FIELD 
     The invention relates to an actuator for actuating an elevator brake. 
     BACKGROUND 
     The elevator installation is installed in a building. It essentially consists of a car which is connected by way of support means with a counterweight or with a second car. The car is moved along substantially vertical guide rails by means of a drive which selectably acts on the support means or directly on the car or the counterweight. The elevator installation is used to convey persons and goods within the building over individual or several floors. 
     The elevator installation includes devices in order to safeguard the elevator car or also a counterweight in the case of failure of the drive or support means or in the case of other faulty behavior. For that purpose, use is usually made of elevator brakes which when required can brake the elevator car or the counterweight on the guide rails. These elevator brakes are increasingly actuated by electromechanical actuators. 
     An actuator of that kind is known from International Application WO2011/113754, which can actuate a pair of elevator brakes synchronously. This actuator counteracts possibly arising impact and shock loads by use of damping devices such as hydraulic, pneumatic or magnetic damping devices. Impact noise and material loads are thus reduced. It is unsatisfactory in that regard that actuation speed is slowed down by the use of damping devices of that kind. 
     SUMMARY 
     The invention has the object of providing an actuator which can accept impact and shock loads without negative influence on actuation speed. 
     In one embodiment an electromagnetic actuator for attachment to an elevator car of an elevator installation is provided. The electromechanical actuator is provided for actuation of a brake. For that purpose it includes an energy store, a retaining device, a resetting device and at least one connecting device for connecting the actuator with the brake or the brake equipment. The resetting device serves for resetting the electromechanical actuator into a first operating position corresponding with a readiness setting of the brake. It is also intended to transmit a retaining force for retaining the brake in the first operating position corresponding with the readiness setting. The resetting device in that case preferably acts, for retaining as well as resetting, on the energy store and the connecting element by way of the retaining device. The energy store for its part is so arranged that when required and when the retaining device is released it can act on the connecting element in order to actuate the brake and bring it into a corresponding applied setting. 
     Advantageously, the energy store acts on the connecting element by way of a trigger lever. This trigger lever is held in the readiness setting at a connecting point of a retaining electromagnet arranged at the retaining device. The retaining device is preferably arranged on a return lever, and a fulcrum of the return lever and a fulcrum of the trigger lever are arranged on a common axis. It is thus ensured that a pivot radius of the connecting point of the retaining device and of the trigger lever are the same. The connecting points can thus be moved synchronously with respect to one another in simple manner. 
     Advantageously, the connecting element for connecting the actuator with the brake is guided by way of the fulcrum of the trigger lever. The connecting element for that purpose includes a connecting strap which is connected on the one hand with the fulcrum of the trigger lever and on the other hand with the brake or brakes. 
     The resetting device of the electromechanical actuator advantageously includes recoil prevention means, preferably spring-loaded recoil prevention means, which relieves the resetting device of recoil forces. This is advantageous and useful, since the brakes can on occasion press back the connecting element of the electromechanical actuator. This can happen during a resetting process or it can also be the case that the connecting element is positioned in an intermediate position if, for example, a brake is not completely applied, since the elevator car has already come to a stop beforehand. In such cases the recoil prevention means prevents overloading or even damage of the resetting device and the entire actuator. 
     Advantageously, the energy store includes an impact buffer which reduces force shock when the energy store impinges in an end position. This is advantageous, since the energy store has stored a large amount of energy. In the usual case this energy is transmitted to the brake by way of appropriate connecting rods for actuation of the brake. In special cases, if, for example, a brake is not yet installed or when operations are carried out at the time of placing into service, this energy cannot be transmitted. The impact buffer in cases of that kind prevents overloading of material. 
     Advantageously, the resetting device, for the purpose of resetting the actuator into and retaining it in the first operating position corresponding with the readiness setting of the brake, acts on the retaining device by way of the recoil prevention means. The recoil prevention means is constructed for transmitting force in merely one direction. The recoil prevention means of the resetting device thus ensures that the resetting device is not subjected to uncontrolled loading. Insofar as, as previously stated, the connecting element is in an intermediate position it is thus ensured that the resetting device can operate and transmit force only in one line of action of force. Depending on the form of construction of the actuator and the resetting device this direction can be pulling or pushing. The resetting device is preferably designed for transmitting a tension force. 
     Advantageously, the resetting device is connected with the retaining device by way of a return carriage and this return carriage includes the recoil prevention means. For that purpose, the recoil prevention means includes, for example, a slot which co-operates with a guide pin integrated in the retaining device. An embodiment of that kind is advantageous with respect to production. In addition, the resetting device advantageously includes a spindle drive with a spindle nut. The spindle nut is arranged in the return carriage. A geared motor drives a return spindle co-operating with the spindle nut. The return carriage can thus be moved back and forth. 
     Advantageously, the retaining device is connected with a counterspring, which urges the retaining device together with the guide pin into the position corresponding with the first direction of the recoil prevention means. The recoil prevention means is thus a spring-loaded recoil prevention means. The force effect of the counterspring is in that case small by comparison with the force effect of the energy store. 
     The energy store of the electromechanical actuator is advantageously connected with the connecting element by way of a trigger lever. The energy store accordingly acts on this connecting element by way of the trigger lever. This trigger lever includes a connecting point. The trigger lever is held in the readiness setting at this connecting point by a retaining electromagnet arranged at the retaining device. The retaining device is in turn arranged on a return lever. A fulcrum of the return lever and a fulcrum of the trigger lever are arranged on a common axis or shaft so that a pivot radius of the connecting point of the retaining device and that of the trigger lever are the same. This is advantageous, since it is ensured by this arrangement that in the case of return or resetting of the trigger lever into the readiness setting the retaining device transits a path identical to the connecting point of the trigger lever. 
     The connecting element is advantageously guided by way of the fulcrum of the trigger lever and the connecting element further includes a connecting strap which is connected with the fulcrum of the trigger lever. The connecting element is preferably a shaft, which, for example, is rotatably or pivotably mounted in a housing of the actuator and to which the trigger lever and the connecting strap are secured. This shaft forms the fulcrum of the trigger lever. Use of a connecting strap of that kind is advantageous, since adaptation to required actuation paths can be carried out by the geometric form of this strap. The actuator itself can thus be left at that; it only has to be adapted to the connecting lever. 
     Advantageously, the energy store of the electromechanical actuator, in addition to the previous solutions or also as an alternative design, includes the impact buffer. For that purpose the energy store includes, for example, a first part, a second part and a first spring with a first spring stressing force. In that case, this first spring is stressed between the first part and the second part. The first part and the second part are assembled together to be displaceable over a displacement range. The displacement range is bounded by at least one first, i.e. front, abutment or second, i.e. rear, abutment. This at least one abutment is used for ensuring a minimum first spring stressing force. The energy store is correspondingly so assembled and stressed that it can, over a displacement range, be compressed against the force of the first spring, wherein the at least one abutment determines a minimum biasing force. 
     The impact buffer is integrated in the first or second part. The relevant first part or second part additionally includes a first sub-member and a second sub-member and the impact buffer connects the first sub-member with the second sub-member. It is thus achieved that a buffer zone able to absorb impact peaks in the energy store can be provided. 
     The aforesaid impact buffer advantageously includes a spring arrangement. This spring arrangement is biased by a second spring stressing force, which connects and holds together the first sub-member and the second sub-member. The second spring stressing force is set to a value greater than that of the first spring stressing force. The two sub-members are consequently so held together by means of the spring arrangement that they deflect only in the case of higher dynamic forces such as occur in the event of impact of the energy store on an abutment. This is advantageous, because the energy store in the normal actuating process can respond rapidly, since no damping components are effective. An impact is effectively absorbed merely in the case of impinging of the energy store on its end abutment. 
     Advantageously, one of the two first and second sub-members includes a threaded plate and the other one of the two sub-members includes an impact plate. The spring arrangement biases the impact plate with respect to the threaded plate by means of a tightening screw. This makes possible economic joining together of the two parts and the biasing force of the spring arrangement can thus be set in simple manner. The spring arrangement preferably comprises a plate spring column. This is a laminar arrangement of individual plate springs. High biasing force can thus be achieved. 
     Advantageously, the first part is connected with the connecting element and the second part is correspondingly connected with the housing of the actuator or with an actuator support. The first part includes a guide for the second part so that the second part is guided in the first part to be displaceable. 
     The first part advantageously includes a further slot, which co-operates with a guide pin of the second part. This further slot, together with the guide pin, determines the first and second, or front and rear, abutments, which abutments define the displacement range. The energy store itself can thus be simply assembled within the scope of preassembly. 
     Advantageously, the first and second parts are pivotably connected with the connecting element or with the housing of the actuator or an actuator support. The energy store thus ideally follows a movement of the connecting element or a trigger lever guiding the connecting element. It can execute required pivot movements without hindrance. 
     Overall, an electromechanical actuator with the afore-described features is suitable for effectively absorbing possible shock loads, which arise both during resetting of the actuator and during triggering of the actuator, and thus preventing damage of the actuator. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       An exemplifying embodiment with advantageous features is explained in the following by way of examples and schematic embodiments, in which: 
         FIG. 1  shows a schematic view of an elevator installation in side view, 
         FIG. 2  shows a schematic view of the elevator installation in cross-section, 
         FIG. 3  shows an arrangement with two elevator brakes and actuators, 
         FIG. 4  shows an actuator in a perspective view without cover, 
         FIG. 5  shows a plan view of an actuator in a readiness setting, 
         FIG. 6  shows a plan view of an actuator in an actuated setting, 
         FIG. 7  shows a plan view of an actuator in a restoring situation, 
         FIG. 8  shows a function view of an actuator in recoil prevention, 
         FIG. 9  shows a plan view of an actuator in buffered setting, 
         FIG. 10  shows a detail view of an energy store in unbuffered setting and 
         FIG. 11  shows a detail view of an energy store in buffered setting. 
     
    
    
     The same reference numerals are used for equivalent parts over all figures. 
     DETAILED DESCRIPTION 
       FIG. 1  shows an elevator installation  1  in an overall view. The elevator installation  1  is installed in a building and serves for transport of persons or goods within the building. The elevator installation includes an elevator car  2 , which can move upwardly and downwardly along guide rails  6 . The elevator car  2  is for that purpose provided with guide shoes  8  which guide the elevator car as accurately as possible along a predetermined travel path. The elevator car  2  is accessible from the building by way of shaft doors  12 . A drive  5  serves for driving and stopping the elevator car  2 . The drive  5  is, for example, arranged in the upper region of the building and the car  2  hangs at the drive  5  by support means  4 , for example support cables or support belts. The support means  4  are guided over the drive  5  to a counterweight  3 . The counterweight compensates for a mass proportion of the elevator car  2  so that the drive  5  for the main part merely has to compensate for an imbalance between car  2  and counterweight  3 . In the example, the drive  5  is arranged in the upper region of the building. It could obviously also be arranged at a different location in the building or in the region of the car  2  or the counterweight  3 . 
     The elevator installation  1  is controlled by an elevator control  10 . The elevator control  10  receives user requests, optimizes the operating sequence of the elevator installation and controls the drive  5 . 
     The elevator car  2  and, if required, also the counterweight  3  are additionally equipped with at least one brake suitable for safeguarding and/or retarding the elevator car  2  in the case of an unexpected movement or in the case of excess speed. In the example, two identically constructed brakes  13 ,  13 ′ are attached to the travel body  2 ,  3  on either side thereof. The elevator brakes  13 ,  13 ′ are, in the example, arranged below the car  2  and are actuable by an actuator  20  arranged between the two brakes  13 ,  13 ′. The actuator is electrically activated by a brake control  11 . This brake control  11  preferably also includes an electronic speed or travel path limiter, which monitors travel movements of the elevator car  2 . A mechanical speed limiter, such as is usually used, can accordingly be eliminated. 
       FIG. 2  shows the elevator installation of  FIG. 1  in a schematic plan view. The brake system includes the two elevator brakes  13 ,  13 ′. The two elevator brakes  13 ,  13 ′ are, as illustrated in detail in  FIG. 3 , coupled with the actuator  20  by way of adjusters  14 ,  14 ′ and connecting rods  9 ,  9 ′ so that the two elevator brakes  13 ,  13 ′ can be constrainedly actuated together. An unintended braking at one side can thus be avoided and the two elevator brakes  13 ,  13 ′ are actuable in simple manner by way of the common actuating unit  20 , which is controlled by the brake control  11 . The two elevator brakes  13 ,  13 ′ are preferably constructed identically or in mirror image and they act on the brake rails  7  arranged at the two sides of the car  2 . In the detail explanations with respect to the elevator brake only one elevator brake  13  is mentioned in the following, but the left-hand and right-hand elevator brakes are always signified. The brake rails  7  in the example are identical with the guide rails  6 . 
       FIGS. 4 and 5  show an actuator  20  in the so-called readiness setting. As readiness setting there is to be understood that the actuator retains the brakes in open setting so that the travel body, or the car or the counterweight, can be moved. The actuator is attached to an actuator support  21  or it includes the actuator support  21 . Auxiliary means  37 , which inter alia are provided for fastening a cover  24  (not illustrated in the drawings), are preferably arranged on the actuator support  21 . The actuator support  21  is provided with mounting elements  22 , which allow the actuator  20  to be so arranged at the travel body that it is provided with lateral freedom of movement. The actuator  20  can thus be arranged between two brakes  13 ,  13 ′ and can when required draw adjusters  14 ,  14 ′ of the brakes towards one another (or push them away from one another). The mounting elements  22 , for example slide pins, make lateral compensation possible. An actuator holder  23  in that case limits the lateral slide path. 
     A trigger lever  27  is arranged on the actuator support  21 . The trigger lever  27  is pivotable about a fulcrum determined by a connecting element  26 . By way of example, a connecting strap  25  is connected with the trigger lever  27  by way of the connecting element  26  and the connecting strap  25  enables connection with the brakes  13 ,  13 ′ by way of appropriate connecting rods  9 ,  9 ′. Pivoting of the trigger lever  27  thus causes pivoting of the connecting strap  25  and thereby causes the corresponding connecting rods  9 ,  9 ′ to be drawn together or pushed apart. In the example, the connecting element  26  is a shaft which is rotatably or pivotably mounted in the actuator support  21  of the actuator and to which the trigger lever  27  and the connecting strap  25  are secured. This shaft forms the fulcrum of the trigger lever  27 . An energy store  40  acts on one end of the trigger lever  27  and can introduce force into the trigger lever  27  by way of a front connecting point  35 . This force is introduced into the actuator support  21  by way of a rear connecting point  36 . The energy store  40  seeks to pivot the trigger lever  27 . In the readiness setting of the actuator  20  this is prevented by a retaining device  30 , which engages another end of the trigger lever  27  and restrains the trigger lever  27  against the force of the energy store  40 . The retaining device  30  consists of a latch  29 , which fixes a connecting point  28  of the trigger lever  27 . The latch  29  is kept in the readiness setting by an electromagnet  31  ( FIGS. 4 and 5 ). 
     When required, the brake control  11  switches the electromagnet  31  to be free of current, as is apparent from  FIG. 6 . The latch  29  can thereby be urged away from the connecting point  28  or from possible spring elements and the energy store  40  can correspondingly actuate the trigger lever and obviously the connected connecting element  26  and connecting strap  25 , etc. 
     The energy store  40  includes an impact buffer  53 . The impact buffer  53  has the purpose of absorbing or deflecting a possible shock when the energy store reaches its end abutment or the rear abutment. The construction of an exemplifying energy store  40  with impact buffer is illustrated in  FIGS. 10 and 11 . 
     In the illustrated example the energy store  40  consists of a first part  41  and a second part  42 . These two parts  41  and  42  are urged apart by a first spring  43 . The spring  43  generates the actual force of the energy store  40  for actuation of the brakes. The two parts  41 ,  42  are held together by means of a guide pin  57 . Disposed for that purpose in the first part is a slot  51  which in conjunction with the guide pin  57  integrated in the second part  42  defines a displacement range between the first part  41  and the second part  42 . If the energy store in the actuator is stressed, the trigger lever compresses the energy store and the guide pin  57  is in the vicinity of the front abutment  52   v  of the slot  51 .  FIG. 10  shows the energy store in this stressed state. If the trigger lever  27  is released, the first spring  43  relaxes or it expands the energy store and the guide pin  57  migrates in the direction of a rear abutment  52   h  in the slot  51 . If now an actuator is triggered without, for example, a brake being connected, whether it be for test or modification purposes, the guide pin impinges at high trigger speed and force at the end abutment or the rear abutment  52   h . That can to lead to destruction of the actuator. In order to avoid this the impact buffer  53  is integrated in the first part  41 . For that purpose the first part  41  includes a first sub-member  44  and a second sub-member  48 . The two sub-members are pressed together by means of a resilient body, in the example a spring arrangement  54 . This pressing together takes place by a compression force which is greater than the force of the compressed first spring  43 . If now the guide pin  57  impinges on the rear abutment  52   h  of the slot  51 —see  FIGS. 9 and 11 —when the first spring  43  is relaxed the first sub-member can move further within the scope of a spring stroke L of the spring arrangement  54  and the impact load in the actuator is thereby reduced. 
     In the embodiment, the second sub-member  48  includes a second guide tube  49 , which is slidably mounted in the second part  42  and is held by way of the guide pin  57 . The second part  42  is secured, preferably pivotably, in the actuator  20  by way of the rear connecting point  36 . The second part  42  includes a receiving region for the first spring  43 . In the embodiment the guide pin  57  and the rear connecting point are realized by the same component. Additionally disposed in the second sub-member  48  is a thread, for example in the form of a threaded plate  50 , for connection of the first sub-member  44 . 
     The first sub-member  44  similarly includes a first guide tube  58 , which is provided for connection with the trigger lever  27  and which has a corresponding receiving zone  58   a  for accepting the spring force of the spring  43 . The receiving zone  58   a  and the first guide tube  58  can obviously be of single-part or multi-part construction. The first sub-member  44  includes an impact plate  47 . The impact plate  47  is biased by way of the spring arrangement  54  with respect to the second sub-member  48  by a draw screw  55  as well as possible thrust washers  56 . Advantageously, a biasing force of the spring arrangement  54  is set by means of a spring tube  46 . The spring arrangement  54  is preferably assembled in the form of a column of plate springs. 
     If the actuator is in the actuated setting as illustrated in  FIG. 6 , the actuator can be reset by means of a resetting device  60 . The resetting device  60  includes a return lever  32 . The return lever  32  is, in the example, arranged to be pivotable about the fulcrum defined by the connecting element  26 . The return lever  32  and the trigger lever  27  are thus arranged to be pivotable about the same fulcrum and they can thus follow the same pivot radius R. The retaining device  30  together with electromagnet  31  and latch  29  is arranged on the return lever  32 . The return lever  32  is connected by way of a guide pin  63  with a return carriage  65 , which can be moved forwards and back by means of spindle drive  64 . 
     The spindle drive  64  includes a geared motor  68  which can drive a return spindle  67 . A spindle nut  66  is arranged in the return carriage  65 . The spindle nut  66  and thus the return carriage  65  are therefore moved by rotating the return spindle  67 . The resetting device  60  or the actuator  20  includes recoil prevention means or device  61  in order to protect the resetting device  60  and the connected parts from overloading. Disposed in the return carriage  65  for that purpose is a slot  62 —see  FIGS. 7 and 8 —which defines a play tolerance between return carriage  65  and return lever  32  with guide pins  63 . A counterspring  34  draws the return lever  32  towards a first end of the range of play defined by the slot  62 . The counterspring  34  is stressed by way of a counter-pin  33  arranged at the actuator support  21 . 
     For the purpose of resetting, the electromagnet  31  is now preferably activated and the spindle drive  64  moves the return lever  32 , together with the retaining device  30 , through the pivot radius R with respect to the trigger lever  27  or the latch  29  with respect to the connecting point  28 . The return lever  32  is in that case correspondingly drawn by the counterspring  34 . As soon as the retaining latch  29  has reached the connecting point  28  the connecting point  28  presses the retaining latch  29  back and the electromagnet  31  can retentively hold the latch  29 . 
     Through return of the return carriage the actuator can now be stressed in the operating setting shown in  FIG. 5 . The resetting device  60  is of sufficiently strong design in order to stress the energy store  40 . The travel paths of the return carriage  65  are obviously controlled by way of switches (not illustrated). 
     The combination of the slot  62  and the return carriage together with the counterspring  34  now forms the recoil prevention means  61  for the actuator  20 . It is a spring-loaded recoil prevention means. If in the course of resetting an external recoil force is exerted on the connecting strap  25 , the trigger arm  27  can press back the return lever  32  by way of the resetting device  60  in that—see  FIG. 8 —the guide pin  63  is displaced in the slot  62  of the return carriage  65  against the force of the counterspring  35 . This is achieved through the fact that the recoil prevention means  61  is designed to transmit force merely in a retraction direction, thus only in the direction of a force line of action, and to enable play in the other direction. The spindle drive  64  and therefore the resetting device are thus effectively protected, since external forces cannot cause overloading of the resetting device  60 . Correspondingly, connected parts and levers are also protected from overloading. 
     The illustrated embodiments can be varied by the expert. For example, use can also be made of a pneumatic device instead of the spindle drive. The recoil prevention means, which in the example is arranged by means of slot and guide pin between return lever and return carriage, could also be in the region of the fastening of the spindle drive in the actuator support. 
     In the present description the energy store  40  and the recoil prevention means or device  61  are used together in the actuator  20 . However, it is also possible to employ and use the two items independently. The energy store protected by the impact buffer can be used for numerous purposes where protection of energy store from destruction is concerned. However, the best effect is achieved by use of both items, since an actuator is thus comprehensively protected. 
     In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.
An elevator installation braking device is actuated and reset by an electromechanical actuator including an energy store, a retaining device, a resetting device and at least one connecting element for connecting the actuator to the elevator brake. The resetting device retains the connecting element, via the retaining device and counter to the action of the energy store, in a first operating position, corresponding to a standby position of the brake, or guides the actuator back into this position. The energy store acts as required, upon release of the retaining device, on the connecting element to actuate the brake and to bring it into a corresponding engagement position. The resetting device has a recoil-prevention device to relieve recoil forces. The energy store can have a stop buffer to reduce the force impact when the energy store strikes an end position.