastened with the screws 212. Subsequently, the ends of the lines of the cable, which is guided into the housing by means of the cable feedthrough 206, can be connected to the connection contacts 210a.The connecting element 216 can then be inserted into the through-hole 214 until the inner end of the connecting element 216 is positioned relative to the circuit board so that the circuit board can be connected to the connecting element 216 with the screws 224. In this state, the cable 220 does not yet have to be screwed into the upper area of ​​the connecting element 216 together with the connecting part 208. However, this can also be the case.

[0061] In this assembled state of the connecting element 216, however, it is not yet guaranteed that the connecting element 216 protrudes through the through-opening 214 without contact, since the annular gap in question has extremely small dimensions and the fastening of the connecting element 216 via the circuit board forming the contact devices 210 and 222 alone is not sufficient for such exact positioning.

[0062] For the purpose of such precise positioning, a ring-shaped mounting element 230 is provided on the connecting element 216, which engages around the connecting element and is axially displaceable (in the direction of a longitudinal axis L of the connecting element) on the connecting element 216. The mounting element 230 engages around the connecting element 216 without play but is axially displaceable, so that when the mounting element 230 is fixed, the connecting element 216 guided therein is also positioned exactly in the respective position.

[0063] As from Fig. 3 As can be seen, the housing 202 has an engagement region 232 in the region of the through-opening 214 on the upper housing wall, which engagement region is designed such that it interacts with a lower region of the mounting element 230 for an exact positioning of the mounting element 230 and thus of the connecting element 216. For this purpose, the engagement region 232 can, for example, have a circumferential annular shoulder 234 which has a vertically extending inner wall which interacts with the vertical outer wall of the lower region of the mounting element 230. This outer wall in the lower region of the mounting element 230 and the inner wall of the annular shoulder 234 can be designed exactly coaxially to the longitudinal axis L. The annular shoulder orThe (vertical) inner wall thereof, which extends coaxially to the longitudinal axis L, can be formed in a region of the housing wall that protrudes from the surface of the upper housing wall and / or in a region of the housing wall that is offset inwardly relative to the surface. Thus, precise positioning of the connecting element 216 can be achieved by bringing the lower region of the mounting element 230 into engagement with the engagement region 232.

[0064] Instead of a circumferential annular shoulder, it is of course also possible to provide elements or areas distributed only in sections around the circumference of the mounting element 230, which in an analogous manner effect an exact positioning of the connecting element 216.

[0065] The mounting element 230 can also be designed to be lockable relative to the connecting element 216, for example by means of one or more grub screws 236 which extend inwards in the wall of the mounting element 230 in the direction of the connecting element 216, perpendicular to the longitudinal axis L.

[0066] Thus, the above-described assembly of the power transmission device 200 can be supplemented as follows: After connecting the circuit board forming the contact devices 210 and 222 to the connecting element 216, the mounting element 230 can be pushed downward into the engagement area 232 and locked in this position. Subsequently, the connecting webs 228 can be separated, and the closure cover 204 can be inserted and screwed to the housing 202. Preassembled in this way, the power transmission device 200 can be stored, packaged, or installed in a weighing device 100.

[0067] The power transmission device 200 can be provided at any suitable position within the housing 102, for example, near the attachment point of the force transducer to the base plate 104 or near the load introduction area 122 or in the area of ​​a pivot joint of a lever mechanism of the force transducer 116.

[0068] In order to protect the arc-proof annular gap between the connecting element 216 and the inner wall of the access opening 214 against the penetration of particles, water, or the like, the mounting element 230, together with the engagement region 232, can form a labyrinth seal 238. In particular, the lower end face of the mounting element 230 can act as a boundary wall for the labyrinth seal 238.

[0069] As from Fig. 3 As can be seen, the mounting element 230 can be encompassed by a ring element 240, which also contributes to the formation of the labyrinth seal 238. The ring element 240 has an inner cross section that essentially corresponds to the outer cross section of the mounting element 230, so that the ring element 240 essentially tightly encloses the mounting element 230. The ring element can also be fixed to the mounting element 230 by means of a grub screw 236. In order to achieve axial positioning of the ring element 240 on the mounting element 230, the mounting element 230 can have two recesses 242, into which the grub screw 236 in the ring element 240 can engage. A first recess 242, which is in Fig. 4 visible, can serve to lock the ring element 240 in an upwardly pushed state on the mounting element 230 so that the connecting element 230 can engage in the input area 232. In a downwardly pushed state, as in Fig. 4 As shown, the grub screw 236 in the ring element 240 engages in a further recess in the mounting element 230 to lock the ring element in a downwardly pushed position on the connecting element 216. In this position, the labyrinth seal 238, as shown Fig. 3 visible, formed by the engagement area 232, the annular shoulder 234, the lower end face of the mounting element 230 and the annular element 240.

[0070] In this downwardly pushed working position, the lower end face of the ring element 240 facing the upper housing wall can also act as a limit stop to limit axial movement of the connecting element 216 into the housing 202.

[0071] Such a limitation of the displacement path for the connecting element 216 can also be achieved by the closure cover 204 having a flange 204a that projects substantially horizontally into the housing interior and engages in a groove 244 of the connecting element provided in the circumference of the region extending into the housing interior. The horizontally extending surfaces of the groove 244 have an axial spacing that, relative to the thickness of the flange 204a, is selected such that the connecting element 216 can execute a sufficiently large axial displacement movement.

[0072] The installation of the power transmission device 200 in a force measuring device, for example in the form of the weighing device 100, can be carried out as described below: The pre-assembled power transmission device 200 as explained above is connected to the stationary area of ​​the weighing device 100 by means of the mounting element 230 engaging in the engagement area 234 (in an adjusted and possibly locked state of the power transmission device 200). For this purpose, the housing 202 can be connected to the base plate 104 of the housing 102 of the weighing device 100. This can be done, for example, by screwing or the like. To connect the connecting element 216 to the load sensor or load introduction area of ​​the force sensor 116, as can be seen from Fig. 2As can be seen, an upper head region of the connecting element 216, which is essentially circularly cylindrical in shape, has two surfaces 246 running parallel to one another in a suitable axial region. With this axial region, the head region of the connecting element 216 can engage in a slot of a fork-shaped region in the carrier plate 124. A nut 248 can then be screwed onto the upper head region of the connecting element in order to mechanically and firmly connect the connecting element 216 to the carrier plate 124. The upper housing wall 108 of the housing 102 can then be placed on top, with the upper region of the connecting element 216 and three further elements extending upward from the carrier plate 124 passing through the upper housing wall 108.Subsequently, the labyrinth seals 112 can be manufactured both in the area where the upper portion of the connecting element 216 extends through the upper housing wall 108 and in the area of ​​the additional elements, and the load plate 110 can be mounted. In a next step, the additional device, for example, the conveyor belt, can be placed on the load plate and connected to it. The cable 220 can be connected to an electrical device of the additional device, for example, the conveyor belt drive.

[0073] After this assembly process, the mounting element 230 can be pushed into its upper position and locked in place. Finally, the ring element 240 can be moved into its lower position and locked in place. Finally, the cable routed out of the housing 202 of the power transmission device 200 via the housing-fixed cable feedthrough 206 can be connected to the socket device 114. After attaching the housing side wall, the assembly process is complete.

[0074] It should be noted that, of course, one or more steps of the assembly process explained above can also be performed in a different order. For example, the housing 102 can also be designed as a slip-on housing, i.e., the upper housing wall 108 and the side wall 106 are formed as a single piece.

[0075] The modular power transmission device 200 can thus be easily retrofitted to existing force measuring devices with minimal modifications, making the force measuring device in question explosion-proof or contributing to explosion protection. Due to the modular design, one and the same power transmission device 200 can also be used for a wide variety of force measuring device types.

[0076] Finally, it should be noted that, in addition to the low-force shunt electrical connection described above, further electrical or electronic components that are not intrinsically safe can also be arranged in the housing 202, so that the housing 102 of the weighing device 100 no longer contains any critical components that could cause an ignition of an explosive atmosphere within the housing 102.

[0077] The entire power transmission device 200 can also be arranged outside the housing of a force measuring device, for example on the same base frame or connected to the housing of the force measuring device. List of reference symbols

[0078] 100Weighing device 102Housing 104Base plate 106Circumferential side wall 108Upper housing wall 110Load plate 112Labyrinth seal 114Socket device 116Force sensor 118Main body 120Base part 122Load introduction area 124Support plate 126Cable connection 200Power transmission device 202Housing 204Cover cover 206Cable gland 208Connecting part 210Housing-fixed contact device 210aConnecting contact 212Screw 214Access opening 216Connecting element 218Recess 220Cable 222Movable contact device 224Screw 226Contact bridge 228Connecting web 230Mounting element 232Engagement area 234Ring shoulder 236Set screw 238Labyrinth seal 240Ring element 242Recess 244Groove 246Surface Longitudinal axis

Claims

1. Current transmission device for a force measuring apparatus, in particular a weighing apparatus, wherein the force measuring apparatus (100) has a housing (102), and has a base region and a movable region which can be moved relative to one another, (a) comprising a pressure-resistant housing (202) which has a housing wall and can be fixedly connected mechanically to the base region of the force measuring apparatus (100), and comprising a connecting element (216) which, at an outer end region protruding from the pressure-resistant housing (202), can be fixedly connected mechanically to the movable region of the force measuring apparatus (100) in an operating state, (b) wherein the connecting element (216) is designed such that, in the operating state, it passes through the housing wall in a contactless and arc-through-resistant manner, (c) wherein the connecting element (216) is designed as a movable cable passage, wherein a first cable (220), which has at least one electrical line, is guided into the connecting element (216) at the outer end region, passes through the connecting element and is guided into the pressure-resistant housing (202) at an inner end region of the connecting element (216), (d) wherein the pressure-resistant housing (202) comprises a cable bushing (206) which is fixed to the housing and designed for pressure-resistant and arc-through-resistant passage of a second cable, which has at least one electrical line, through the housing wall, (e) wherein a movable contact device (222) is provided on the inner end region of the connecting element (216) and is fixedly connected mechanically thereto, and a contact device (210), which is fixed to the housing, is provided in the pressure-resistant housing (202) and is fixedly connected mechanically to the pressure-resistant housing, wherein at least one flexible electrical contact bridge (226) is formed between the contact device that is movable (222) and the contact device that is fixed to the housing (210), and (f) wherein the at least one line of the first cable is mechanically and electrically connected to the movable contact device (222), and the at least one line of the second cable is mechanically and electrically connected to the stationary contact device (210) such that electrical contact is formed between the at least one line of the first cable and the at least one line of the second cable via the at least one contact bridge (226), and (g) wherein the current transmission device (200) is designed such that it can be mounted in a housing (102) or on the outside of a housing (102) of the force measuring apparatus (100).

2. Current transmission device according to claim 1, characterized in that the connecting element (216) is designed as a substantially cylindrical element and in that the housing wall has a predetermined thickness in a region of a passage opening (214) for the connecting element (216), and the passage opening (214) has a predetermined cross section, which thickness and cross section are selected such that, in the operating state, an arc-through-resistant annular gap is formed between the connecting element (216) and an inner wall of the passage opening (214).

3. Current transmission device according to claim 1 or claim 2, characterized in that the pressure-resistant housing (202) comprises a housing cover (204) which is detachably connected to the pressure-resistant housing and is designed such that the housing cover (204) interacts with an engagement region (204a), which extends into the interior of the housing and has at least one stop shoulder on the outer circumference of the connecting element (216), such that a limit stop is effected with regard to the movement of the connecting element (216), at least with respect to a movement of the connecting element (216) in a movement direction out of the pressure-resistant housing (202).

4. Current transmission device according to claim 3, characterized in that the housing cover (204) comprises (204a) a preferably circumferential flange extending into the pressure-resistant housing (202), which flange forms the engagement region.

5. Current transmission device according to claim 3 or claim 4, characterized in that the at least one stop shoulder is formed by a recess (218) in the outer circumference of the connecting element (216).

6. Current transmission device according to any of claims 2 to 5, characterized in that (a) the passage opening (214) for the connecting element (216), on an outwardly directed region with respect to the pressure-resistant housing (202), is designed as an engagement region (232) for an annular mounting element (230) which encompasses the connecting element (216) and is designed to be movable on said connecting element between an adjustment position and an operating position in the direction of a longitudinal axis (E) of the connecting element (216), the mounting element (230) and the engagement region (232) being designed and, when the mounting element (230) is in the adjustment position, interacting such that the connecting element (216) is positioned in the pressure-resistant housing (202) such that, with the exception of the engagement region (232), the arc-through-resistant annular gap is formed between the connecting element (216) and an inner wall of the passage opening (214), and (b) in that the mounting element (230) releases the connecting element (216) in the operating position.

7. Current transmission device according to claim 6, characterized in that the mounting element (230) is designed to be lockable on the connecting element (216) in the operating position and / or the adjustment position.

8. Current transmission device according to claim 7, characterized in that the mounting element (230) is designed such that it jointly forms a labyrinth seal (238) in the operating position.

9. Current transmission device according to claim 8, characterized in that the mounting element (230) is encompassed by an annular element (240) which can be moved from a mounting position into a working position, the annular element (240), in the working position, being positioned offset in the direction of the pressure-resistant housing (202) with respect to the mounting element (230), and forming the labyrinth seal (238) together with the mounting element (230) and the pressure-resistant housing (202).

10. Current transmission device according to claim 9, characterized in that the pressure-resistant housing (202) comprises a projecting flange (234) surrounding the passage opening (214) to jointly form the labyrinth seal, which flange is preferably encompassed by the annular element (240), an annular gap being formed between an inner wall of the annular element (240) and an outer wall of the flange (234).

11. Current transmission device according to any of the preceding claims, characterized in that the movable contact device (222) and the contact device (210) fixed to the housing are each designed as a printed circuit board.

12. Current transmission device according to claim 11, characterized in that the at least one flexible electrical contact bridge (226) is designed as a flexible electrical conductor, in particular as a metal conductor, for example a gold strip or wire.

13. Current transmission device according to claim 11 or claim 12, characterized in that the printed circuit boards forming the movable contact device (222) and the contact device (210) fixed to the housing are mechanically connected to one another in a mounted state.

14. Current transmission device according to claim 13, characterized in that the printed circuit boards are connected via separating points (228), the printed circuit boards preferably being manufactured together in one piece and the separating points (228) being part of the printed circuit boards.

15. Force measuring apparatus, in particular a weighing apparatus, comprising a current transmission device (200) according to any of the preceding claims.