This invention relates to interlock systems, and it relates especially, though not exclusively, to such systems as are intended for use as safety measures in domestic electrical appliances, such as food processors, food mixers, blenders and the like; in general any appliance that has moving parts and/or heating elements that could, under certain operational circumstances, cause harm to a user in the absence of the interlock system. The invention also encompasses a domestic electrical appliance incorporating such an interlock system.

Interlock systems are an essential feature of many domestic appliances, and their components need to satisfy demanding, and sometimes opposing, operational, regulatory, economic and aesthetic criteria. Hence difficulties arise in providing interlock systems that are sufficiently robust and reliable to meet user demands and comply with stringent regulatory stipulations, whilst being economical to produce and conforming to an acceptable aesthetic design.

Many interlock systems have been devised hitherto for sensing when safe and unsafe conditions obtain in domestic electrical food preparation equipment and the like. A typical condition required to be sensed with such equipment is the presence or absence of a lid or cover on a receptacle within which a processing tool is to be rotated or otherwise moved by means of an electric motor. Typically, such tools, are driven at relatively high speeds and contain sharply edged blades or rasp-like features which are intended to cut, mash or otherwise comminute food

items placed in the receptacle for processing. Accordingly, dangerous situations can arise if such tools are operated whilst the receptacle is open, and thus it is standard practice to provide the lid or cover with some kind of actuator which operates, directly or indirectly, on an interlock switch means, such that the supply of electrical current to the motor is interrupted unless the lid or cover is securely in place upon the receptacle.

It will be appreciated that, where the aforementioned actuator associated with the lid or cover operates directly upon the interlock switch means, it is necessary either to dispose the switch means near the lid or cover or to have the actuator carry a significant extension piece that can reach a more remotely-located switch means. For various reasons, neither configuration is particularly attractive for practical use, and thus the majority of equipment utilises indirect operation.

Indirect operation implies that the actuator associated with the lid or cover operates an intermediate member which then, in turn, operates the switch means. Again, many different types of intermediate member have been tried, such as levers, push-rods and the like; though difficulties remain in providing a system which can accurately and reliably convey the status of the actuator to the switch means by way of a mechanism which is rugged, reliable, cost- effective, resistive to (or insensitive to) the ingress of food or other products processed by the equipment, aesthetically acceptable and which cannot readily be compromised (accidentally or deliberately) by users.

It is an object of this invention to address such difficulties and, in accordance with one example of the invention there is provided an interlock system for actuating a switch means configured to normally interrupt a flow of electrical current to a component of a domestic electrical appliance when a first predetermined condition, prescribed as unsafe, obtains; the system comprising a rod-like member, means for sensing the occurrence of a second predetermined condition wherein said unsafe condition no longer obtains, and for responding to the sensing of said second predetermined condition by turning the rod-like member about its own axis; and means for actuating said switch means, when the rod-like member is turned through at least a predetermined angle, to permit said electrical current to flow.

In one preferred embodiment of the invention, the said appliance incorporates a receptacle with which said interlock system is associated; the first predetermined condition comprises the absence of a lid or cover from said receptacle and the second predetermined condition comprises the secure placement of the lid or cover on said receptacle in a manner intended for operation of the appliance.

The lid or cover is preferably provided with an engagement member which adopts a predetermined position relative to the receptacle when the lid or cover is securely placed thereon. In such circumstances, in one preferred embodiment of the invention, the means for sensing the occurrence of said second predetermined condition comprises a cam member carried by said rod-like member and responsive to sliding contact with said engagement member to rotate said rod.

In an alternative embodiment, the means for sensing the occurrence of said second predetermined condition comprises a gear wheel carried by said rod-like member and responsive to engagement with said engagement means to rotate the rod-like member.

It is further preferred that the said component of the appliance comprises an electric motor adapted to drive in rotation a mobile tool, disposed within said receptacle, in order to comminute or otherwise act upon foodstuffs or other produce placed therein.

Typically, the lid or cover for the receptacle is formed with an upstanding, chimney-like feed-tube through which food items can be added for processing in the receptacle. A "pusher", typically of plastics material and sized to fit closely within the feed tube, is further provided, by means of which a user can urge foodstuffs down into the receptacle for processing. Such feed tubes provide direct access to the interior of the receptacle and thus, in principle, can compromise operational safety. Many such tubes, however, are dimensionally configured to be relatively narrow in breadth and relatively tall in height, so that any such compromise is minimal.

There is, however, a demand for food preparation equipment provided with a wide feed-tube and associated pusher, to enable relatively bulky food items to be added to the receptacle for processing. Such equipment presents special difficulties as regards the interlock requirements, since there is now a need to detect not only that the lid or cover is in place, but

also that a pusher has been inserted into the feed tube, before the motor can be driven. Thus, a dual interlock system is required.

The invention has particularly beneficial application to equipment having such wide feed-tubes and accordingly, in another preferred embodiment of the invention, there is provided a dual interlock system for a domestic electrical appliance provided with a receptacle containing a tool for comminuting or otherwise acting upon foodstuffs therein, said receptacle being intended to be closed when said tool is operative therein by a lid or cover bearing a relatively wide feed-tube; the interlock system including a switch means configured to normally interrupt a flow of electrical current to a motor for rotating said tool, means to sense when the lid or cover is in place on said receptacle and a pusher device is located within said feed-tube; the system comprising a rod-like member, means for sensing the placement of said pusher device in said feed-tube, and for responding to the sensing of said placement by turning the rod-like member about its own axis; and means for actuating said switch means, when the rod-like member is turned through at least a predetermined angle, to permit said electrical current to flow.

In order that the invention may be clearly understood and readily carried into effect, certain embodiments thereof will now be described with reference to the accompanying drawings, of which:

Figure 1 shows, in side elevation and in part cross-sectional view, a food processor in accordance with one example of the invention;

Figure 2(a) shows, in schematic and perspective view, certain operational elements of a system, in accordance with one example of the invention, that is usable with the food processor of Figure 1; and

Figure 2(b) shows, in schematic and perspective view, certain operational elements of a system, in accordance with another example of the invention, that is usable with the food processor of Figure 1.

Typically, prior art interlock systems capable of preventing operation of a domestic food mixing or processing appliance until a lid or cover has been properly located on an otherwise open receptacle in which a processing tool is driven to process foodstuffs, use a push-rod which runs down a side-wall of the receptacle. Usually the upper end of the push- rod is disposed within a shrouded location atop the side-wall, and its lower end protrudes through a small aperture into a base casing which supports the receptacle in use and which also houses a drive motor for the appliance. In such systems, a normally open cut-off switch, or an actuator for such a switch, is also disposed within the housing and close to the aperture. The rod is spring-loaded away from the cut-off switch or its actuator. In use, when the lid or cover is rotated to set it in its correct operative position upon the receptacle, an actuator formed on the rim of the lid or cover enters (through a suitably located slot) the shroud that covers the upper end of the rod and engages the upper end of the rod with a camming action, so as to force it downwards, against the spring pressure, such that the lower end of the rod impacts the cut-off switch or its actuator, thereby closing the switch and permitting electrical current to flow to the motor.

This is an effective and reliable interlock system, and the embodiment of the invention now to be described utilises such a system as one component of a dual interlock system.

Accordingly, and with reference to Figures 1 and 2(a), a first embodiment of the invention comprises a dual interlock system in which a domestic electrical appliance 1, in this example, a food processor, comprises a base casing 2 which houses an electric motor 3 and various electrical connections thereto including an energising connection 4, which may (depending on the type and rating of the motor 3) be connected directly to a mains lead 5 or alternatively to a source, such as a transformer, of a different voltage; the source in that case being connected to the mains lead.

The energising connection 4 is coupled to the motor by way of a normally open cut-off switch 6 which is located, in this example, close to an aperture 7 in the upper surface 8 of the casing 2. The upper surface 8 of the casing 2 is also intended to support and locate a receptacle 9, such as a food-processing bowl, in which a mixing, cutting or other form of processing tool can be mounted for rotation by the motor 3. The upper surface 8 is further apertured at 10 to permit drive to be transmitted from the motor 3 to the tool in the bowl 9, as is well known in the art.

The bowl 9 is provided with a lid or cover 11 which needs to be properly located upon the upper rim of the bowl 9, thereby preventing a user from accessing the interior of the bowl, before the motor can be permitted to

operate. Accordingly, a first interlock system is provided whereby a rod 12 is mounted for vertical movement relative to the side-wall of the bowl 9; the lower end of the rod 12 being positioned, when the bowl 9 is properly located on the upper surface 8 of the casing 2, directly above the aperture 7 in the surface 8. The upper end of the rod is shrouded, to prevent users from directly pressing it, and the rod 12 is spring-loaded to cause the upper end thereof to remain within the shroud unless physically pressed downwards, against the spring pressure, as will now be described.

When the lid 11 is properly located on the upper rim of the bowl 9, a flange 13 formed on the edge of the lid 11 enters the shroud and contacts the upper end of the rod 12. The inter-engaging surfaces of the flange 13 and the upper end of rod 12 are formed with respective cam profiles that are such as to cause the flange to depress the rod 12, against the aforementioned spring pressure, thus causing the lower end of the rod to enter the casing 2 via aperture 7 and to push the actuator of the cut-off switch 6, thereby closing the switch contacts and enabling the supply of electricity to the motor by way of connection 4.

The lid or cover 11, however, carries a wide feed-tube 14, and thus could compromise the safety provided by the interlock system described thus far unless further safety provision is made. In accordance with this embodiment of the invention, the further safety provision is provided by means of a second interlock system which is sensitive to the placement of a pusher device 15 of the correct dimensions within the feed-tube 14.

The dual system in this embodiment comprises a further, vertically- disposed rod 16, which is housed at an edge of the feed-tube 14; the upper end of the rod being encased within a protective housing 17 intended to prevent deliberate or accidental frustration of the dual interlock.

The upper edge of the pusher 15 (that which is pressed by the user) is formed with a downwardly-dependent prong member 18 which is shaped to engage with a cam 19 formed at the top of the rod 16; the arrangement being such that, when the pusher device 15 is located correctly in the mouth of the wide feed-tube 14, the prong 18 enters the protective housing 17 and, as the pusher device 15 is pressed further into the feed- tube, the prong 18 bears against the cam 19, causing the rod 16 to rotate about its own axis thereby to introduce a lower cam member 20 into a slot in the shroud on the wall of bowl 9, thereby to depress the rod 12 in a manner analogous to that described above.

The rod 16 is spring-loaded in torsion to hold the lower cam member 20 out of contact with the rod 12 until the rod 16 has been rotated as described by interaction with the prong 17.

Thus it will be appreciated that, if a lid or cover 11 carrying a conventional, narrow feed-tube is used, the interlock system device acts conventionally by depression of the rod 12. If, on the other hand, a lid or cover carrying a wide feed-tube is employed, the interlock system requires the dual interaction of the rods 12 and 16 as described.

In an alternative arrangement, a narrow feed-tube may be provided for insertion into a wide feed-tube for use in circumstances where the wide feed-tube is not necessary.

It will be appreciated that, in the embodiment described above, the shroud on the bowl may be provided with two entry slots; one associated with a flange on a lid or cover carrying a conventional, narrow feed-tube, and the other associated with the cam that is urged into it by means of the rotating rod 16. Alternatively, the flange and the cam may both access the shroud via a common slot. Alternatively or in addition, the flange carried by the lid or cover may be used to prime the rod 12 for actuation by the rod 16 when the pusher is introduced into the aforementioned wide feed-tube. Still further, the flange carried by the lid or cover bearing a wide feed-tube might be shaped and configured to operate upon the shroud, rather than the rod 12; the arrangement being such that entry of the flange into the shroud from one direction opens a window or cover over a slot for entry of the actuator attached to rod 16 from the opposing direction.

Driving the rod 16 in rotation, rather than merely depressing it, provides considerable advantage in terms of operational reliability and simplicity of construction. Being rotated around its own axis, the rod 16 tends to self-clean the structure in which it is supported, and the degree of rotation, and hence operational freedom, is readily controllable by suitably shaping the interacting cam surfaces and/or by providing a screw-threaded bearing in which the rod can be turned.

In an alternative embodiment, the cam mechanism for driving the rod 16 in rotation may be replaced by a mechanism such as that used for retractable pen bodies, whereby a downward motion of an actuator generates a rotating motion of a tubular or rod-like member.

In further alternative embodiments, usable in both single and dual interlock systems, and as shown by way of example in Figure 2(b), the rod 12 can also be configured to rotate about its own axis and thereby be actuated in any of the ways described in relation to rod 16. Moreover, in a dual system, if the rod 16 is also caused to rotate about its own axis, rather than being merely pushed, the co-operation between the rods 12 and 16 can be effected by disposing the rods directly in line with one another and having the upper rod 16 screw onto a fixing at the top of rod 12, thereby to rotate the latter for downward motion.