Abstract:
A switch unit having a combined switch function and locking function for controlling industrial tools, both the locking function and the switch function being achieved magnetically.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a switch unit having a combined switching and locking function for controlling industrial tools, especially hand-held units, such as screwdrivers and drills. 
     BACKGROUND INFORMATION 
     Requirements on the performance of industrial tools are becoming ever greater, and the ratio of cost to benefit is especially being observed ever more critically. In all industries, the overall costs of production units are considered, and not only the acquisition price: the maintenance effort, replacement parts cost, failure rate, etc., in sum determine the service life costs of the unit. Naturally, productivity also plays a major role. Units that people like to use and that are easy to operate contribute to an increased productivity. For this reason, the user friendliness of a unit is an important differentiating feature for the suppliers of industrial tools. The actuating elements of a device are of greater meaning because they are often operated/used. An electrical or mechanical fault in such a small part can bring the unit to a standstill. The actuating elements (or switch units), among them switches, buttons and/or rotating or sliding elements have to be robust, easy to handle, able to be set in a clear manner and resistant to wear, to the greatest extent possible. 
     In units that are now on the market, actuating elements, such as switches and rotating knobs are furnished with a mechanical click point torque, in order to improve the operability and the unambiguity of the switching. The click point torque is generated by frictional elements or spring elements, as a rule, and the electrical switching function is implemented by an electromechanical switch. The service life of this type of actuating elements is limited by its mechanical properties, and its wear leads to a reduction in the MTBF (mean time between failures) of the unit. 
     SUMMARY OF THE INVENTION 
     Thus, the present invention is based on the object of making available an improved switch unit having combined switch function and locking function for controlling industrial tools, and at the same time, of avoiding the disadvantages of the usual design approaches. According to the present invention, these objects are attained by the switch unit. The switch unit having a combined switch function and locking function for controlling industrial tools has both a locking function and a switch function, both functions taking place on a magnetic basis. The switch unit is made up of two opposite rows of magnets, and each row is made up of at least two magnets. The distance between the enveloping magnet rows lying on opposite sides is essentially constant, the rows being relatively movable with respect to one another in the direction of the extension of the rows. Furthermore, the distance between the adjacent magnets of one row is essentially constant, and in one of the rows of magnets at least one magnetic field detector is provided. Consequently, the switch unit is almost free from wear, its properties are not time dependent, and the maintenance intervals provided for it are only dependent on the support of the rotary knob. Therefore, the switch unit is very robust. 
     In one row of magnets a magnetic field detector is provided, the detector replacing one magnet of a series and having two adjacent magnets. Moreover, the distance between the detector and each of the two magnets is approximately equivalent to the distance, or a multiple of the distance, between the magnets mounted in the opposite row. The magnets adjacent to the detector are mounted in such a way that the opposite sides have different magnetic poles. Conditional upon the simple geometry of the magnet rows, the advantages of this type of construction are that the magnets perform both locking functions and switch functions. This type of construction has the advantage that the magnet, whose magnetic field is detected by the detector, always lies directly opposite to the detector in the locked-in state. Thus the geometry ensures a consistent and reliable behavior of the switch unit. Advantageously, the magnets are also situated (magnetized) in such a way that a closed magnetic flux circuit is present independently of the setting of the switch unit, that is, the stray flux is minimized. 
     A Hall effect sensor is advantageously used as the detector, because it is not prone to wear, and may be constructed to be very small. For this reason, based on the type of construction, the detector is very flexible. It is also available as a standard product, and gives off a 1-bit output signal, which permits setting the rotary direction of a hand unit without adjustment or complicated signal processing. 
     In one additional advantageous specific embodiment, the switch unit is a rotary switch which has two switching states that correspond to two rotary directions of a hand unit. In order to keep the switch unit compact, and to increase the efficiency of the magnets, the magnets should be furnished with a ferromagnetic shield at their sides facing away from each other. This shield minimizes the stray flux losses, and thereby increases the effective magnetic flux of the circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic representation of the switching state “left” of a switch unit according to the present invention. 
         FIG. 2  shows a schematic representation of the switching state “right” of a switch unit according to the present invention. 
         FIG. 3  shows a cross section of a rotary switch according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Similar or similarly functioning components are characterized in the figures by the same reference numerals, to a great extent. 
       FIGS. 1 ,  2  and  3  show schematic representations of preferred forms of the present invention.  FIGS. 1 and 2  show a magnetic circuit including two rows of magnets  12 ,  13 , two ferromagnetic steel rings  2  assigned to the magnets, and a detector  4 ,  11 . According to the present invention, the row of magnets  13  is relatively movable with respect to row  12 , that is, row  12  is mounted in a fixed manner, whereas row  13  is able to be shifted in a left or right direction. The distance between the row  14  is also mechanically fixed, according to the present invention. However, the type and method of fixing is not shown in schematic  FIGS. 1 and 2 , and depends on the specific embodiment of the switch unit. 
     According to the present invention, detector  4 ,  11  always has to have a magnet  18  lying opposite to it, This results in the circuit only being able to assume two states, as shown. The two states are designated in the figures as “left”  16  and “right”  17 . If movable row  13  is designated as the active row, then two magnets  18 ,  19  are active and take a part in the circuit/locking. In  FIG. 1 , all magnets  5  taking part in the magnetic circuit are situated as follows. Magnetic flux  7  from magnet row  13  flows through detector  4 , through steel ring  2 , through magnet  20  and back again to opposite row  13 . The direction of the flux is detected by Hall sensor  4  and the output of the sensor is switched to the corresponding state. The very high permeability of ferromagnetic steel ring  2  takes care that almost the entire flux  7  flows through detector  4  and simultaneously screens the detector against external magnetic stray flux. 
     The two locked-in magnets  19 ,  20  take care that the position of magnet  18 , which switches the detector, of movable row of magnets  13 , remains constant under normal working conditions with reference to opposite row  12 , that is, that the vibrations and impacts to be expected during operation do not influence the state of the sensor output. If row of magnets  13  is shifted with respect to row  12 , for instance, from left  16  to right  17 , then the force has to be sufficient to overcome the click point torque of locked-in magnets  19 . As soon as the click point torque is overcome, row of magnets  13  may be moved to the right using minimum effort, until the two magnets  19  attract each other and lock in. If row of magnets  13  is shifted into switching state “right”  17 , the flux direction through the Hall sensor reverses direction, and because of that, the output of the sensor also switches over correspondingly. Ferrite magnets or occasionally geomagnets may be used, depending on the size of the switch, the click point torque required and the desired price/performance ratio. 
       FIG. 3  shows a cutout of the cross section of a rotary switch. The rotary switch has an axis of rotation  9 , a fixed row of magnets  12  and a rotatable row of magnets  13 . Switch rings  1  and base body  3  are made of a nonferromagnetic substance. Ferromagnetic steel rings  2  are incorporated into switch ring and base body  3 . The substance acts like air with regard to magnetic flux  7  and holds magnets  5  and detector  4  mechanically in a fixed position, without influencing the magnetic flux. 
     Row  13  can be turned left or right with respect to row  12 . The state shown in  FIG. 3  corresponds to switch state “left”  16  shown in  FIG. 2 . The detector of the rotary switch shown in  FIG. 3  has two output states which correspond to switch states left  16  and right  17 . If the rotary switch is used as a control element of a hand tool, for instance, of a screwdriver or a drill, then the two states could correspond to the two rotary directions of the hand too. 
     There is a possibility of operating the detector as an analog sensor, that is, to position the magnets in such a way that the rotary angle of the rotary switch is able to be recorded. The detector output is then evaluated as the analog signal. 
     LIST OF REFERENCE NUMERALS 
     
         
           1 . switch ring 
           2 . ferromagnetic steel rings 
           3 . base body 
           4 . magnetic field detector 
           5 . magnets 
           6 . rotary direction 
           7 . magnetic flux 
           8 . magnetic poling 
           9 . rotary axis 
           10 . locked-in state 
           11 . magnetic field sensor 
           12 . row of magnets (passive) 
           13 . row of magnets (active) 
           14 . opposite sides 
           15 . distance apart of the magnets 
           16 . switching state left 
           17 . switching state right 
           18 . switching magnets 
           19 . locked-in magnet 
           20 . locked-in magnet