Abstract:
A wireless breakage indicator for a shear pin having an axial bore. The indicator ( 10 ) comprises a stem ( 20 ) having a head ( 22 ) and a foot ( 24 ) at opposite ends thereof; a sleeve ( 32 ) around a portion of the stem between a first ( 28 ) and second ( 30 ) axial positions, the stem ( 20 ) and sleeve ( 32 ) adapted to be broken by the shear pin ( 12 ) in the event of its breakage; a spring ( 26 ) compressed between the head ( 22 ) of the stem ( 20 ) and a first end ( 34 ) of the sleeve ( 32 ); the foot ( 24 ) of the stem ( 20 ) being retained to the second end ( 36 ) of the sleeve ( 32 ). The breakage of the stem ( 20 ) frees the head ( 22 ) to be displaced by the spring ( 26 ) and indicate breakage of the shear pin ( 12 ). The indication can be direct, by visual inspection of the displaced head, or indirect by the displacement of the head activating a transmitter.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a national phase entry of PCT patent application no. PCT/CA2006/000769 filed on May 19, 2005 which claims priority of U.S. provisional patent application No. 60/572,128 filed on May 19, 2004, the specifications of which is are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The invention relates to the detection of a sheared component on a machinery structure, and more particularly to the indication of shear component breakage. 
     BACKGROUND OF THE INVENTION 
     Shear pins are well known in the art and are often used in applications where excessive and unusual constraints applied to a component of machinery can be dangerous for health and safety reasons, or may cause expensive machinery components to be permanently damaged. In these circumstances, a shear pin is used to provide a predetermined level of resistance to shear stress, and when that level is exceeded by an abnormal condition, the shear pin breaks at a predetermined location, warning a technician in some way and thus protecting an operator or a more expensive component. 
     In the field of hydroelectric power plants, for example, turbines are equipped with wicket gates that control the quantity of water allowed inside. The transmission of movement from a driving component to the wicket gate is done via a shear pin. In the advent of a foreign object jamming inside the gate, the excessive force transmitted to the shear pin will result in the breakage of a shear pin. The wicket gate will no longer be driven and will not be damaged. 
     Given their very nature, shear pins are expected to break in certain conditions and must thereafter be replaced. In certain applications, shear pins are disposed in hard-to-reach areas, and although the top of the shear pin are sometimes visible, it is remains difficult to tell if they are broken or not. Disassembling machinery components to verify if a shear pin is broken or not can be quite time consuming. Further, when many shear pins are provided on a piece of machinery, it is not always obvious which particular shear pin has broken and much time is lost inspecting the piece of machinery to find the broken one. Thus, there remains a need for an indication of shear pin breakage either visually accessible at the visual portion of shear pins, or accessible at a remote location from them. 
     Some detection devices have been provided in the past, but most are electrical and resistor based. Wires exiting shear pins and connecting them to a receiver circuitry are cumbersome, especially when many shear pins are used. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a shear pin breakage indication device which overcomes at least some of the shortcomings of the prior art. 
     Another object of the invention is to provide a shear pin breakage indicator which is mechanical. 
     Yet another object of the invention is to provide a visual indicator of shear pin breakage. 
     Another object of the invention is the ability to easily add to the mechanical shear pin breakage indicator an embedded electronic device to improve the efficiency of detecting a broken shear pin. 
     Still another object of the invention is to provide an indicator of shear pin breakage at a remote location by wireless transmission. 
     In accordance with one aspect, the invention provides a breakage indicator for a shear component, the indicator comprising: a head connected to a foot via a stem, the stem being adapted to be broken into a head portion and a foot portion at an axial location as a result of breakage of the shear component; an urging member adapted to displace the head towards an indication position upon breakage of the stem; and the foot being adapted to retain the head relative to the shear component via the stem; whereby breakage of the stem frees the head to be displaced into the indication position by the urging member. 
     In a more specific embodiment of the present invention, the shear component is a shear pin defining an axial bore extending there through and the shear pin includes a breakage plane transversely of the shear pin. 
     In accordance with one other aspect, the invention provides a method of indicating breakage of a shear component, comprising the steps of retaining an indicator member against an urging force urging the indicator member towards an indicator position; upon breakage of the shear component, releasing the indicator member thereby allowing the urging force to displace the indicator member into the indicator position. 
     In accordance with yet another aspect, the invention provides a wireless breakage indicator for a shear pin having an axial bore. The indicator comprises a stem having a head and a foot at opposite ends thereof; a sleeve around a portion of the stem between a first and second axial positions, the stem and sleeve adapted to be broken by the shear pin in the event of its breakage; a spring compressed between the head of the stem and a first end of the sleeve; the foot of the stem being retained to the second end of the sleeve. The breakage of the stem frees the head to be displaced by the spring and indicate breakage of the shear pin. The indication can be direct, by visual inspection of the displaced head, or indirect by the displacement of the head activating a transmitter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which: 
         FIG. 1  is a cross sectional view of a shear pin breakage indicator in accordance with an embodiment of the invention, shown inserted within a hollow shear pin; 
         FIG. 2  is a cross sectional view of the shear pin breakage indicator of  FIG. 1 , shown in indicating position, with the shear pin broken; 
         FIG. 3  is a fragmented cross sectional view of the shear pin breakage indicator of  FIG. 1 ; 
         FIG. 4  is a side elevation view of the shear pin breakage indicator of  FIG. 1 ; 
         FIG. 5  is a cross sectional view of a shear pin breakage indicator in accordance with another embodiment of the invention, with an electronic indicator, shown inserted within a hollow shear pin; 
         FIG. 6  is a cross sectional view of the shear pin breakage indicator of  FIG. 5 , shown in indicating position, with the shear pin broken; 
         FIG. 7  is a schematic view of the circuitry components of the indicator of  FIG. 5 ; 
         FIG. 8  is a schematic view of the components of the analyzer circuit for the indicator of  FIG. 5 ; and 
         FIG. 9  is a flow chart illustrating the main steps of a method of indicating breakage of a shear pin in accordance with still another embodiment of the invention. 
     
    
    
     It will be noted that throughout the appended drawings, like features are identified by like reference numerals. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with one embodiment of the invention, depicted in  FIG. 1 , the invention provides a shear pin breakage indicator  10 . The indicator  10  is inserted in a shear pin  12 . The shear pin  12  has a breakage plane  16  transverse to the axis of the pin  12 , where it is to be broken into two separate parts by a predetermined level of shear stress. The shear pin  12  also has an axial bore  14  in which the indicator  10  is inserted. Although the embodiment of the invention is illustrated with reference to a shear pin one skilled in the art will understand that the indicator can be used to indicate shearing of other shear components. 
     The indicator  10  includes a stem  20  which is inserted in the bore  14  and intersects the breakage plane  16 . The stem  20  has a head  22  at one end and a foot  24  at the other end. A sleeve  32  is concentric with a portion of the stem  20  between a spring  26  and the foot  24 , and thus covers a portion of the stem  20  extending from a first axial position  28  to a second axial position  30 . The sleeve  32  has opposed first end  34 , and second end  36 . A coil spring  26  is concentric with the stem  20 , and is compressed between the head  22  and the first end  34  of the sleeve  32  and is kept in this compressed state by the foot  22 . The spring  26  urges the head  22  out of the bore  14 . However, the stem  20  is retained in position by the foot  24  abutting against the second end  36  of the sleeve  32 . When the shear pin  12  is broken, as illustrated in  FIG. 2 , both the sleeve  32  and the stem  20  break into separate parts. The head  22  is thus released from the foot  24  and is displaced outwardly of the shear pin  12  by the spring  26 , into a position referred to as the indication position. The displacement of the head  22  is visually indicative of the breakage of the shear pin  12 . The stem  20  and sleeve  32  are made of a material that breaks easily with the shear pin  12  when breakage occurs, and which does not bend or swell by absorbing oil or humidity so that the stem  20  does not become jammed in the sleeve  32 . The preferred materials are polyamides, and most preferably, woven glass fabric epoxy laminate of NEMA FR-4 grade which is economical, easy to machine, and commonly available. 
     The sleeve  32  is used to provide easy installation of the indicator  10  in the shear pin  12 , and to allow manufacture of the indicator  10  and the pin  12  independently for applications where such a design a possible. In one alternative embodiment, the sleeve is omitted, and the indicator is directly assembled to a shear pin. The spring can then be compressed onto a shoulder of the bore at one end, for example, whereas the foot of the stem can be secured by any suitable means relative to the shear pin at the other end, like by screwing a nut onto a portion of the foot extending out of the bore. In this alternative, the stem is in direct contact with the bore. 
     Furthermore, although a coil spring  26  is used to maintain an urging force upon the head in the preferred embodiment, one skilled in the art will understand that any other suitable urging member can be used to displace the head upon breakage of the stem, such as a system in tension instead of compression, or a compressed gas, for example. 
     Turning now to  FIG. 3 , the indicator  10  is illustrated in more detail. The sleeve  32  is provided concentric to the stem  20 . A washer  38  is provided against the first end  34  of sleeve  32  and serves as an abutment member against which the spring  26  urges the head  22  away. The washer  38  serves as an intermediary between the spring  26  and the sleeve  32 . The stem  20  is preferably threaded and the head  22  and foot  24  are screwed to opposite ends thereof. The foot  24  allows the adjustment of the head  22  until it is flush with the cover  50 . The nut  40  is screwed on the threaded stem  20  between the spring  26  and the head  22 , and can be displaced along the stem to adjust the compression of the spring  26 . The nut  40  is also used as an abutment for the spring  26 . A second washer  42 , wider than the head  22 , is provided between the nut  40  and the head  22  to prevent the head from being expulsed. 
     A protective chamber  46  is defined by an annular wall  44  secured around the upper end  34  of stem  20 . The annular wall  44  and the sleeve  32  are preferably made of the same material and are glued to one another, but may also be manufactured as a single piece. The other end  48  of the annular wall is threaded and extends away from the sleeve  32 . The annular wall  44  defines chamber  46  where the spring  26 , washers  38 ,  42 , and nut  40  are enclosed. A cover  50  is screwed to the threaded end  48  of annular wall  44 . The cover  50  has an aperture  52  defined in it, in which the head  22  is engaged. The longitudinal displacement of the head  22  is guided within the aperture  52 . Preferably, the washer  42  is wider than the head  22 , and defines a ledge extending laterally from the lower portion thereof. Upon displacement of the head  22 , the movement of the head  22  is limited by the washer  42  abutting the neck portion of the cover  50  defining the aperture  52 , which keeps the head  22  from being ejected from the shear pin  12 . The head  22  is preferably of a highly visible color so that its position may be easily identified visually.  FIG. 4  illustrates the external appearance of the indicator  10 , the indicator measures approximately 15 cm in length but can be manufactured according to any suitable length. 
     In the embodiment of  FIGS. 1 through 4 , the indicator  10  is entirely mechanical and the detection of shear pin breakage is done when an operator visually inspects the head  22  and notes whether the head  22  has been displaced outwardly by the spring  26  or not. 
     An alternative embodiment with a wireless transmission indicator  110  will now be described with reference to  FIGS. 5 and 6 . Conversion of the mechanical indicator  10  to the wireless transmission indicator  110  is achieved by removing cover  50  from the threaded end  48  and replacing it by a transmitter casing  150 . 
     The transmitter casing  150  is screwed onto the upper end  48  of the annular wall  44 . The casing  150  includes a transmitter  54  and a microcontroller  58 , as well as a push button  56 . The push button  56  serves to trigger the microcontroller  58  to activate a wireless transmission of a signal from the transmitter  54 . It is disposed in the displacement axis of the head  22 . Upon breakage of the shear pin  12 , the head  22  is displaced by the spring  26  and contacts the push button  56  which activates the transmission (see  FIG. 6 ). Instead of the push button  56 , many suitable alternative contact members can be used and be activated by the displaced head, like a relay, a magnetic contact or even a proximity sensor. However, the push button  56  is preferred due to its simplicity and low cost. 
     In applications where more than one shear pin must be monitored for breakage, like in the field of hydroelectric power plants for example, a need exists for identifying the precise location of a broken shear pin. Hence, the microcontroller  58  is programmed to provide an address code associated to the location of the particular shear pin  12  upon activation of the push button  56 . Typically, there are around 10 to 40 wicket gates in an hydroelectric generator and an address coded on 8 bits (256 addresses) is usually sufficient to distinguish the different shear pins. The address code is emitted by the transmitter  54  and is then received by a receiver (see  FIG. 8 ) and is analyzed to determine the location of the broken pin. A LED on the casing  150  can be provided in combination with or instead of the transmitter to provide a visual indication of shear pin breakage. 
     The preferred circuitry is illustrated in  FIG. 7 , it includes the microcontroller  58 , the push button interrupter  56  that is mechanically activatable, the RF transmitter  54 , the LED  62 , and the power supply  60 . The microcontroller  58  is maintained in a sleep mode, which allows energy savings and prolongs the battery life, as an activation detector algorithm  68  wakes up the microcontroller  58  when stimulation is detected. The address is programmable into the microcontroller  58  and is saved in a pin ID store  70 . Preferably, the microcontroller  58  is connected to a 2.5 to 3.6 Volt power supply  60 . For example, 3 Volt, 200 mAh lithium battery should be sufficient to power the circuitry for a period of about two years. The transmitter  54  is a radio frequency (RF) transmitter and should have a low energy consumption when in sleep mode and a small sized antenna. However, one skilled in the art can select alternative modes of communication between the indicator and the receiver. 
     As illustrated in  FIG. 8 , an RF receiver  64  receives the signal from the transmitter, and communicates the data to a signal analyzer  65 . A single receiver can receive signals from several indicators. The signal analyzer  65  identifies the location of a broken shear pin by comparing the address received to a pin location store  66 . The signal analyzer  65  consequently activates an alarm generator  67 . The alarm generator triggers a relay or an electric signal and can be announced by a flashing icon on a monitor or a siren in a surveillance room, a technician observing the monitor can thus identify which shear pin(s) have failed and take appropriate action. The alarm generator could also activate a relay which stops the generator before any major problem occurs, for example. 
     The main steps of the preferred method in the electronic transmission embodiment is illustrated in  FIG. 9 . The microcontroller remains in sleep mode and relies on the push button to detect  102  the status of the stem. If the stem is broken by a broken pin, the head activates the push button and its change in status is detected. After the depression of the button by the head (see  FIG. 6 ), the microcontroller activates the transmitter to transmit  104  a breakage signal including the address code of the broken pin. If the button is not depressed, the algorithm maintains its sleep mode, waiting for a change of the status of the stem. 
     Another way to use a minimal amount of power is to use the push button as a power interrupter to the microcontroller (between the power source and the microcontroller) and to allow power transfer only when depressed. The transmission algorithm can be hardcoded in the microcontroller which can be automatically activated upon being powered and activate the signal transmission. 
     In addition, the microcontroller can be awakened by a preset periodic timer to allow monitoring of the state of the battery. After each verification of the state of the battery, a signal will be transmitted to the receiver to confirm the working condition of the electronics. An absence of signal within the predetermined time delay will mean that proper maintenance is required as soon as possible to replace the battery or the detector. Thus, in normal operation (i.e. the shear pin is not broken), the shear pin detector can transmit periodically a confirmation signal to confirm its integrity, although this is optional, and in alarm operation (i.e. the shear pin is broken), the shear pin indicator transmits an alarm signal to indicate the broken shear pin. 
     The sub steps of the method for signaling the power level of the battery include starting  106  a timer, which can occur when initializing the microcontroller for example. When the timer is determined  108  to have reached its threshold value, a signal is transmitted  112  to confirm the correct functioning status of the circuitry due to sufficient power level in the battery. The timer is then reset  106  until the threshold value is reached again. Preferably, the absence of the confirmation signal is used to determine the malfunction in the circuitry, but the power level of the battery could alternatively be checked  110  upon the timer reaching the threshold value  108 , in which case the transmitted signal could contain the power level information. This would allow the triggering of an alarm by the alarm generator that indicates the power level is low and the battery of the corresponding indicator should be replaced. Although it is illustrated in that sequence in  FIG. 9 , It is not necessary for the algorithm to check  102  the status of the stem first, and then check the timer  108  in that order, any suitable sequence can be used and both verifications can be done in parallel. 
     To prevent the risk of collision during transmission, the messages are short and repeated many times with a random delay between each transmission. Therefore, if two transmitters transmit signals at the same time, there will be very low probability that the second transmission attempt fails if the first has failed. Repetition also serves as a double-check on the validity of the signal. 
     The embodiments of the invention described above are intended to be exemplary only. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.