Abstract:
A mechanical vibration switch having a magnet connected to a bar that rotates about an axis, an inertial mass connected to the bar, a magnetic material part disposed in a predetermined spaced apart relation from the magnet, a spring, a stop, and an electrical relay mechanically actuated by the bar. The magnetic material part is adjusted parallel to the magnet such that the magnetic force varies approximately linearly with the common surface area S between the face of the magnet and the face of the magnetic material part.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present invention claims priority benefit of U.S. Provisional Patent Application No. 61/759,581 entitled “Mechanical Vibration Switch” filed on Feb. 1, 2013, which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally to vibration controls and, more specifically, to an improved vibration switch for rotary or reciprocating machinery protection. More specifically, the invention relates to a mechanical vibration switch. 
       BACKGROUND ART 
       [0003]    A mechanical vibration switch is a device that senses mechanical vibrations on various types of machinery and changes state when a threshold vibration level is reached. The purpose of the switch is to either provide an alert that the machine is vibrating unacceptably or to shut the machine down so that damage does not occur. Referring to  FIG. 1 , a prior art mechanical vibration switch  10  typically includes a small rare earth magnet  13 , a magnetic material part  16  (usually a steel plate), an inertial mass  19 , a spring  22 , and an electrical relay  25 . The magnetic material part  16  is mounted to the main switch mechanism  28 , and its position relative to the magnet  13 , in the set position, is adjustable by means of a screw or the like (not shown). The magnet  13  is mounted on a bar/lever  31  that is acted on by the spring  22 , and the lever arm  31  is also mechanically connected to the throw of the electrical relay  25 . The bar  31  may rotate about a pivot point  32  in the direction of arrow  33 . In the set position, the electrical relays  25  are in one state, either NO (normally open) or NC (normally closed), and the relays  25  change state depending on the position of the bar  31 . The bar  31  is also resting against a mechanical stop  34  in the set position. The mechanical stop  34  is also part of a sprung inertial mass mechanism. When the mechanical switch is in the set mode, the position of the magnetic material part  16  is adjusted so its distance d (gap) from the magnet  13  is such that the mechanical vibration switch  10  remains in the set position, but the magnetic part  16  is spaced a sufficient distance away from the magnet  13  so that the switch will change states when a threshold vibration level is encountered. 
         [0004]    The sprung mass  19  (M) exerts an inertial force (F) on the bar  31 . If the inertial force (F) plus the spring force F spring  become greater than the magnetic force F magnet  holding the switch in the set position, then the switch will change states. Thus, as vibration increases, the inertial force (F) increases until sufficient vibration is encountered to trip the switch. When the switch trips, the bar  31  moves the electrical relay  25  (relay throw) to the opposite position which changes the state of the contacts (relay) thus warning of the machine problem or shutting the machine down. 
         [0005]    The common surface area S of the surface on the magnetic material part  16  facing the magnet  13  remains constant and the distance d is adjusted in the direction of arrows  39  to adjust the sensititivity of the switch  10 . The major problem with prior art mechanical vibration switch designs is that the adjustment of the force required to change the state of the switch is highly nonlinear with the distance d between the magnet  13  and the magnetic material part  16 . This non-linear relation is illustrated by  FIGS. 2 and 3 .  FIG. 2  shows a plot of distance d versus F  magnet . This graph shows that the force of the magnet drops in a non-linear manner as the distance d increases. Because of this non-linear relationship, the sensitivity of traditional mechanical switches is frequently set too low to be effective in protecting rotating machinery, and particularly when the machines operate at slow speeds (i.e., &lt;6000 RPM). 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    With parenthetical reference to corresponding parts, portions or surfaces of the disclosed embodiment, merely for the purposes of illustration and not by way of limitation, the present invention provides an improved mechanical vibration switch ( 100 ). In one aspect, a mechanical vibration switch ( 100 ) includes a magnet ( 103 ) connected to a bar ( 121 ) that rotates about an axis ( 124 ), an inertial mass ( 109 ) connected to the bar ( 121 ), a magnetic material part ( 106 ) disposed in a predetermined spaced apart relation from the magnet ( 103 ), a spring ( 112 ) acting on the bar ( 121 ), a stop ( 130 ) capable of contacting the bar ( 121 ), and an electrical relay ( 115 ) mechanically actuated by the bar ( 121 ). In another aspect, the magnetic material part ( 106 ) has a cylindrical shape, and the mechanical vibration switch is designed to provide sensitivity adjustment by moving the magnetic material part ( 106 ) parallel to the magnet ( 103 ) so that a constant gap is maintained but the common surface area is adjusted. In another embodiment, the mechanical vibration switch includes a magnet ( 203 ) having an inside face defined by a spherical or curved surface ( 204 ). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic diagram of a prior art mechanical vibration switch; 
           [0008]      FIG. 2  is a plot showing the non-linear behavior of the magnetic forces vs. the distance d (gap) between the magnetic part and the magnet in a prior art vibration switch; 
           [0009]      FIG. 3  is a plot showing experimental data for the magnetic forces vs. distance d (gap) between the magnetic part and the magnet in a prior art mechanical vibration switch; 
           [0010]      FIG. 4  is a schematic diagram of the mechanical vibration switch of the present invention; 
           [0011]      FIG. 5  is a schematic diagram showing how the adjustment of the sensitivity of the improved mechanical vibration switch works by keeping the gap constant and adjusting the common surface area of the magnetic material part and the magnet; 
           [0012]      FIG. 6  is a plot showing the linear behavior of the magnetic forces vs. common surface area (S) between the magnetic part and magnet for the improved mechanical vibration switch of the present invention; 
           [0013]      FIG. 7  shows experimental data for the mechanical vibration switch of the present invention demonstrating the linear relation between the acceleration threshold and the movement of the magnetic material part by turning a threaded adjustment; and, 
           [0014]      FIG. 8  is a detailed perspective view of the major components of an alternate embodiment of the vibration switch according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0015]    At the outset, it should be clearly understood that like reference numerals are intended to identify the same parts, elements or portions consistently throughout the several drawing figures, as such parts, elements or portions may be further described or explained by the entire written specification, of which this detailed description is an integral part. The following description of embodiments is exemplary in nature and is not intended to restrict the scope of the present invention, the manner in which the various aspects of the invention may be implemented, or the applications or uses thereof. 
         [0016]    Unless otherwise indicated, the drawings are to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following descriptions, the terms “horizontal”, “vertical”, “left”, “right”, “up”, “down”, “parallel” and “perpendicular” as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightward”, “upwardly”, etc.) simply refer to the orientation of the illustrated structure as the partial drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of surface relative to its axis of elongation, or axis of rotation, as appropriate. 
         [0017]    With reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, the mechanical vibration switch  100  of the present invention, as shown in  FIG. 4  and described herein, has an improved switching mechanism that provides linearity of the force adjustment between the magnet  103  and the magnetic material part  106  (steel plate) making it possible to more accurately adjust the switch sensitivity. The mechanical vibration switch  100  consists of a small rare earth magnet  103 , a magnetic material part  106  usually a steel plate, an inertial mass  109 , a spring  112 , and an electrical relay  115 . The magnetic material part  106  (steel plate) is mounted to the main switch mechanism, and the position of the magnetic material part  106  relative to the magnet  103 , in the set position, is adjustable by means of a screw  107  or the like. The magnet  103  is mounted on a bar/lever arm  121  that is acted on by the spring  112 , and the bar  121  is also mechanically connected to the electrical relay  115 . The spring  112  shown is a coil spring however other biasing members capable of providing a force on the bar  121  may also be substituted as will be evident to those of ordinary skill in the art based on this disclosure. The lever arm  121  may rotate about a pivot point  124  in the direction of arrow  127 . In the set position, the electrical relays  115  are in one state, either NO (normally open) or NC (normally closed), and the relays change state when the switch trips. In addition to the electrical relay, other types of switches capable of changing state from NO to NC may also be used as will be evident to those or ordinary skill in the art based on this disclosure. The bar  121  is also resting against a mechanical stop  130  in the set position. The mechanical stop  130  may be part of a sprung inertial mass mechanism. When the mechanical switch is in the set mode, the position of the magnetic material part  106  relative to the magnet  103  may be adjusted to vary the common surface area S with magnet  103 , but the distance d (gap) remains constant. 
         [0018]    The sprung mass  109  (M) exerts an inertial force (F vibration ) on the bar  121  as given by Newton&#39;s 2 nd  Law of Motion, F vibration =M×A, where A is the acceleration of the switch. When the inertial force (F vibration ) plus the spring force (F spring ) becomes greater than the magnetic force (F magnet ) holding the switch in the set position, the switch changes state. Thus, as vibration increases, the inertial force (F vibration ) increases until sufficient vibration is encountered to change the state of the switch. The change occurs when the bar  121  moves the electrical relay  115  (relay throw) to the opposite position thereby changing the state of the relay  115  and warning of the machine problem or shutting the machine down. 
         [0019]    In the improved mechanical switch, for example, the magnetic material part  106  may be made in a cylindrical shape and the magnet  103  may be square. The cylindrical shape of the magnetic material part  106  provides for simple adjustment, for example, by means of rotation of a threaded portion  107  of the cylinder within a bore  108  having matching threads. Other shapes for the magnetic material part  106  having an outer surface suitable for interacting with the magnet  103  may also be used, but may require different mechanisms for advancing the magnetic material part  106  relative to the outer surface of the magnet  103 . As shown in  FIG. 5 , the cylindrical shape of the magnetic material part  106  may be oriented such that a longitudinal axis  124  going through the center of part  106  is parallel to the surface  127  of the magnet  103  and along its centerline, as illustrated by  FIG. 5 . Part  106  is also oriented such that if an imaginary plane on the end of the magnetic material part  106  closest to the magnet  103  is extended, it will intersect the magnet  103  near the edge closest to the part  106 . The movement directions of the mechanical switch sensitivity adjustment are shown by the arrows  133  in  FIG. 5  and these adjustments can be realized in many ways, as will be evident to persons of ordinary skill in the art based on this disclosure. One example for adjusting the position of the magnetic material part  106  is by adjusting the screw  107  attached or formed integrally with the magnetic material part  106 . When the adjusting screw  107  is turned, the plane  129  of the magnetic material part  106  (cylinder) moves across the magnet  103 , and the distance d (gap) between the surface of the magnetic material part (cylinder) and the surface  127  of the magnet  103  remains constant. This movement of the magnetic material part  106  parallel to the magnet  103  results in a linear adjustment of the magnetic force F magnet  vs. common surface area S of the magnetic material part  106  and magnet  103 , which is illustrated by  FIGS. 6 and 7 . 
         [0020]    The basic equation of the force between the magnet  103  and the magnetic material  106  can be simplified to the following. 
         [0000]    
       
         
           
             
               F 
               magnet 
             
             = 
             
               B 
                
               
                 ( 
                 
                   S 
                   
                     
                       d 
                       k 
                     
                     + 
                     
                       d 
                       0 
                     
                   
                 
                 ) 
               
             
           
         
       
       
         
           
             F marnet =magnetic force 
             B=flux density coefficient 
             S=common surface area 
             d=distance between magnet and plate (gap) 
             k=coefficient, usually lay in range of 1 to 2 
             d 0 =coefficient definding the magnet force with zero gap 
           
         
       
     
         [0027]    It can be seen from the equation above, that adjusting the distance (gap) d between the magnet  103  and the magnetic material part  106  is a nonlinear function, as shown on  FIG. 2  and confirmed by  FIG. 3 . Instead of adjusting the gap d, the present invention provides for adjusting the amount of common surface area S between the magnet  103  and magnetic material part  106  which has a linear relationship with the force of the magnet  103 , as illustrated by  FIG. 6  and is confirmed by  FIG. 7 . 
         [0028]    Turning to  FIG. 8 , an alternate embodiment of the present invention is shown. A magnet  203  having a curved face  204  is mounted on a bar  208 . Although the face  204  is curved in the embodiment shown, the face  204  may also be shaped in the form of a flat planar surface. An inertial mass  215  is mechanically connected to the bar  208 . A magnetic material part  206  is mounted on an adjustable mechanism  211  that carries the magnetic material part in the direction of arrows  207  to increase or decrease the common surface area S between the magnetic material part  206  and the magnet  203 . As the common surface area S is increased by moving the magnetic material part  206  so that it moves over more of the face  204  of magnet  203 , the force of the magnet F magnet  increases. The inertial mass exerts a force F vibration  in the direction shown in the figure. A spring  209  is configured such that it exerts a force F spring  in the direction shown in the figure. When the inertial force F vibration  and the spring force F spring  becomes greater than the magnetic force holding the bar  208  in the set position, the bar  208  rotates and the state of an electrical relay  223  is changed by the movement of the bar  208  causing the contacts in the electrical relay  223  to be opened or closed. A bracket  225  supports an annular collar  229  that may be fixedly attached to the bracket  225 . The spring  209  provides a force F spring  to the bar  208  through the stop  212  which moves relative to collar  229  by means of the spring force. The spring  209  biases the bar  208  in a direction opposite the force of the magnet  203 . 
         [0029]    Accordingly, the adjustment of the magnetic material part  206  relative to the magnet  203 , such that the distance d between the magnetic material part  206  and the magnet  203  remains substantially constant while the common surface area S increases or decreases, provides for linear adjustment of the sensitivity of the switch. 
         [0030]    The present invention contemplates that many changes and modifications may be made. Therefore, while an embodiment of the mechanical vibration switch has been shown and described, and a number of alternatives discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the spirit of the invention as defined and differentiated by the following claims.