Abstract:
A braking device for load carrying cars in vertical conveyor installations with elastic suspension apparatus holds fast to guiderails to prevent vertical displacements and vertical vibrations while stopped at landings. The braking device contains integrated sensors for registering the holding forces occurring between the load carrying car and the guiderails. Before travel of the car continues, the signals from these sensors enable a drive regulator to adjust via a drive unit the tensile force in the suspension apparatus carrying the car in such a manner that the braking device is relieved and can be opened without generating a jerk on the load carrying car.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a device and a method for preventing vertical displacements and vertical vibrations of the load carrying means of vertical conveyors while they are stopped at landings, achieving the desired effect by the load carrying means being held fast on its guiderails during landing stops by means of frictional engagement, this frictional engagement being released in the presence of a corresponding control command. 
     The following description relates to passenger- or freight-elevators that represent a special type of vertical conveyors. The designation of the components therefore corresponds to the technical terms of the elevator field. For example, the load carrying means is designated as elevator car or car. 
     The European patent 0 346 195 discloses an electromagnetically actuated caliper which is designed inter alia to bind the car or counterweight of an elevator to its respective guiderail by means of frictional engagement. The brake has two double-arm levers with a common joint at their mid-point whose shaft is fastened to the car or counterweight. The gripping arms of the levers are lined with brake linings and embrace the tongue of the guiderail of the car or counterweight. The opposite, driving arms of the levers are held apart by a compression spring which gives rise to the gripping force between the brake linings and the tongue of the guiderail at the other end of the levers. Concentric to the compression spring which pushes the ends apart there is a pull-type electromagnet which, when current flows through it, overcomes the force of the compression spring and thereby opens the brake. 
     The disclosed braking device is particularly intended as a holding brake for counterweights or cars of elevators driven by linear motors, and the patent claims relate mainly to the embodiment of an integral damping element to prevent switching jolts and switching noises being caused by the pull-type magnet. 
     In elevator installations with large travel heights, cars hanging on suspension means such as, for example, wire ropes or flat belts have the disadvantage that when stopping at a landing they undergo relatively large vertical displacements whose cause is the stretching or contraction of the elastic suspension means due to changes in load. Such changes in load in the car are caused by passengers entering or leaving, or by transportation equipment being put into or taken out of the car. If the vertical displacements exceed a variable limit value, the drive usually executes a compensating movement until the surfaces of the car floor and landing floor are again at the same level. Depending on the type of change in load, several such compensating procedures may be necessary during a stop at a landing. 
     Furthermore, while stopped at a landing, such elevator cars are susceptible to vertical vibrations caused by the stopping process, changes in load, or the level-compensating procedures described above. Vertical displacements and vibrations of the car can cause passengers to experience unpleasant sensations or even alarm. Moreover, if the surfaces of the car floor and hoistway door sill are not at exactly the same level, this can lead to accidents caused by passengers stumbling as they enter or leave the car. 
     The situation described can be improved by holding the elevator car fast on its guiderails by frictional engagement. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is to create a car braking device which solves the problems concerning vertical displacement and car vibrations described above without impairing the quality of ride, and particularly without causing a jerk when the brake opens for the car to continue its travel. 
     To ensure that there is no jerk when travel commences, when using a car braking device for the purpose described, the car-side suspension means (suspension ropes, suspension and driving belts, or similar elements) should be pre-tensioned to the load which will occur after the brake is opened, which is the case if a drive unit which can be regulated with respect to torque and rotational speed pre-tensions the car-side suspension means via the traction sheave each time before travel commences, so that the braking device is completely relieved before it is opened. For optimal fulfillment of this requirement the drive regulator must have suitable information concerning the load status on the car braking device. 
     Measuring the holding forces directly on the car braking device is advantageous because this makes it possible to register and compensate the holding forces actually present and because all indirect methods of relieving the brakes are subject to a number of sources of error. 
     Installation and use of the car braking device with integrated registering of the holding forces according to the invention has a number of important advantages. The first is that perfect relief of the brake before further travel commences is not effected by a pre-tensioning torque being generated by regulation of the drive unit and calculated from the torque registered when stopping and the difference in load measured during the landing stop; instead, it is effected by this torque being continuously increased by the drive unit before travel commences until a measuring bridge formed by the load-measuring sensors of the car braking device is in balance, i.e. the car braking device is perfectly relieved. With this method, deviations due to frictional effects, or resulting from errors in measuring the load in the car, and from inaccuracies in generating a torque corresponding to a calculated reference value, are ruled out. 
     Secondly, its use makes it possible to dispense with the relatively costly measurement of the load in the car, because the load in the car can be sufficiently accurately calculated from the torque on the drive unit before stopping and the change in load on the car braking device during the landing stop, the weights of the car, counterweight, and—depending on the position of the car—ropes being included in this calculation. 
     Thirdly, the car braking device according to the invention can replace the usual holding brake on the drive unit, although operation with both braking devices is possible. 
     Because the car braking device registers the holding forces in the upward and downward direction, the regulable drive unit has enough information available in all possible load situations to completely relieve the car braking device before travel continues and thereby to enable jerk-free starting. Registering the holding forces in the upward and downward direction is necessary for two reasons. If the elevator is operated with a holding brake on the drive unit, the car braking unit is loaded in opposite directions depending on whether passengers enter or leave. If operation is without a holding brake on the drive unit, the direction of load on the car braking device depends on whether the weight of the car and its momentary load is greater or less than that of the counterweight. 
     Integration of the measuring elements into the car braking device itself permits this device to be fastened onto the car in a simple, sandwich-like manner in combination with other car components, and to be electrically connected without problem. 
     Actuation of the brake levers of the car braking device by a stroke-imparting mechanism acting via a toggle mechanism has the advantage that the force of the stroke-imparting mechanism is amplified many times by simple means, and that in the braked status a continuation of the holding force of the stroke-imparting mechanism is not required. For this reason, and even taking account of power outages, stroke-imparting mechanisms can be used which have no pre-tensioned springs and operate with briefly activated closing and opening strokes such as, for example, a solenoid acting in both directions and having limited switch-on time. 
     An important advantage of this invention is that in the future, when use is made of suspension means made of synthetic fibers (e.g. aramide fiber ropes or flat belts), the problems in relation to vertical displacements and vibrations during stops at landings which are then expected to occur to a greater extent can be avoided by using the car braking device according to the invention. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which: 
     FIG. 1 is a top plan view in cross-section showing the construction of a car braking device according to the present invention, and its interaction with a guiderail; 
     FIG. 2 is a side elevation view in cross-section through the car braking device shown in FIG. 1; 
     FIG. 3 is a side elevation view in cross-section, similar to FIG. 2, through an alternate embodiment car braking device according to the present invention; 
     FIG. 4 is a schematic view of a typical elevator installation with two car braking devices according to the present invention built onto it; and 
     FIG. 5 is a top plan view of a two car braking devices according to the present invention actuated by a common stroke-imparting mechanism. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a plan view of a car braking device  1  according to the present invention. Recognizable on the left is a guiderail  2  of the sort normally used in elevator construction and on which the braking device acts. 
     The car braking device  1  consists essentially of a rectangular block-shaped casing which has fixed inside it a brake arm support  4  with two brake arm swivel bolts  5 . Each bolt  5  has a brake arm  6  rotatably mounted thereon at a brake arm hub  6 . 1 . An end of each brake arm  6  has an attached brake shoe  6 . 2  facing opposite sides of a braking surface of the guiderail  2 . Mounted on each brake shoe  6 . 2  is a brake lining  7  for frictionally engaging the guiderail  2 . A toggle mechanism  8  is connected between the arms  6  and a stroke-imparting device  9  taking the form of a solenoid, a hydraulic cylinder, or a spindle motor. A compression spring  10  is positioned to force the toggle mechanism  8  to engage the brake linings  7  with the guiderail  2  while the stroke-imparting device  9  can be actuated to release the linings from engagement. The car braking device  1  also has wire-resistance strain gages  11  mounted on the brake arm support with which the holding forces of the brake levers  6  are registered. 
     The holding effect of the car braking device  1  is achieved by the compression spring  10  acting via the toggle mechanism  8  to push the brake arms  6 , which are pivoted on the brake arm swivel bolts  5 , apart thereby pressing the brake ends of the arms together and the brake linings  7  against the running surface of the guiderail  2 . In the process, the toggle mechanism  8  greatly amplifies the force of the spring  10 . The position of the car braking device  1  shown in the drawing corresponds to the situation in which it holds the car fast on the guiderails  2  by means of frictional engagement. The car braking device  1  is released by the controllable stroke-imparting mechanism  9  overcoming the pre-tensioned force of the compression spring  10 , bringing the toggle mechanism  8  into its flexed position, thereby relieving the brake arms  6  and moving the brake linings  7  to a sufficient distance from the guiderail  2 . Not shown in the drawing is a device which uses screws to adjust the effective length of the extended toggle mechanism  8 . 
     FIG. 2 shows a vertical cross section through the car braking device  1 . Shown in the drawing are the car guiderail  2 , a baseplate  12  and a cover plate  13  of the casing  3 , the brake arm support  4  with one of the brake arm swivel bolts  5 , one of the brake arms  6  with the brake arm hub  6 . 1  and brake shoe  6 . 2 , and a cross-section through the toggle mechanism  8 , the stroke-imparting mechanism  9 , and the compression spring  10 . 
     It can be seen from FIG. 2 how registering the holding forces is effected in the car braking device  1  according to the present invention. Vertically directed holding forces on the brake shoes  6 . 2  generate via the brake ends of the brake arms  6  and the brake arm swivel bolt  5  a bending moment on a vertical section  4 . 1  of the brake arm support  4  which generates in it tensile and compressive stresses which are essentially proportional to the holding forces which occur. An electronic interpretation circuit (not shown) detects these stresses with the assistance of the metal or semiconductor wire-resistance strain gages  11  which are fastened in a suitable manner onto the aforementioned vertical section  4 . 1  and form components of an electrical bridge circuit. With this arrangement a correctly signed value for upward or downward directed holding forces can be determined, which serves as information for the control and the drive regulator regarding the load present in the car. On the other hand, by detecting when the bridge circuit is in balance, it can be very accurately determined when no more vertical holding forces are present on the closed brake levers and the car braking device can therefore be opened without generating a jerk. 
     FIG. 3 illustrates an alternative solution to the method described above of registering the holding forces acting on the car braking device  1 . Substituted for the strain gages  11  are piezoelectric pressure sensors  18  and their connecting cables  18 . 1 . Here the casing  3  contains, and has rigidly fastened to it, a metal guiderail support  14  which has two arms  15  in the form of plates each having in it two drilled holes  16  which serve as play-free guides for the brake arm swivel bolts S. The arms  15  act as a parallelogram guide for these bolts  5  which at one end are rigidly fastened with a pin  17  to the brake arm hub  6 . 1  of the brake arms  6  and at the other end are supported axially via piezoelectric pressure sensors  18  against the baseplate  12  and the cover plate  13 . If there are now vertical holding forces acting on the brake shoes  6 . 2  they are compensated by parallel, oppositely acting supporting forces acting from the base or cover plate via the pressure sensors  18  on the brake arm swivel bolt  5 . The moment on the brake arm swivel bolt is absorbed by horizontal supporting forces between the arms  15  and this bolt  5 . As a result, only the vertical components corresponding to the holding forces are transmitted to the piezoelectric pressure sensors  18 . An electronic circuit (not shown) interprets their pressure-dependent electrical characteristics and generates the information required by the elevator control and drive regulator. 
     FIG. 4 shows the application and installation in a normal elevator system of the car braking device  1  according to the present invention. An elevator hoistway  20  has installed in it vertically extending car guiderails  2 , a machine room  21  at the top containing a drive unit  22  with traction sheave  23 , an elevator car  24  carried in a car sling  25 , a counterweight  26 , and suspension means  27  which suspend and connect together the car and the counterweight and which are themselves driven by the traction sheave  23 . 
     Fastened to the car sling  25  are roller guide assemblies  28  to guide the car  24  on the car guiderails  2 , safety gears  29 , and the car braking device  1  according to the present invention. These components are constructed in such a way that by means of suitable connecting pieces they can be flanged together one below the other in the form of a sandwich and onto the car sling  25 . On very heavy cars, use of this technique makes it possible to install two or even more car braking devices one below the other. 
     FIG. 5 shows an arrangement of two car braking devices  1  in which a common compression spring  30  actuates a connection rod  32  having opposite ends connected to the toggle mechanisms  8  of both braking devices, and a common stroke-imparting device  31  fastened to the car sling acts against the pressure spring  30  to release them, as a result of which synchronous functioning is assured and one-sided braking is ruled out. 
     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.