Electrical appliance with adapter seatable upon a base unit
BACKGROUND OF THE INVENTION 
     The invention relates to elecrical appliances, such as household or industrial appliances. 
     More particularly, the invention relates to the powering of such appliances. 
     Conventionally, the appliances used in a particular household or industrial installation are each provided with their own connecting cords, for example cords provided with plugs which can be inserted into wall sockets, or the like. Generally, the appliances, whether household or industrial, are also provided with grounding lines and grounding contacts which must be properly connected to grounding terminals in the household or plant. Examples of household appliances of the type in question would include coffee grinders, mixers, meat grinders, kitchen machines, fruit pressers, and so forth. 
     SUMMARY OF THE INVENTION 
     It is a general object of the invention to provide a plurality of such electrical appliances with a common base unit. The base unit will be provided with a cord which can be plugged into a wall socket, or otherwise connected to a suitable power supply. The individual appliances, however, will be cordless and can be powered by merely placing them on the base unit in a proper position. 
     This object, and others which will become more understandable from the description, below, of preferred embodiments can be met, according to one advantageous concept of the invention, by providing in combination a cordless electrical appliance, an adapter unit for the appliance, and a base unit. The adapter unit is either permanently or removably attached to the appliance. The base unit is provided with supply-voltage-connection contacts for connection to a supply voltage, and with two appliance-current-path contacts. The base unit contains an appliance-current path connected between the supply-voltage-connection contacts and the appliance-current-path contacts. The base unit also contains a step-down transformer having a primary winding connected across the supply-voltage-connection contacts and having a secondary winding. The base unit includes an auxiliary current path connected across the secondary winding, and is provided with two auxiliary-current-path contacts connected in the auxiliary current path and serving to close the auxiliary current path when electrically connected together. Connected in the auxiliary current path is a relay winding controlling the operation of a relay switch connected in the appliance-current path, the relay winding closing the relay switch when the auxiliary current path is closed. The base unit also contains grounding means for connection to ground. The adapter unit is provided with two appliance-current-path contacts electrically connected to the internal circuitry of the electrical appliance, and with connecting means for connecting together the two auxiliary-current-path contacts of the base unit. Also, the adapter unit is provided with grounding means for grounding the appliance. The base unit and adapter unit are so configured, and the contacts and grounding means of the base unit, and the contacts, grounding means and connecting means of the adapter unit are so located on the base unit and the adapter unit, respectively, that when the adapter unit is placed upon the base unit in a single predetermined position, the appliance-current-path contacts of the adapter unit engage those of the base unit, the connecting means of the adapter unit electrically connects together the auxiliary-current-path contacts of the base unit, and the grounding means of the adapter unit becomes electrically connected to the grounding means of the base unit. 
     According to another advantageous concept of the invention, the grounding means of the adapter unit is electrically connected to the connecting means of the adapter unit, and the grounding means of the base unit is electrically connected to one of the two auxiliary-current-path contacts of the base unit. This makes for a high degree of safety and reliability with respect to proper grounding of the electrical appliance. The appliance-current-path within the base unit cannot be closed until the relay switch therein closes. The relay switch does not close until the relay winding in the auxiliary current path is energized. The auxiliary current path cannot be closed until the auxiliary-current-path contacts on the base unit are connected together. Thus, the closing of the appliance-current path necessarily occurs only when the grounding means of the adapter unit and the grounding means of the base unit have become electrically connected to each other. Likewise, if as a result of dirtying of contacts, the establishment of proper grounding is prevented, then necessarily the closing of the appliance-current path is likewise prevented. 
     The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 depicts the circuitry of one embodiment of the invention; 
     FIG. 2 depicts the circuitry of another embodiment of the invention; 
     FIG. 3 is a vertical section through an adapter unit, partially illustrating also the electrical appliance to which the adapter unit is attached, the adapter unit being shown as it is being lowered into proper position on the base unit; 
     FIG. 4 is a view corresponding to FIG. 3, but with the adapter unit seated upon the base unit; 
     FIG. 5 is a top view of the adapter unit; and 
     FIG. 6 is a bottom view of the adapter unit. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 depicts the circuitry employed in one exemplary embodiment of the invention. A household appliance 1, here a flat iron shown in broken lines standing upon its end, or alternatively a coffee maker, or the like, comprises an internal heating resistor 2 and internal electrical connections. The appliance 1 additionally includes a thermostatic temperature regulator 3, a non-illustrated indicator lamp, and the like. The appliance 1 is provided with two fixedly located electrodes 6 and 7; these may be electrical contacts, plugs or sockets. Electrodes 6 and 7 are internally connected, by means of leads 4, 5 with the thermostatic regulator 3 and the heating resistor 4. Contacts 6, 7 are located within an adapter, described further below. The adapter is permanently attached to the appliance or, preferably, removably attached thereto and interchangeable as between a plurality of appliances. The adapter is provided with a metal plate 40 which, in a manner described below, serves to bridge two electrical contacts and thereby close an auxiliary circuit for energizing a relay device located within the base unit 8, when the appliance, with the adapter attached thereto, is placed upon the base unit 8, properly positioned relative thereto. 
     In FIG. 1, the circuitry contained within the base unit 8 is enclosed by dash-dot lines. The base unit 8 is provided at its upper end with two insulated fixedly located contacts 9, 10. These are connected, via electrical lines 11, 11a and 12, 12a to the household power supply, or more particularly to the connecting terminals 15, 16 which are connected to the household power supply. Connected in each of these two connecting lines is a respective one of two normally open relay switches 13, 14, cooperating with relay windings 23, 24. Alternatively, use could be made of a single relay winding cooperating with two normally open relay switches; this latter possibility is discussed with respect to FIG. 2. When the appliance 1 is removed from the base unit 8, the normally open switches 13, 14 are open, so that contacts 9, 10 will be unable to conduct current. 
     The base unit 8 additionally is provided with contacts 17, 18 across which a potential difference is established when the base unit is connected to the houshold power supply, e.g., by being plugged into a wall socket. Preferably, this potential difference is selected to be 24 volts. For reasons of safety, it is preferable that this voltage be a D.C. voltage. To this end, contact 17 is connected via a line 19 to an output terminal of a rectifier 21 which, in turn, is connected across the secondary winding 26 of a transformer. The other contact 18 is connected via an electrical line 20 to the relay winding of the base unit, and in the embodiment of FIG. 1 is connected via electrical lines 20, 20a to the respective relay windings 23, 24. Relay windings 23, 24 are connected via lines 22, 22a to the other output terminal of rectifier 21. The primary winding 25 of the transformer is connected across the household voltage, in particular across the connecting terminals 15, 16 of the base unit, and here is connected in parallel to the current path of the heating coil 2 referred to above. 
     As indicated in FIG. 1, only when metal plate 40 bridges electrical contacts 17, 18 is voltage applied across the relay windings 23, 24, whereupon the cooperating normally open relay switches 13, 14 close, so that the household voltage will become applied across contacts 9 and 10, for example a household voltage of 220 volts A.C. When the appliance 1 with its adapter attached thereto is placed upon the base unit 8, the metal plate 40 bridges contacts 17, 18, and the insulted electrodes 6, 7 engage the insultated electrodes 9, 10. As a result, the heating operation is automatically performed. When the appliance is then lifted off the base unit 8, the relay windings 23, 24 become automatically deenergized, and the normally open switches 13, 14 reassume their open settings. 
     As indicated in FIG. 1, a safety contact line 27 is connected between the electric appliance 1 and the metal plate 40. A further safety contact line or grounding line 28 is connected to the line 19 between the rectifier stage 21 and the contact 17 of the auxiliary current path. These interconnections provide the advantage that a grounding of the electric appliance is always assured whenever the contacts 17, 18 are bridged by the metal plate 40 as a result of resting the appliance with its adapter upon the base unit and voltage is applied across the relay windings. The relay windings then close their associated switches and the actual main current path of the electric appliance can be closed. 
     FIG. 2 depicts the circuitry of another exemplary embodiment of the invention, corresponding to a great extent to that of FIG. 1, with corresponding circuit components being denoted by the same reference numerals as employed in FIG. 1. In FIG. 2, instead of the two relay windings 23, 24 of FIG. 1, only a single relay winding 23 is provided, operative for controlling the settings of both contacts 13, 14 of the main current path of the appliance. Furthermore, instead of the rectifier stage 21 of FIG. 1, use is made of a diode 41, or of another suitable semiconductor element. Also, a capacitor 42 is connected in parallel across the secondary winding 26 of the transformer. 
     FIG. 3 is a vertical section through an exemplary embodiment of the adapter shown being lowered towards its proper position of rest upon the base unit. An electric appliance 120 is provided, in conventional manner, with internal contacts 130 for operating current and with a grounding contact line 140, as well as with electrical connecting leads 110. The adapter 100 is comprised of an outer wall 80 and a middle separating wall 200. The adapter is so designed as to correspond to the positive shape and the recess 150 of the base unit 270, the recess 150 being bounded by an upwardly projecting rim 270a. 
     When the adapter is stood upon the base unit, it can assume only one positive position. The separating wall 200 subdivides the interior of the adapter 100 into an upper chamber 70 and a lower chamber 300. In the lower chamber 300 there are located the electrodes 101 which carry the household current. These are so mounted that, when the adapter 100 is rested upon the base unit 270, the contacts 101 fit exactly into the electrically insulated contacts 380 of the base unit 270. Also, these contacts 101 are of a length such that they pass through the separating wall 200 into the upper chamber 70 by means of the electrical connecting leads 110 of the electric appliance 120 are connected with the contacts 130. The metal plate 40 is secured to the lower side of the separating wall 200 of the adapter 100 by means of a screw 60, and is so positioned that when the adapter 100 is received by the base unit the metal plate 40 electrically bridges the insulated contacts 390 of the base unit 270. The metal plate 40 is provided with a rivet 50 of such a length as to project through the separating wall 200 and be electrically connected with the grounding contact 140 of the electric appliance 120 by means of the electrical connecting lead 110, to assure proper grounding of the electric appliance 120 when the latter is placed upon the base unit. After this connection is established, the adapter 100 is secured to the bottom side of the electrical appliance 120. 
     FIG. 4 depicts the position of the adapter 100 when properly seated on the base unit 270. The outer wall 80 of the adapter can be annular of another shape matching the shape of the bottom of the electrical appliance in question. In the exemplary embodiment depicted in FIGS. 5 and 6, the outer wall 80 is of circular annular shape. The diameter of this wall is so selected that it exactly rests upon the base unit 270 down to its upper side 160, thereby surrounding the upwardly projecting circular annular rim 270a of the base unit, and accordingly assuring a positive holding action and a single definite resting position. In the case of larger and heavier electrical appliances, the outer wall 80 of the adapter 100 is advantageously so dimensioned that the entire base unit 270 is enclosed, as indicated by numeral 90 in the drawing. 
     FIG. 5 depicts the adapter as seen from above with its annular wall 80 encircling its separating wall 200. In this perspective view, the upwardly projecting contacts 101 for the conduction of household current and the upwardly projecting pin 50 for the safety contact lead are clearly visible. 
     FIG. 6 depicts in perspective the bottom side of the adapter 100 with its annular outer wall 80 being shown in section. Clearly visible is the metal plate 40 which serves to electrically bridge the contacts 17, 18 of the auxiliary current path for the relay winding or windings. The metal plate 40 is mounted properly in place by means of a mounting screw 60 and additionally a rivet 50. 
     As will be clear from the foregoing, the basic concept of the invention is to so design an adapter attachable to an electrical appliance that a firm electrical connection between the appliance and a base unit can be established, not only with respect to the contacts of the main current path for the appliance, but also with repect to the grounding contact lead. The electrical connection is so designed that, when the appliance with the adapter attached thereto is lifted off the base unit, all of the electrical contacts of the latter cease to carry current and can, as a result, be physically contacted by the person using the appliance without danger. Furthermore, the electrical connections established with the circuitry described above are so designed that a current-carrying connection for the actual appliance current does not become established until after a current-carrying connection for the safety contact lead has been estahlished from the electrical appliance to the household wiring. Additionally, the inventive concepts include so designing the adapter and the base unit relative to each other as to make possible only a single well-defined positioning of the former upon the latter for establishing the various electrical connections discussed above, while simultaneously assuring a stable supporting of the electrical appliance itself. 
     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of circuits and constructions differing from the types described above. 
     While the invention has been illustrated and described as embodied in base units receiving adapters permanently or removably attached to particular household appliances, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.