Abstract:
A friction safety brake which is released by virtue of an electromagnet is disclosed. Extending from a machine wall is a shaft that is rotatable relative to the machine wall. The shaft is to be braked by the friction safety brake. The brake includes: a first assembly comprising a coil carrier, a coupling element, a flange plate, at least one first brake disk and an intermediate disk; and a second assembly comprising an armature disk, at least a second brake disk and the intermediate disk. The flange plate is coupled in an axial direction with the coil carrier by virtue of coupling elements and is independently movable relative to the armature disk in the axial direction such that two braking circuits are available. The first braking circuit includes the armature disk, the coil carrier and the flange plate ( 21 ) coupled to each other in the direction of rotation. And, the second braking circuit includes the intermediate disk being relatively axially displaceable with respect to the coil carrier and the machine wall.

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns a safety brake which is releasable via an electromagnet. 
     A safety requirement issued by regulatory bodies demands technical equipment to be provided with two separate braking circuits so that if one braking circuit should fail, a braking operation from the other braking circuit can be provided. This is the case for elevators constructed in accordance with elevator regulation TRA 200 DIN EN 81. 
     In accordance with the subject matter of German Gebrauchmuster 295 10 828 two brakes are spacially integrated. In this arrangement there are two armatures, two brake disks, two spring arrangements that press the armature disks against the brake disks, and a single electromagnet with a magnetic coil arranged between the armature disks and brake disks. This arrangement provides a functionally safe, inexpensive and compact system that provides two brakes that are independent of one another. 
     In order to save space and to simplify the brakes while maintaining the safety function of a braking operation, and thereby reduce the cost of brakes, these brakes were further developed as shown in German Gebrauchmuster 296 11 732.3. In this brake the electromagnet comprises a magnetic coil and coil carrier that surrounds a central shaft that is arranged to be axially displaceable, but not rotatable in the brake. In addition, a single armature disk  3  that is axially displaceable, but cannot be rotated in the brake, is arranged axially between one of two brake disks  2 ,  11  and the magnetic coil/coil carrier. Springs are tensioned axially between the magnetic coil/coil carrier and the single armature disk  3 . 
     A disadvantage of this twin circuit brake is that, on account of the placement of the magnetic coil in the region between the rotating brake disks, the heat that is generated on the brake disks during braking bears upon the coil from two sides. Thus, the coil is heated in accordance with the amount of frictional work done during braking. This heating can become significant, particularly in a high temperature environment, for example in warm countries. In order to prevent overheating of the coil it is necessary to limit the braking power correspondingly. 
     A further disadvantage of this twin circuit brake is that it is necessary to change the entire coil when the brake linings are changed. This means that an inconvenient amount of effort needs to be expended in order to change the parts subject to wear. 
     Obviously, this twin circuit brake also needs to comply with the aforementioned safety requirement. In particular, malfunction situations (jamming or seizure situations) that can affect the movable parts of the brake should be accounted for. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a two circuit brake that satisfies the aforementioned safety requirement. 
     Further, it is an object of the invention to provide a two circuit brake in which the heat generated by braking effect of the brake, in particular in the vicinity of electrical components, is as small as possible. 
     A further object of the invention is to reduce the amount of effort expended in servicing the brake, in particular in the changing of the wearable parts of the brake, such as the brake linings. 
     The brake should also be constructed in the simplest possible way, so that it is easy to manufacture. 
     These objects are achieved in accordance with the following description of the invention. 
     In the two circuit brake in accordance with the invention, the heat that is generated on the brake linings during braking is only conducted to one side of the coil carrier, and then only via the armature disk. The heat can thereafter be released to the environment via the exposed outer side of the coil carrier. In this way the temperatures that occur in the coil carrier are kept relatively low. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments for the invention will be described in the following, making reference to the figures, in which: 
     FIG. 1 is a longitudinal cross sectional view of the preferred exemplary embodiment shown in a non-energized condition, i.e. in the braked condition. 
     FIG. 2 is a longitudinal cross sectional view of an alternative exemplary embodiment of the invention, also in the braked condition. 
     FIG. 3 is a side view of a third embodiment of the invention. 
     FIG. 4 is a sectional view along the line A-B in FIG. 3 of the third embodiment of the invention. 
     FIG. 5 is a sectional view along the line C-D in FIG. 3 of the third embodiment of the invention. 
     FIG. 6 is a side view of a fourth embodiment of the invention. 
     FIG. 7 is a sectional view along the line A-B in FIG. 6 of the fourth embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a two circuit brake in accordance with the preferred embodiment of the invention, wherein the two circuit brake is in a the braked condition. The two circuit brake is attached to a machine wall or back-bearing plate  3  of a motor (not shown) in order to brake a rotatable shaft  7 . The shaft  7  has a collar  9  with longitudinal splines  11 . 
     A first friction lining rotor or brake disk  14  that is disposed closer to the machine wall  3  and is rotates with the shaft  7 , and a second friction lining rotor or brake disk  16  that is disposed further from the machine wall  3  and also rotates with the shaft  7 , are mounted on the collar  9  by virtue of longitudinally disposed splines  13 ,  15  that mesh with the longitudinal splines  11 . The mounting being such that the brake disks  14 ,  16  are displaceable longitudinally but are not rotatable with respect to the collar  9 . 
     Between the first brake disk  14  and the machine wall  3  there is provided an annular flange plate  21 . Between the first brake disk  14  and the second brake disk  16  there is provided an intermediate disk or plate  23 , and on the side of the second brake disk  16  that is facing away from the machine wall  3  there is provided an armature disk or plate  25 . The intermediate disk  23  serves as a friction surface for both the first brake disk  14  and the second brake disk  16 . The flange plate  21  serves as friction surface for the first brake disk  14 , and the armature disk  25  serves as friction surface for the second brake disk  16 . 
     On the side of the armature disk  25  that faces away from the machine wall  3  there is provided an annular coil carrier  30 , through a central opening  31  of which the shaft  7  projects coaxially. 
     The flange plate  21 , the intermediate disk  23 , the armature disk  25  and the coil carrier  30  are arranged coaxially with respect to one another and have essentially the same diameter. The shaft  7  passes through all of these components. 
     The coil carrier  30  is mounted a fixed distance from the flange plate  21  by an arrangement consisting of several connection screws  35  and associated spacing bushes  36 . For this purpose the coil carrier  30  has several, preferably three, bores  32  around its circumference that extend in an axial direction therethrough. At the end of each bore  32  of the coil carrier  30 , that is furthest from the machine wall  3 , there is a countersink  34  provided for the head of the corresponding connecting screw  35 . In addition, in the flange plate  21  coaxial with these bores there are provided corresponding threaded bores  33 . A spacing bush  36  is provided between each threaded bore  33  of the flange plate  21  and each bore  32  of the coil carrier  30 , respectively. The spacing bushes  36 , with their connecting screws  35 , pass through respective bores  23   b in the intermediate disk  23  and concentrically placed notches  38  in the armature disk  25 . Furthermore, an O-ring  39  is provided around each spacing bush  36  where it passes through the bore  23   b . The O-ring  39  serves to guide the spacing bush  36  in the bore  23   b of intermediate disk  23 , and thereby provides radial location for the flange plate  21  and the coil carrier  30 . 
     The coil carrier  30  is spaced a predetermined distance from the flange plate  21  by virtue of the spacing bushes  36 , and is held by virtue of the connecting screws  35  which extend between the threaded bores  33  in the flange plate  21  and the countersinks  34  in the coil carrier  30 . 
     The intermediate disk  23  disposed between the first brake disk  14  and the second brake disk  16  is fixed to and spaced from the machine wall  3  a predetermined distance by virtue of a plurality of fixing screws  37  equally distributed in a circular arrangement in the machine wall  3  and coaxial with the shaft  7 . For this spacing, bushes  37   a  are disposed between the intermediate disk  23  and the machine wall  3 . The fixing screws  37  are screwed into corresponding threaded bores  41  provided in a circular arrangement, and pass through the spacing bushes  37   a.  Furthermore, bores  42  are provided in the intermediate disk  23  also in a circular arrangement, with the bores  42  being coaxial with the threaded bores  41  when the intermediate disk  23  is mounted to the machine wall  3 . The fixing screws  37  pass through these bores  42 . 
     Each fixing screw  37 , as seen from the side of the machine wall  3 , further passes through a respective bore  44  in the armature disk  25 , and the head or the end of each fixing screw  37  projects away from the machine wall  3  and penetrates respectively to a small extent into a bore  45  provided in the coil carrier  30 . At the head or end of each fixing screw  37 , or more exactly, between the head or end of each fixing screw  37  and a respective circular depression  46  provided on the intermediate disk  23 , an intermediate sleeve  47  is disposed that penetrates at least to a substantial extent into a respective associated bore  44  in the armature disk  25 . 
     Preferably, the connecting screws  35  and the fixing screws  37  are provided in the same circular arrangement, and alternate with each other with equal spacing. 
     The coil carrier  30  is partially open on the side facing the armature disk  25 , and is provided with an end wall  51  on the side that is furthest from the machine wall  3 . A magnetic coil  55  is immovably embedded, by virtue of a molding resin or a substance having similar properties, in an appropriately formed cut-out  53  in the coil carrier  30 . The magnetic coil  55  together with the coil carrier  30  form the electromagnet of the brake. 
     The armature disk  25  serves as the reaction surface for the second brake disk  16  in the braking condition. In the braking condition, shown in FIG. 1, a plurality of springs  57  that are insert in the coil carrier  30 , press the armature disk  25  away from the coil carrier  30  and against the second brake disc  16  in order to apply the desired braking effect. The springs  57  are disposed at equal spacing with respect to one another, and are located radially inside of the magnetic coil  55 . 
     In the following, the function of the embodiment of the two circuit brake described with respect to FIG. 1 will be described. 
     FIG. 1 shows the brake in the braked condition. This occurs when electrical energy is not applied to the magnetic coil  55  in the coil carrier  30  such that the springs  57  press the armature disk  25  against the second brake disk  16 . Because the connecting screws  35  maintain the coil carrier  30  at a predetermined distance from the flange plate  21 , which lies between the machine wall  3  and the first brake disk  14 , the pressing of the armature disk  25  against the brake disk  16  causes the latter to press on the intermediate disk  23 . The distance of the intermediate disk  23  to the machine wall  3  is fixed by the spacing bushes  37   a  so that the intermediate disk  23  cannot move towards and be forced against the first brake disk  14 . 
     The distance between the coil carrier  30  and the flange plate  21  is fixed by the spacing bushes  36 . Thus, in operation of the brake the springs  57  urge the armature disk  25  and the coil carrier  30  apart, and in particular press the coil carrier  30  away from the armature disk  25 , such that the flange plate  21  is urged against the first brake disk  14 , which in turn is urged against the intermediate disk  23 . 
     In this way during operation of the brake, both the first brake disk  14  and the second brake disk  16  are braked from both sides. 
     In the released condition of the two circuit brake in accordance with the invention, the magnetic coil is energized so that the armature disk  25  is pulled towards the coil carrier  30  against the force of the springs  57 . Because the distance between the coil carrier  30  and the flange plate  21  is fixed by the fixing screws  35  and the spacing bushes  36 , the distance between the flange plate  21  and the armature disk  25  increases. The relative position of the intermediate disk  23  to the machine wall  3  is fixed by the spacing bushes  37   a  and the fixing screws  37 . Both brake disks  14  and  16  are axially displaceable on the shaft  7  by virtue of their longitudinal splines  13  and  15  and the longitudinal splines  11  of the shaft collar  9 . In the released condition of the brake, the first brake disk  14  and the flange plate  21  on one side, and the second bake disk  16  and the armature disk  25  on the other side, are therefore, moveable to a small extent relative to the intermediate disk  23 . 
     In the transition from the braked condition to the released condition, the assembly consisting of the flange plate  21  and the coil carrier  30 , held apart by the connecting screws  35  and the spacing bushes  36 , moves slightly towards the machine wall  3 . At the same time the spacing bushes  36  with their O-rings slide and are guided within the bores  23   b  of the intermediate disk  23 . 
     The two circuit brake in accordance with the invention as shown in FIG. 1 compensates for both malfunction conditions (jamming conditions) set out below, that can occur in the transition from the released to the braked condition. In both malfunction conditions braking is achieved. 
     Firstly, a jamming of the armature disk  25  with respect to the guide sleeve  47  is overcome. In this case the armature disk  25  does not move further towards the second brake disk  16 , however, the springs  57  effect a pressing apart of the armature disk  25  and the coil carrier  30  to the same extent as in the normal condition. Because the connecting screws  35  and the spacing bushes  36  hold the coil carrier  30  and the flange plate  21  at a predetermined distance from one another, the flange plate  21 , on account of the urging away of the coil carrier  30  from the armature disk  25 , moves in a direction away from the machine wall  3  towards the first brake disk  14 . In this way the flange plate  21  presses against the first brake disk  14 , which thereby presses against the intermediate disk  23  on account of the slideability of the first brake disk  14  on the collar  9 . In this way a braking by at least one of the braking circuits is achieved during this jamming condition. 
     Secondly, during transition from the released to the braked condition, a jamming of at least one of the spacing bushes  36  in the corresponding bore  23   b  in the intermediate disk  23  is overcome by the arrangement in accordance with the invention. If a seizure jam) occurs at this location at least the armature disk  25  is pressed against the second brake disk  16  by virtue of the springs  57 , so that one of the braking circuits of the two circuit brake functions. 
     In the two circuit brake in accordance with the invention and shown in FIG. 1 there are the following force flux lines. 
     In the normal situation, a force flux line extends from the spring  57  through the armature disk  25  and the second brake lining  16  to the intermediate disk  23 . This force flux line is closed by a force flux line that begins at the end of the spring  57  remote from the armature disk  25  and proceeds through the coil carrier  30  to the connecting screws  35  and the spacing bushes  36 . From there it reaches the intermediate disk  23  via the first brake disk  14  to close the force flux path. 
     In the first jammed condition, that is upon seizure of the armature disk  25  with the guide sleeve  47 , a force flux line that begins at the end of the spring  57  remote from the armature disk  25  runs through the coil carrier  30  to the connecting screws  35  and the spacing bushes  36  to the flange plate  21 . From there it reaches the intermediate disk  23  via the first brake disk  14 . This force flux line is closed by a force flux line that reaches the intermediate disk  23  from the springs  57  through the armature disk  25 , and from there, on account of the seizure, through the guide sleeves  47  to the intermediate disk  23 . 
     In the second jammed condition, that is upon seizure of at least one of the spacing bushes  36  in its corresponding bore  23   b  of the intermediate disk  23 , the closed force flux line runs from one of the springs  57 , to the armature disk  25 , and from there through the second brake disk  16  to the intermediate disk  23  to the other end of the spring  57 , i.e. the end facing away from the armature disk  25  through the coil carrier  30  to the connecting screws  35 , and from there, on account of the seizure of the spacing bushes  36  likewise to the intermediate disk  23 . 
     The following modifications of the two circuit brake embodying the invention and described with respect to FIG. 1 are envisaged. 
     An adjustment of device, for example a set screw  71  could be used for adjustment of the springs  57 . 
     The number of springs  57 , connecting screws  35  and bushes  36 , as well as the number of fixing screws  37  with bushes  37   a,  and guide bushes  47  can be different from that described above. 
     Now follows a description of a two circuit brake embodying the present invention and shown in FIG.  2 . In this embodiment, components which have the same function are identified by the same reference numerals as in the above described embodiment. 
     In this embodiment, in the released state of the brake an outer ring or a drum  3  rotates about a shaft  7 . The shaft has a collar  9  on which there is mounted a bearing  4  to support the drum  3 . In the braked condition, shown in FIG. 2, the drum  3  is stationary with respect to the shaft  7 . 
     The intermediate disk  23  is secured onto the collar  9  by virtue of several collar screws or fixing screws  37  that are screwed into the radial side of the collar  9  that faces away from the drum  3 , and are distributed evenly around the circumference of the intermediate disk  23 . Thereby, the intermediate disk  23  is axially located not only relative to the drum  3 , but also relative to the shaft  7 . The intermediate disk  23  has evenly distributed in a circular arrangement several bores  23   b  through which the connecting screws  35  with spacing bushes  36  penetrate. On the outer surface of the spacing bushes  36  in the vicinity of the bore  23   b  there is an O-ring  39  for the purpose of guiding the spacing bush  36  within the bore  23   b.    
     The connecting screws  35  connect a cylindrically shaped flange plate  21 , that is disposed between the drum  3  and the intermediate disk  23 , to the coil carrier  30 . The flange plate  21  has for this purpose several threaded bores  33  to receive the connecting screws  35 . In the direction facing away from the drum  3  are, in addition to the intermediate disk  23 , an armature disk  25  and the coil carrier  30 . The coil carrier  30  has bores  32  with countersinks  34  disposed at their ends away from the drum  3  for receiving corresponding heads of the connecting screws  35 . The armature disk  25  has recesses  38 . Bores  32 ,  33 ,  23   b  and recess  38  correspond with each other in their number and also their radial and circumferential position, so that the connecting screws  35  and their spacing bushes  36  penetrate through the intermediate disk  23  and the armature disk  25 , and at the same time hold the flange plate  21  a predetermined distance from the armature disk  30 . Thus, the arrangement consisting of the flange plate  21 , the coil carrier  30 , the connecting screws  35  and the spacing bushes  36  is slidably disposed relative to the shaft  7  and to the intermediate disk  23 . 
     The intermediate disk  23  further has bores  44  that are also evenly distributed in a circular arrangement having a radius larger than that of the circular arrangement of the bores  23   b  for the spacing bushes  36 . Guide pins or bolts  47 , at least partly, pass through these bores  44  and are pressed into corresponding bores in the armature disk  25 . The guide pins  47  serve as guides for the armature disk  25  with respect to the intermediate disk  23 . 
     The flange plate  21 , the intermediate disk  23 , the armature disk  25  and the coil carrier  30  are coaxially disposed with respect to one another and have essentially the same outer diameter. The shaft  7  passes through the flange plate  21 , the intermediate disk  23 , the armature disk  25  and the coil carrier  30 . 
     Along the outer circumference of the drum  3  are several fastening screws  10  that are evenly distributed about the circumference of the drum  3  and penetrate through a respective bush  11  disposed between the head of the fixing screw  10  and the drum  3 . The bushes  11  hold a first friction lining carrier  14   a  and a second friction lining carrier  16   a  in a slidable manner. The friction lining carriers  14   a,    16   a  are ring shaped and have corresponding bores along their circumferences, so that they fit on the bushes  11 . A respective brake lining  14   b,    14   c;    16   b,    16   c  is glued on both sides of each friction lining carrier  14   a,    16   a  at respective inner peripheries thereof. The intermediate disk  23  has an outer edge portion or a tongue  23   c  that has a smaller thickness than the rest of the intermediate disk  23 . The tongue is, however, of constant thickness over its radius. The respective brake lining  14   b,    14   c;    16   b,    16   c  of the friction lining carrier  14   a,    16   a  is, when viewed radially disposed in the region of the tongue  23   c,  and extends not quite as far as the inner radius of the tongue  23   c.  In addition the first friction lining carrier  14   a  is disposed on the side of the tongue  23   c  nearest the drum  3  between the flange plate  21  and the tongue  23   c,  while the second friction lining carrier  16   a  is disposed on the side of the tongue  23   c  that is furthest from the drum  3  between the armature disk  25  and the tongue  23   c.  With this arrangement a braking effect can be achieved when the brake lining  14   b  facing the flange plate  21  is pressed against the flange plate  21 , the brake linings  14   c  and  16   b  facing the tongue  23   c  is pressed against the tongue  23   c,  and the brake lining  16   c  facing the armature disk  25  is pressed against the armature disk  25 . 
     The coil carrier  30  is, as in the exemplary embodiment described with respect to FIG. 1, on the side facing the armature disk  25  partially open and is provided with an end wall on the side facing away from the drum  3 . In the coil carrier  30  is a correspondingly shaped cut-out  53  in which a magnetic coil  55  is embedded by virtue of a casting resin or equally effective material. The magnetic coil  55  together with the coil carrier  30  forms the electromagnet of the brake. 
     Furthermore, a plurality of springs  57  are provided in corresponding bores in the coil carrier  30 , with the bores being evenly spaced around the circumference of the coil carrier  30  and open on the side facing the armature disk  25 . If the magnetic coil  55  is not energized the springs  57  press the armature disk  25  away from the coil carrier  30 . 
     The axial position of the intermediate disk  23  is fixed in the embodiment shown in FIG. 2, as it is in the embodiment described with respect to FIG.  1 . The assembly consisting of the flange plate  21 , the coil carrier  30 , the spacing bush  36  and the connecting screws  35  are displaceably disposed with respect to the intermediate disk  23 . Also, the armature disk  25  is moveable with respect to the coil carrier  30  in response to the force exerted by the springs  57  and the magnetic coil  55 . The brake linings  14   b,    14   c  and  16   b,    16   c  are positioned axially to abut the flange plate  21  and the armature disk  25 . 
     Now follows a description of the two circuit brake embodying the present invention and described with respect to FIG.  2 . 
     The non-energized or braked condition of this embodiment is shown in FIG.  2 . With a non-energized magnetic coil  55  the springs  57  press the armature disk  25  against the second friction lining carrier  16   a  that, on account of its displaceability on the bush  11 , presses against the intermediate disk  23 . The springs  57  exert a force on the coil carrier  30  in a direction away from the intermediate disk  23 . This force is conducted via the connecting screws  35  and the spacing bushes  36  to the flange plate  21 , and thereby via the first friction lining carrier  14   a  to the intermediate disk  23 . In this condition all of the brake linings  14   b,    14   c  and  16   b,    16   c  exert a braking effect. 
     In the released condition of the brake current flows into the magnetic coil  55  and the armature disk  25  is pulled against the spring  57  and then against carrier  30 . Thus, the distance between the flange  21  and the armature disk  25  increases while, on account of the slideability of the spacing bushes  36  in the intermediate disk  23 , the friction lining carriers  14   a  and  16   a  with their associated brake linings  14   b,    14   c ,  16   b,    16   c  release from their braking engagement with the intermediate disk  23 . 
     The two circuit brake in accordance with the invention and described with respect to FIG. 2 covers the following two malfunction (jamming) conditions. 
     First, if the spacing bushes  36  seizes in the bore  23   b  there is at least a braking effect caused by the armature disk  25 , the second friction lining carrier  16   a  and the intermediate disk  23 . 
     Second, in the event of the seizure of the guide pin  47  in the intermediate disk  23  a braking effect is provided by virtue of the flange plate  21 , the first friction lining carrier  14   a  and the intermediate disk  23  as the spring  57 , in reaction to this seizing condition exerts a pressure on the coil carrier  30  in a direction away from the drum  3 , whereby a force is conducted via the spacing bushes  36  onto the flange plate  21 . In the embodiment of FIG. 2 there are the following closed force flux lines. 
     In the normal situation there is a force flux line emanating from the spring  57  that transfer its force via the second friction lining carrier  16   a  to the intermediate disk  23 . Also emanating from the spring  57  there is a flux line via the coil carrier  30 , to the spacing bushes  36  and to the flange plate  21 , and from there via the first friction lining carrier  14   a,  onto the opposite side of the intermediate disk  23 . 
     Further in the first mentioned jammed condition, a force flux line from the spring  57  passes onto the armature disk  25 , and from there to the second friction lining carrier  16   a  and then onto the intermediate disk  23 . At the same time a force flux passes from the spring  57  onto the coil carrier  30 , and via the spacing bushes, on account of the seizure, onto the intermediate disk  23 . 
     In the second mentioned jammed condition, (seizure of the guide pins  47 ) a force flux line runs from the spring  57  onto the armature disk  25  and the guide pin  47 , and from there, on account of the seizure, onto the intermediate disk  23 . At the same time a force flux line runs from the spring  57  onto the coil carrier  30  and from there, via the spacing bushes  36  and the first friction lining carrier  14   a,  onto the intermediate disk  23 . 
     The following alternative arrangements of the two circuit brake of the embodiment of the invention described in respect to FIG. 2 are envisaged. 
     For the adjustment of the springs  57  there can be provided an adjustment device, for example an adjustment screw  71 . 
     The number of fixing screws  37 , of springs  57 , of connecting screws  35  with spacing bushes  36 , and the number of fixing screws  10  with bushes  11  can also differ from that described above. 
     Instead of fixing screws  37  there can be provided other connections between the shaft  7  and the intermediate disk  23 . 
     The embodiment described with respect to FIG. 2 can also be constructed with a fixed drum  3  and a rotating shaft  7 . 
     In the following, the third embodiment of the invention will be described with reference to FIGS. 3,  4  and  5 . Components that have the same function as corresponding components in the first or second embodiments will be given the same reference numbers. 
     The third embodiment shown in FIGS. 3,  4 ,  5  has, in common with the embodiment of FIG. 1, a rotating shaft  7  of a motor (not shown) with a collar  9 , on which an intermediate disk  23  is fixed by virtue of several fixing screws  37  uniformly positioned around the circumference of the intermediate disk  23 . Between the machine wall or an end bearing  3  of the motor and the intermediate disk  23  is a flange plate  21 . On the side of the intermediate disk  23  that is furthest from the machine wall  3  there is provided an armature disk  25  and a coil carrier  30  with a magnetic coil  55  and several springs  57  distributed uniformly around the circumference of the coil carrier  30 . 
     In a manner analogous to the arrangement shown in FIG. 2, the axial spacing between the flange plate  21  and the armature disk  25  adjusts itself on several spacing bushes  36   a  which extend in the axial direction and are distributed around the circumference of the brake. On the end of each spacing bush  36   a  that is furthest from the machine wall  3  there is provided a bush  36   b.  The end of each bush  36   b  that is furthest from the machine wall  3  projects into a respective bore of the coil carrier  30 . To provide further guiding of the bush  36   b  an O-ring  39  is fixed to the outer surface of the bush  36   b.  This O-ring  39  fills the space between the bush  36   b  and the corresponding bore of the coil carrier  30  at an appropriate place. 
     Each spacing bush  36   a  together with the bush  36   b  is fixed by virtue of a fixing screw  37  to the machine wall  3 . It is also envisaged that there is provided a spacing sleeve  61  between the spacing  36   a  and the machine wall  3 . Between the spacing sleeve  61  and the spacing bush  36   a  is an arc shaped first spring lamella or leaf spring  63  that is centrally secured therebetween. Around the entire circumference of the brake there are preferably provided three uniformly distributed first spring lamella or leaf springs  63 , each extending the same arc. On a free end of each first spring lamella or leaf spring  63  the flange plate  21  is fixed by virtue of rivets  65 . The flange plate  21  is thereby suspended on the first spring lamella or leaf spring  63  in a resilient manner and is axially displaceable with respect to the machine wall  3  and the intermediate disk  23 . Along a circumferential edge portion of the flange plate  21 , a first brake lining  14  is glued on the side of the flange plate  21  facing the intermediate disk  23 . 
     Between each spacing bush  36   a  and each bush  36   b  a second spring lamella or leaf spring  67  is fixed at its middle. On free ends of each second spring lamella or leaf spring  67  there is suspended the armature disk  25  by virtue of rivets  69  in a manner such that the armature disk  25  is resiliently and axially moveable with respect to the intermediate disk  23 . Along a circumferential edge of the armature disk  25  on the side facing the intermediate disk  23  there is glued a second brake lining  16 . 
     Between each two rivets  65  (or  69 ) are disposed the spacing bushes  36   a  which extend between the flange plate  21  and the coil carrier  30 . Provided for each spacing bush  36   a  is a corresponding bore in the flange plate  21 , a respective bore in the coil carrier  30  and a corresponding screw. 
     The assembly consisting of the flange plate  21 , the spacing  36   a  and the coil carrier  30 , and in the same manner the armature disk  25 , are independently axially displaceable with respect to the intermediate disk  23 . 
     An adjustment screw  71  is screwed in the rear side of the coil carrier  30 , which adjustment screw  71  positions the end of each spring  57  that is remote from the armature disk  25 , so as to adjust the spring force acting on the armature disk  25 . As shown in FIG. 5, in addition to the springs  57 , that are radially inward of the magnetic coil  55  and extend in an axial direction, there are also springs  57   a  that also extend in an axial direction in the coil carrier  30 . 
     In the following there will be described the function of the third embodiment according to FIGS. 3,  4  and  5 . 
     In the braked condition shown in FIGS. 3,  4  and  5 , the magnetic coil  55  is not energized and therefore the springs  57 ,  57   a  press the armature disk against the intermediate disk  23 . As soon as this happens the coil carrier is moved by the springs  57 ,  57   a  in a direction away from the intermediate disk  23 . This causes the flange plate  21 , on account of the spacing bushes  36   a,  to move into braking engagement with the intermediate disk  23 . In the normal situation both the armature disk  25  and the flange plate  21  are in braking contact with the intermediate disk  23  by virtue of their associated brake linings  14 ,  16 . 
     In the released state of the brake, the magnetic coil  55  is energized and attracts the armature disk  25 . The space between the armature disk  25  and the flange plate  21  thereby increases. In this situation neither the flange plate  21  nor the armature disk with its brake lining  14 ,  16  are in braking engagements with the intermediate disk  23 . 
     The embodiment according to FIGS. 3,  4  and  5  overcomes all of the jammed conditions that can be imagined affecting the moveable parts, and that correspond to the jammed situations described with respect to the earlier described embodiments. 
     In this third embodiment, in a place of the leaf springs or spring lamella  63 ,  67  other spring elements can be used. 
     Also the number of springs  57 , the number of rivets  65 ,  69  the number of fixing screws  37  with their spacing sleeves  61 , and the number of bushes  36   b,    36   a  can also differ from that described. 
     In the following, a fourth embodiment will be described with reference to FIGS. 6 and 7. Components that have the same function as corresponding components in the first, second or third embodiments bear the same reference numerals. 
     In a manner analogous to the embodiment described with respect to FIGS. 3 to  5 , the fourth embodiment has a machine wall  3 , a shaft  7  with a splined collar  9  that rotates but is fixed in an axial direction, a coil carrier  30  with armature disk halves  25   a,    25   b,  and a rotatable intermediate disk  23  between the machine wall  3  and the armature disk halves  25   a,    25   b.  A first brake lining  14  is glued at a circumferential edge portion of the intermediate disk  23  on the surface of the intermediate disk  23  facing the machine wall  3 . In addition, on the side of the intermediate disk  23  facing away from the machine wall  3  there is a coil carrier  30 , and between this coil carrier  30  and the intermediate disk  23  there are the first armature disk half  25   a  and the second armature disk half  25   b.  The armature disk halves  25   a,    25   b  form essentially two separate semi-circular or arcuate segments extending for about 180°. On the circumferential edge portion of each armature disk half  25   a,    25   b  on the surface facing the intermediate disk  23  there is glued a second brake lining  16 . The coil carrier  30  houses a magnetic coil  55  and several springs  57  extending in an axial direction and located radially inside of the magnetic coil  55 , and several springs  57   a  extending in an axial direction and located radially outside of the magnetic coil  55 . For each spring a respective axially extending bore is in the coil carrier  30 . The springs  57  that are radially inward with respect to the magnetic coil  55  are adjusted by virtue of an adjustment screw  71  that is screwed into the side of the coil carrier  30  that faces away from the machine wall  3 . 
     The intermediate disk  23  has on its radially inward side longitudinal splines  13  that mesh with longitudinal splines  11  on the radially outer surface of the splined collar  9 . 
     The coil carrier  30  is fixed in the axial direction to the machine wall  3  by virtue of several fixing screws  35  each having a corresponding spacing sleeve  61  and a spacing bush  36 . The spacing sleeve  61  is disposed between the machine wall  3  and the coil carrier  30 . Between the spacing sleeve  61  and the spacing bush  36  are a total of two arc shaped spring lamella or leaf springs  67   a,    67   b  that each extend half of the circumference of the brake. Each spring lamella or leaf spring  67   a,    67   b  has the same length. The design of each spring lamella or leaf spring  67   a  and  67   b  is such that its outer radius is equal to the outer radius of the coil carrier  30 . In its relaxed condition, the longitudinal disposition of the spring lamella or leaf springs  67   a  and  67   b  is in the circumferential direction of the coil carrier  30 . At two spaced apart locations on the longitudinal extent of each spring lamella or leaf spring  67   a,    67   b  there is fixed by virtue of two rivets  69   a  the half of the armature disk half  25   a,  and by virtue of two rivets  69   b  the armature disk half  25   b,  so that these armature disk halves  25   a,    25   b  are suspended so as to be axially displaceable and resiliently mounted with respect to the coil carrier  30 . In the preferred embodiment the rivets  69   a  and  69   b  are arranged, when viewed in the circumferential direction, alternating and with the same spacing as the fixing screws  37 . 
     In the braked condition, as shown in FIGS. 6 and 7 the magnetic coil  55  is not energized, the springs  57   a,    57   b,  press both armature disk halves  25   a  and  25   b  and the second brake linings  16  against the intermediate disk  23 . The brake lining attached to the intermediate disk  23  is pressed against the machine wall  3 , which performs the function of the flange plate of the other embodiments. 
     In the released condition, the magnetic coil  55  is energized and both armature disk halves  25   a  and  25   b  attracted to the inner side of the coil carrier  30 . In this way the armature disk halves  25   a  and  25   b  no longer press against the intermediate disk  23 , and thus the intermediate disk no longer presses against the machine wall  3  so that the brake is released. 
     Also, in this embodiment all simple jammed conditions that can affect the moving parts and that can occur in the transition to the braked condition are accounted for. 
     Upon seizure of one armature disk half, for example the armature disk half  25   a,  the other armature disk half  25   b  is moveable. 
     In accordance with the embodiment of FIGS. 6 and 7 there are in particular the following alternatives that are possible. 
     In place of the splines between the collar  9  and the intermediate disk  23 , there could be a lamella or plate which is able to transmit torque and yet remain axially moveable. 
     In place of the lamella springs or leaf springs  67   a,    67   b  other spring elements can be used. 
     The number of springs  57   a,    57   b,  the number of rivets  69   a,    69   b  and the number of fixing screws  35  with spacing bushes  36  can be different from that described. 
     The features of each component of one described embodiment can alternatively be replaced by the features of this component from another embodiment, as long as the corresponding described braking function is not changed.