The present invention relates inter alia to a kneading or mixing machine with a magnetically activatable safety switch arrangement, and with a bowl with a magnet for interaction with the switch arrangement.

GB 2 206 240 discloses a magnetically operated electrical switch comprising a microswitch mounted in a first chamber of a casing. A first magnet is locat- ed adjacent the actuating member of the microswitch and may be urged against the actuating member by magnetic repulsion when a second magnet is moved into proximity therewith by movement of a sliding plunger. The microswitch is mounted in a holder including springs for biasing the first magnet to its non-actuating position, or bias is provided by the microswitch mecha- nism. The second magnet can be biased by magnetic repulsion alone and can be mounted in its own housing. The seal housing may be sealed to the environment. The switch is suitable for installation in bulkheads or the like to serve as a control switch in hostile environments since there is no mechanical linkage between the plunger and microswitch. However, this magnetically operated switch is not suitable as a safety switch for preventing unauthorised operation of for instance a processing apparatus when a high degree of safety is demanded, as the actuation of the microswitch is either depending on a relativly large actuation pressure in order to move the sliding plunger or on the internal bias in the microswitch in order to return the actuating member of the microswitch to its resting position.

CN 202977306 U discloses a magnetically-actuated microswitch comprising a magnetically-actuated microswitch body, wherein the magnetically-actuated microswitch body is provided with a switch button. A magnet pushing device is arranged on the switch button. According to the utility model, by using the magnetically-actuated microswitch, no holes or windows are required on the surface of the product, so that the surface of the product is easy to clean, and water penetration is prevented, thereby ensuring the use safety of the product. However, this magnetically operated switch is not suitable as a safety switch for preventing unauthorised operation of for instance a processing ap- paratus when a high degree of safety is demanded, as the actuation of the microswitch is either depending on a suitably large actuation pressure in order to move the magnet pushing device or on the internal bias in the micro- switch in order to return the switch button of the microswitch to its resting position.

US patent 5877664 describes another magnetically activatable switch operable from a passive state to an activated state by displacing an activation element using an external magnet. The object of the present invention is inter alia to provide a kneading or mixing machine with a magnetically activatable safety switch arrangement providing a high degree of safety.

Summary

In view of this object, a kneading or mixing machine is provided with an electric power safety switch comprising a first and a second standardised miniature snap-action switch arranged next to each other, such as vertically above each other or horizontally next to each other, preferably close to each other, stacked or in mutual abutment, so that their spring-biased actuator buttons are activatable simultaneously by abutment of a first internal permanent magnet, wherein the set of contacts of the first standardised miniature snap- action switch is connected in series functionally with the set of contacts of the second standardised miniature snap-action switch. In this way, with suitably strong first and second internal permanent magnets, it may with a high degree of safety be ensured that the set of contacts is forced to the open state by means of magnetic attraction between the first and second internal permanent magnets as long as no external magnet is within a certain distance of the first internal permanent magnet. Thereby, unauthorised operation of a processing apparatus such as the aforementioned kneading or mixing machine may be ensured with a high degree of safety, as the power supply to the motor may be cut directly or not by the set of contacts being in the open state as long as a certain machine part or element provided with an external magnet is not in its proper position. At the same time an even greater safety may be provided, as failure of one of the standardised miniature snap-action switches will not influence the operation of the magnetically activatable safety switch arrangement, as long as the other switch operates correctly.

By the contacts being "functionally connected in series" is understood herein by way of example a serial coupling or an arrangement including a logic circuit wherein an AND-gate is used, where failure of one of the snap-action switches will not influence the operation of the magnetically activatable safety switch arrangement, as long as the other switch operates correctly.

In an embodiment, the second internal permanent magnet is fixed inside the enclosure and preferably abuts the switch housing of the electric power safety switch. Thereby, the set of contacts may be forced to the open state by means of magnetic attraction between the first and second internal perma- nent magnets in an even more reliable, fast and secure way.

In a structurally particularly advantageous embodiment, the electric power safety switch is a standardised miniature snap-action switch wherein the activation element has the form of a spring-biased actuator button protruding from the switch housing. Preferably, the electric power safety switch is of the type providing forced opening of the set of contacts when a spring-biased actuator button protruding from the switch housing is pressed into the switch housing. Preferably, the electric power safety switch is of the microswitch type.

In an embodiment the electric power safety switch is a normally-closed switch. A normally-closed or NC switch, breaks contact when the spring- biased actuator button is pressed and makes contact when it is released. In an embodiment, the first and second internal permanent magnets have the form of cylindrical magnets arranged so that or substantially so that their cylinder axes run through the spring-biased actuator button. Thereby, the first internal permanent magnet may press on the spring-biased actuator button with its central part and be in a well-balanced orientation, thereby being able to slide smoothly in a section of an enclosure having a cylindrical cavity or bore.

In a structurally particularly advantageous embodiment, the first internal permanent magnet is guided displaceably inside a section of the enclosure hav- ing a cylindrical cavity, the cylindrical cavity has a first end open to the switch housing of the electric power safety switch or closed by a first end cap opposing the switch housing, and the cylindrical cavity has a second end closed by a second end cap. Preferably, the second end cap is made from a resilient material, such as silicone. Thereby, a smoother operation of the magnetically activatable safety switch arrangement may be ensured.

In an embodiment, the first internal permanent magnet is guided displaceably inside a section of the enclosure having a cylindrical cavity, wherein the cylindrical cavity has a first end open to the switch housing of the electric power safety switch or closed by a first end cap opposing the switch housing or somewhat closed by the enclosure so that at least the activation element can extend into the cylindrical cavity, and the cylindrical cavity has a second end closed by the enclosure.

In an embodiment the external magnet is positioned in a certain distance from the first internal permanent magnet so that the force of attraction between the external magnet and the first internal permanent magnet becomes stronger than the force of attraction between the first and second internal permanent magnets.

The first and second internal permanent magnet as well as the external magnet may all have the same attraction force or the first and second internal permanent magnet as well as the external magnet may each have an attrac- tion force different from one or two of the other two magnets so that the distance between the external magnet and the first internal permanent magnet and/or between the first and second internal permanent magnet can be varied. The present invention further relates to a processing machine, such as a kneading or mixing machine, having a machine housing including a magnetically activatable safety switch arrangement as described above, wherein the processing machine is adapted to carry a processing tool, such as a kneading or mixing tool, driven by a motor, wherein the processing machine in- eludes a safety shield adapted to at least partly shield the processing tool in relation to a user when the safety shield is in a shielding position in relation to the processing tool, the safety shield being arranged displaceably away from its shielding position in order to allow access to the processing tool, wherein the motor is powered directly or not, through the set of contacts of the electric power safety switch, and wherein the external magnet is arranged in the safety shield. In an embodiment, this processing machine is provided with four magnetically activatable safety switch arrangements, wherein the safety shield has a ring-formed contact element adapted to abut a first stationary surface of the machine housing of the processing machine, said surface extending at least substantially about a rotational axis of the processing tool, wherein the safety shield is composed by two separate shield sections each including a respective part of the ring-formed contact element, so that each of the shield sections may be mounted before the other shield section is mounted, wherein each respective part of the ring-formed contact element pertaining to a respective shield section is provided with two spaced apart external magnets each adapted for interaction with a respective first internal permanent magnet pertaining to a respective one of the four magnetically activatable safety switch arrangements. Thereby, it may be ensured that the motor of the pro- cessing machine is stopped even if a user tilts only one of the shield sections slightly, as at least one of the four magnetically activatable safety switch arrangements may be activated. It is noted that the arrangement of four magnetically activatable safety switch arrangements as described above is a separate invention and that the function and inventive idea of this invention is independent of the type of the magnetically activatable safety switch arrangements used. That means that the magnetically activatable safety switch arrangements used in said separate invention may be of a different type than that described above. Said separate invention may in particular be protected by means of a divisional patent application.

In another aspect of the invention a magnetically activatable safety switch arrangement includes an enclosure comprising a switch housing cavity wherein an electric power safety switch can be arranged, a first internal permanent magnet arranged displaceably in the enclosure adjacent to the switch housing cavity and a second internal permanent magnet arranged inside the enclosure oriented so that the first and second internal permanent magnets attract each other and so that the first internal permanent magnet is displaced toward the switch housing cavity.

In this aspect of the invention the electric power safety switch comprises an activation element which is maintained in its activated position by the first internal permanent magnet due to the attraction force between the first and second internal permanent magnets when the electric power safety switch is arranged in the switch housing cavity in the enclosure. This as the electric power safety switch further includes a switch housing with a set of contacts and the activation element, wherein the electric power safety switch is operable from a passive state to an activated state by displacing the activation element from a rest position to an activated position, wherein the activation element is biased towards its rest position, wherein in the passive state of the electric power safety switch, the set of contacts is in a closed state, and in that, in the activated state of the electric power safety switch, the set of contacts is in an open state.

Brief description of the drawings Fig. 1 A is a cross-sectional view through a first embodiment of a magnetically activatable safety switch arrangement, where the electric power safety switch is in an active and open state.

Fig. 1 B is a cross-sectional view through the first embodiment of Fig. 1 A of a magnetically activatable safety switch arrangement, where the electric power safety switch is in a passive and closed state.

Fig. 2A is a cross-sectional view through a second embodiment of a magnetically activatable safety switch arrangement, where the electric power safety switch is in an active and open state. Fig. 2B is a cross-sectional view through the second embodiment of Fig. 2A of a magnetically activatable safety switch arrangement, where the electric power safety switch is in a passive and closed state. Fig. 3 shows a first implementation of a set of magnetically activatable safety switch arrangements in a processing machine in connection with shield detection.

Fig. 4a-4d shows a second implementation of a set of magnetically activata- ble safety switch arrangements in a kneading or mixing machine in connection with bowl detection, fig. 4b-d being detailed views of a section identified by letter A in fig. 4a, and representing a vertical cross-sectional view and horizontal cross-sectional views along line B-B in fig. 4a. Fig. 5a-5b show a switch arrangement with a first and second standardised miniature snap-action switch, with the enclosure open and closed, respectively.

Detailed description

The invention will now be explained in more detail below by means of examples of embodiments with reference to the schematic drawings, in which Fig. 1A shows a first embodiment of a magnetically activatable safety switch arrangement 1 including an enclosure 2 and an electric power safety switch 3 arranged at least partially inside the enclosure 2. The enclosure 2 may be manufactured as one part and may, or may not, be totally enclosed. The enclosure 2 may be made from any material. The material may be suitable for moulding. The material may preferably be a non-magnetic material such as Acrylonitrile butadiene styrene (ABS) and Polyoxymethylene (POM). The electric power safety switch 3 includes a switch housing 4 with a set of contacts (not shown) and an activation element 5 such as a spring-biased actua- tor button 5 (see Fig. 1 B) and is operable from a passive state to an activated state by displacing the activation element 5 from a rest position to an active position. When no activation force from the first internal permanent magnet 6 influences the activation element 5, the activation element 5 is biased to- wards its rest position as shown in Fig. 1 B. The activation force may be any force suitable for activating the activation element 5. A first internal permanent magnet 6 and a second internal permanent magnet 7 are likewise arranged inside the enclosure 2 on each side of the electric power safety switch 3. The first internal permanent magnet 6 is arranged in a section of the enclosure 2 having a cavity 9 or bore allowing the first internal permanent magnet 6 to move from one end of the cavity 9 to the other end of the cavity 9. Said section of the enclosure 2 may be formed as a cylindrical part of the enclosure 2. The cavity 9 has a first end 10 open to the switch housing 4 of the electric power safety switch 3, closed by a first end cap (not shown) opposing the switch housing 4 or somewhat closed by the enclosure 2 so that at least the activation element 5 can extend into the cavity 9, and the cavity 9 has a second end 1 1 closed by a second end cap 12. The second end cap 12 is pref- erably made from a resilient material, such as silicone. One or both of the first and second internal permanent magnets 6, 7 may be shaped like a cylinder. If the first internal permanent magnet 6 is cylindrical, the shape of the cavity 9 may likewise be cylindrical so that the first internal permanent magnet 6 is displaceably guided in the cavity 9. The activation element 5 on the electric power safety switch 3 extends through the first end 10 of the cavity 9 and through a potential first end cap (not shown) into the cavity 9. The cavity 9 may also be frustoconical from the first end 10 to the second end 1 1 .

The first and second internal permanent magnets 6, 7 are oriented so that they attract each other and so that they displace the activation element 5 into an active and open position. Fig. 1A thereby shows the electric power safety switch 3 in an active state.

Fig. 1 B shows the first embodiment of the magnetically activatable safety switch arrangement 1 , where the electric power safety switch 3 is in a passive state. This is obtained by positioning an external magnet 8 a certain distance from the first internal permanent magnet 6 so that the force of attraction between the external magnet 8 and the first internal permanent magnet 6 becomes stronger than the force of attraction between the first and second internal permanent magnets 6, 7. The first internal permanent magnet 6 is hereby displaced within the cavity 9 towards the external magnet 8 and reloads the activation element 5. As no activation force influences the activation element 5, the activation element 5 is biased towards its rest position. Fig. 2A shows a second embodiment of a magnetically activatable safety switch arrangement 1 including an enclosure 2 and two electric power safety switches 3 arranged at least partially inside the enclosure 2. The enclosure 2 may be composed by two separate parts which can be assembled by means of fastening means such as threated means, e.g. screws, or snap-fit connec- tions or they may be glued together etc. The enclosure 2 may, or may not, be totally enclosed. The enclosure 2 may be made from any material. The material may be suitable for moulding. The material may preferably be a nonmagnetic material such as Acrylonitrile butadiene styrene (ABS) and Polyox- ymethylene (POM). Each electric power safety switch 3 includes a switch housing 4 with a set of contacts (not shown) and an activation element 5 such as a spring-biased actuator 5 (see Fig. 2B) and is operable from a passive state to an activated state by displacing the activation element 5 from a rest position to an active position. When no activation force from the first internal permanent magnet 6 influences the activation element 5, the activation element 5 is biased towards its rest position as shown in Fig. 2B. The activation force may be any force suitable for activating the activation element 5. The two electrical power safety switches 3 are preferably placed next to each other so that the two activation elements 5 are closed to each other. A first internal permanent magnet 6 and a second internal permanent magnet 7 are likewise arranged inside the enclosure 2 on each side of the electric power safety switches 3. The first internal permanent magnet 6 is arranged in a section of the enclosure 2 having a cavity 9 or bore allowing the first internal permanent magnet 6 to move from one end of the cavity 9 to the other end of the cavity 9. The cavity 9 has a first end 10 open to the switch housing 4 of the electric power safety switch 3, closed by a first end cap (not shown) opposing the switch housing 4 or somewhat closed by the enclosure 2 so that at least the activation element 5 can extend into the cavity 9. One or both of the first and second internal permanent magnets 6, 7 may be shaped like a cylinder. If the first internal permanent magnet 6 is cylindrical, the shape of the cavity 9 may likewise be cylindrical so that the first internal permanent magnet 6 is dis- placeably guided in the cavity 9. The activation element 5 on the electric power safety switch 3 extends through the first end 10 of the cavity 9 and through a potential first end cap (not shown) into the cavity 9.

The first and second internal permanent magnets 6, 7 are oriented so that they attract each other and so that they displace both activation elements 5 into an active and open position. Fig. 2A thereby shows the electric power safety switch 3 in an active state.

Fig. 3 shows a first implementation of a set of magnetically activatable safety switch arrangements 1 in a processing machine 100 in connection with shield detection. The processing machine 100 may be a kneading or mixing machine having a machine housing 101 adapted to carry a processing tool (not shown), such as a kneading or mixing tool driven by a motor (not shown). The machine housing 101 also have a first stationary surface 104 adapted to carry a safety shield 102. The first stationary surface 104 may be approximately horizontal. The safety shield 102 includes a ring-formed contact element 103 which is configured for being mounted on the first stationary surface 104.

Preferably four magnetically activatable safety switch arrangements 1 as described above may be included in the machine housing 101 close to the first stationary surface 104 and positioned so that the first internal permanent magnet 6 (see Fig. 1A-B and 2A-B) is closer to the first stationary surface 104 than the second internal permanent magnet 7 (see Fig. 1A-B and 2A-B).

The ring-formed contact element 103 on the safety shield 102 is provided with four spaced apart external magnets 8 (see Fig. 1A-B and 2A-B) each adapted for interaction with a respective first internal permanent magnet 6 (see Fig. 1A-B and 2A-B) pertaining to a respective one of the four magnetically activatable safety switch arrangements 1 included in the machine housing 101 .

The motor for running the processing tools is powered directly or not through a set of contacts of the electric power safety switches 3 (see Fig. 1A-B and 2A-B) in the four magnetically activatable safety switch arrangements 1 when all the electric power safety switches 3 is in a passive state. All the electric power safety switches 3 is in a passive state when the ring-formed contact element 103 on the safety shield 102 is correctly mounted to the first station- ary surface 104 on the machine housing 101 .

The safety shield 102 may be composed by two separate shield sections 105 each including a respective part of the ring-formed contact element 103, wherein each respective part of the ring-formed contact element 103 pertain- ing to a respective shield section 105 is provided with two spaced apart external magnets each adapted for interaction with a respective first internal permanent magnet 6 (see Fig. 1A-B and 2A-B) pertaining to a respective one of the four magnetically activatable safety switch arrangements 1 .

Fig. 4a shows a second implementation of a set of magnetically activatable safety switch arrangements 1 in a processing machine 100 in connection with bowl detection. The processing machine 100 here is a kneading or mixing machine having a machine housing 101 adapted to carry a processing tool T (not shown in details) in the form of a kneading or mixing tool driven by a motor (not shown). The machine housing 101 also includes a bowl retainer 107 which is attached to the interior of the machine housing 101 through a second stationary surface 108 on the machine housing 101 and adapted to fixate and carry a stainless steel bowl 106 with a cylindrical upper wall portion by the bowl retainer 107 having two opposite projecting portions, of which one is shown in fig. 4a, which portions extending along a respective side portion of the bowl 106. The second stationary surface 108 may be approximately vertical. The bowl retainer 107 can be displaced vertically between an upper position and a lower position by means of a handle 109. When the bowl retainer 107 is in the lower position each projection of the bowl retainer 107 is level with a receiving recess mounted to the outside of opposite surface por- tions of the bowl 106, the bowl 106 supported by the illustrated wheeled trolley being properly oriented such that the receiving recesses are aligned to receive a respective projection on the bowl retainer 107. Raising the bowl 106 from the lower position by manipulating the handle 109 moves a magnet 8 fixed to the bowl 106 in a plane of symmetry of the bowl 106 between the receiving recesses, closer to the tool T.

A magnetically activatable safety switch arrangements 1 as described above is included in the machine housing 101 close to the second stationary surface 108 of the machine housing 101 and positioned so that the first internal permanent magnet 6 is closer to the second stationary surface 108 than the second internal permanent magnet 7. The enclosure 2 includes two vertically stacked snap-action switches 3, 3', as seen best in fig. 4b.

As mentioned, the bowl 106 is provided with an external magnet 8 adapted for interaction with the first magnet 6 (see Fig. 1A-B and) 2A-B of a safety switch arrangement 1 , or with several external magnets 8 for interaction with a respective first internal permanent magnets 6 (see Fig. 1A-B and 2A-B) pertaining respective magnetically activatable safety switch arrangements 1 included in the machine housing 101 . The bowl retainer 107 may comprise a guiding means 1 10 such as a hole in order to guide the placement of the bowl 106 so that the interaction between the external magnet 8 and the first permanent magnet 6 in the magnetically activatable safety switch arrangement 1 is optimal. The motor for running the processing tools is powered through a set of contacts of the electric power safety switches 3 (see Fig. 1 A- B and 2A-B) in the magnetically activatable safety switch arrangement 1 when the electric power safety switch 3 is in a passive state. The electric power safety switch 3 is in a passive state when the bowl 106 is correctly placed and fixated in the bowl retainer 107 and when the bowl retainer 107 is in the upper position, as shown in fig. 4a, 4b and 4c. Fig. 4d shows the switch arrangement 1 when no bowl 106 is present. As will be understood, in the aforementioned embodiment the magnet 8 on the bowl 106 is not purposely used to indicate correct positioning of the bowl 106 when supported by the bowl retainer 107 but to control operation of the motor, although such an indication may of correct positioning may be implicit.

Fig. 5a and 5b show the enclosure 2 with two switches 3, 3' and magnets 6, 7, which enclosure 2 preferably is a two-part assembly which is preassem- bled as shown in fig. 5b, for mounting in the machine housing 101 .