Patent Publication Number: US-8531256-B2

Title: Tool and calibration machine for calibrating a thermal trip apparatus of a circuit interrupter, and improved method

Description:
BACKGROUND 
     1. Field 
     The disclosed and claimed concept relates generally to circuit interrupters and, more particularly, to an improved tool and calibration machine employed in calibrating a thermal trip apparatus of a circuit interrupter. 
     2. Related Art 
     Numerous types of circuit interrupters are known for use in diverse applications. One type of a circuit interrupter is a circuit breaker having an operating mechanism that moves the circuit breaker between an ON condition, an OFF condition, and a TRIPPED condition. Such circuit breakers typically also include a trip mechanism that causes the operating mechanism to move the circuit breaker from the ON condition to the TRIPPED condition. The trip mechanism can include any one or more of a variety of components that can trigger the operating mechanism to open a set of separable contacts in any of a variety of overcurrent and under-voltage conditions. One type of known component of a trip mechanism is a thermal trip apparatus which includes a bimetal element that becomes heated in a persistent overcurrent condition and accordingly trips the circuit breaker. 
     While such thermal trip apparatuses have been generally effective for their intended purposes, they have not been without limitation. As is generally understood in the relevant art, a bimetal element deflects in a predetermined fashion upon heating. However, due to manufacturing variations and tolerances, the thermal trip apparatus of any given circuit breaker must be calibrated during the manufacturing process. That is, each circuit breaker&#39;s thermal trip apparatus is adjusted so that it causes the circuit breaker to trip in response to a predetermined persistent overcurrent condition, by way of example. In certain circuit breakers, the calibration process has involved an inelastic (i.e., plastic) deformation of a frame within the circuit breaker upon which the bimetal element is carried. Such an inelastic deformation occurs by receiving a rectangular-shaped object into an interior region of the circuit breaker and rotating the rectangular-shaped object to engage and inelastically deform the frame until the bimetal element has moved sufficiently that it is calibrated to trigger the operating mechanism at a predetermined current level. 
     However, if the frame has been deformed beyond the calibration point, the deformation of the frame cannot be reversed without substantial reworking of the circuit breaker, with the result that an unacceptably high number of rejected circuit breakers must be discarded because they were over-deformed during the calibration operating and cannot be easily calibrated thereafter. It thus would be desirable to provide an improved system for calibrating a thermal trip apparatus of a circuit interrupter. 
     SUMMARY 
     An improved calibration machine for calibrating a thermal trip apparatus of a circuit interrupter employs a tool having an elongated shank and a pair of engagement elements. The engagement elements are engageable with a support that carried a bimetal element. The engagement elements can deform the support in opposite directions to either increase or decrease the thermal trip setting of the thermal trip apparatus. If the support is over-deformed in one direction, it can be deformed in an opposite direction to enable a circuit interrupter whose thermal trip apparatus has been deformed beyond a target thermal calibration setting to be deformed in an opposite direction to reach the target thermal calibration setting. 
     Accordingly, an aspect of the disclosed and claimed concept is to provide an improved calibration machine that employs an improved tool to perform a calibration operation on a thermal trip apparatus of a circuit interrupter. 
     Another aspect of the disclosed and claimed concept is to provide an improved method of performing such a calibration operation. 
     Another aspect of the disclosed and claimed concept is to provide an improved circuit breaker having components including a thermal trip apparatus that are capable of calibration through an inelastic deformation of a support in either of two directions and that permits the support to be returned to a calibration setting even after the support has been inelastically deformed beyond the calibration setting. 
     These and other aspects of the disclosed and claimed concept are provided by an improved method of employing a tool in calibrating a thermal trip apparatus of a circuit interrupter. The thermal trip apparatus can be generally stated as including a thermal trip element and a support upon which the thermal trip element is disposed. The tool has an elongated shank and at least a first engagement element extending from the shank in a direction generally perpendicular to the direction of elongation of the shank. The method can be generally stated as including detecting a thermal calibration setting of the thermal trip apparatus, engaging the thermal trip apparatus with the tool, deforming the support by applying one of a compressive force and a tensile force to the shank when the thermal calibration setting is higher than a target thermal calibration setting, and deforming the support by applying the other of a compressive force and a tensile force to the shank when the thermal calibration setting is lower than the target thermal calibration setting. 
     Other aspects of the disclosed and claimed concept are provided by an improved calibration machine that is structured to calibrate a thermal trip apparatus of a circuit interrupter. The thermal trip apparatus can be generally stated as including a thermal trip element and a support upon which the thermal trip element is disposed. The calibration machine can be generally stated as including a processor apparatus, an input apparatus connected, and an output apparatus. The processor apparatus can be generally stated as including a processor and a memory. The input apparatus is connected with the processor apparatus and can be generally stated as including at least a first sensor structured to detect a thermal calibration setting of the thermal trip apparatus. The output apparatus is connected with the processor apparatus and can be generally stated as including an actuator and a tool, the actuator being connected with the processor apparatus and with the tool, the tool having an elongated shank and having at least a first engagement element extending from the shank in a direction generally perpendicular to the direction of elongation of the shank. The memory has stored therein a number of routines which, when executed on the processor, cause the calibration machine to perform operations that can be generally stated as including detecting a thermal calibration setting of the thermal trip apparatus, engaging the thermal trip apparatus with the tool, deforming the support by applying one of a compressive force and a tensile force to the shank when the thermal calibration setting is higher than a target thermal calibration setting, and deforming the support by applying the other of a compressive force and a tensile force to the shank when the thermal calibration setting is lower than the target thermal calibration setting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A further understanding of the disclosed and claimed concept can be gained from the following Description when read in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic depiction of an improved calibration machine that employs an improved tool to calibrate a thermal trip apparatus of an improved circuit interrupter; 
         FIG. 2  shows the improved circuit breaker that is depicted schematically in  FIG. 1 ; 
         FIG. 3  is a depiction of the improved tool of  FIG. 1  in proximity to an enlarged portion of the circuit breaker of  FIG. 2  during an initial portion of an improved calibration operation; 
         FIG. 4  is a view similar to  FIG. 3 , except depicting a different stage of the calibration operation; 
         FIG. 5  is a view as similar to  FIGS. 3 and 4 , except depicting the tool engaged with a support of a thermal trip apparatus of the circuit breaker pursuant to a deformation force being applied to the support to increase the calibration setting of the thermal trip apparatus; 
         FIG. 6  is view similar to  FIG. 5 , except depicting an opposite deformation force being applied to the support to decrease the calibration setting of the thermal trip apparatus; and 
         FIG. 7  is a flowchart depicting certain aspects of an improved method in accordance with the disclosed and claimed concept. 
       Similar numerals refer to similar parts throughout the specification. 
     
    
    
     DESCRIPTION 
     An improved tool  4  is depicted in  FIG. 1  as being employed by a schematically-depicted improved calibration machine  8  in order to perform a calibration operation on a circuit interrupter  12 . The tool  4  can generally be described as being of a T-shaped configuration having an elongated shank  16  and a pair of engagement elements  20 A and  20 B that extend outwardly from the shank  16  in directions substantially perpendicular to the direction of elongation of the shank  16 . In the depicted exemplary embodiment, the engagement elements  20 A and  20 B extend in opposite directions away from the shank  16 , but in other embodiments the engagement elements  20 A and  20 B can have other positional relationships without departing from the present concept. The engagement elements  20 A and  20 B each have a distal engagement surface  24 A and  24 B, respectively, facing generally away from the shank  16 , and further each have a proximal engagement surface  28 A and  28 B, respectively, facing generally in a direction toward the shank  16 . 
     As can further be understood from  FIG. 1 , the calibration machine  8  includes a processor apparatus  32 , an input apparatus  36 , and an output apparatus  40  that are connected together and that are configured to perform a calibration operation on the circuit interrupter  12 . The processor apparatus  32  includes a processor  44  and a memory  48  in communication with one another. The processor  44  can be any of a wide variety of processors such as a microprocessor or other processor without limitation. The memory  48  can be any of a wide variety of storage media, whether or not removable, and can include one or more arrays of RAM, ROM, EPROM, EEPROM, FLASH, and the like without limitation. The memory  48  has stored therein a number of routines that are collectively referred to with the numeral  52  and which are executable on the processor  44  to cause the calibration machine  8  to perform various operations. The routines  52  expressly include a calibration routine  52  which causes the calibration machine  8  to perform a calibration operation on the circuit interrupter  12  that will be described in greater detail below. 
     The input apparatus  36  includes at least one sensor  54  that is configured to detect a thermal trip setting of the circuit interrupter  12 . By way of example, the sensor  52  may be configured to detect the level of current flow over time in the circuit interrupter  12  and to further detect a point at which the circuit interrupter  12  experiences a thermal trip, at which point current typically ceases to flow. The sensor  54  in conjunction with one or more of the routines  52  can thus be said to detect a thermal trip setting of the circuit interrupter  12 . Other input devices may be employed in the input apparatus  36  without departing from the present concept. 
     The output apparatus  40  of the depicted exemplary embodiment includes an actuator  56  which physically moves the tool  4  in a number of predetermined fashions. The actuator  56  is schematically depicted in  FIG. 1  but is understood to include a number of devices that can apply compressive and tensile forces to the shank  16  of the tool  4  and can also apply torques to the shank  16  to rotate the tool  4  about the direction of elongation of the shank  16 . The actuator  56  is controlled by the processor  44  in order to adjust the thermal trip setting of the circuit interrupter  12  in response to a detection of a current thermal trip setting of the circuit interrupter  12 . That is, the processor apparatus  32  and the input apparatus  36  are cooperable to detect a present thermal trip setting of the circuit interrupter, and the processor apparatus  32  is further configured to determine the extent of departure of the present thermal trip setting from a desired target thermal calibration setting. The processor apparatus  32  thus sends instructions to the actuator  56  to manipulate the tool  4  in a fashion that will be set forth in greater detail below to adjust the thermal trip setting of the circuit interrupter  12  until it reaches the desired target thermal calibration setting. 
     As can be understood from  FIG. 2 , the circuit interrupter  12  includes a line terminal  60  and a load terminal  62  through which current passes when the circuit interrupter  12  is in an ON condition. The circuit interrupter  12  typically also includes a case or other type of enclosure, although this is not illustrated herein for purposes of simplicity of disclosure. It is noted, however, that the circuit interrupter  12  is depicted as having an aperture formed in the case that enables access by the tool  4  to the interior of the circuit interrupter  12 . 
     The circuit interrupter  12  further includes a pair of separable contacts that include a movable contact  64  connected with the line terminal  60  and a stationary contact  68  connected with the load terminal  62 . The circuit interrupter  12  is depicted in  FIG. 2  as being in an OFF condition with the movable and stationary contacts  64  and  68  separated from one another. The circuit interrupter  12  additionally includes an operating mechanism  72  that is operable to move the circuit interrupter  12  among the ON condition, the OFF condition, and a TRIPPED condition. The circuit interrupter  12  further includes a trip mechanism  74  that includes a variety of systems that can trigger the operating mechanism  72  to move the circuit interrupter  12  from the ON condition to the TRIPPED condition. 
     In particular, the trip mechanism  74  advantageously includes an improved thermal trip apparatus  76  that is depicted at least in part in  FIGS. 2-6  and which includes a bimetal element  80  that is mounted on a support  82 . As is understood in the relevant art, the bimetal element  80  is configured to deflect in a predetermined fashion in response to an increase in its temperature. The support  82  typically is stationary during operation of the circuit interrupter  12 . The end of the bimetal element  80  that is opposite the support  82  is connected to a latch mechanism  84  of the operating mechanism  72  through the use of a leg  86  that extends from the latch mechanism  84  and which captures the end of the bimetal element  80 . When the bimetal element  80  deflects in its predetermined fashion in response to heating, the deflection of the end of the bimetal element  80  pulls the leg  86  to the right from the perspective of  FIG. 2 . This pivots the latch mechanism  84  which causes the operating mechanism  72  to move the circuit interrupter  12  from its ON condition to its TRIPPED condition. 
     As can further be understood from  FIG. 2 , the circuit interrupter  12  additionally includes a first conductor  88  and a second conductor  90  that are disposed at opposite sides of the bimetal element  80  and through which the current passes when the circuit interrupter  12  is in its ON condition. The first and second conductors  88  and  90  generate I 2 R heat in response to current flow through the circuit interrupter  12 , with such heat in turn heating the bimetal element  80  via radiation and convection mechanisms. In the event of a persistent high current, if the bimetal element  80  heats sufficiently, it will deflect in a clockwise direction from the perspective of  FIG. 2  and pull the leg  86  with it to release the latch mechanism  84  and move the circuit interrupter  12  from its ON condition to its TRIPPED condition. 
     As can be understood from  FIGS. 2-6 , the first conductor  88  has an opening  92  formed therein that is shaped to receive at least a portion of the tool  4 , particularly the engagement elements  20 A and  20 B, therethrough. While in the embodiment depicted herein the opening  92  is of a round shape to enable the tool  4  to be received therein in any orientation, the opening  92  in other embodiments could be of a rectangular shape or other shape as may be necessary depending upon the desired ability to accommodate the tool  4  therethrough and the acceptability of the effect on the conductive properties of the first conductor  88 . 
     As can further be seen from  FIGS. 2-6 , the thermal trip apparatus  76  has a hole  94  formed therein that is of a rectangular shape and that is sized to likewise receive a portion of the tool  4  therethrough, particularly the engagement elements  20 A and  20 B. In the depicted exemplary embodiment, the hole  94  can be said to be formed in both the bimetal element  80  and the support  82 , but the hole  94  could be otherwise configured without departing from the present concept. The thermal trip apparatus  76  can also be said to have a first surface  96  that faces generally toward the opening  92  and an opposite second surface  98  that can be said to extend generally away from the opening  92 . 
     The calibration operation can be stated to generally begin with the tool  4  being situated at the exterior of the circuit interrupter  12 , as is indicated generally in  FIG. 3 . While the tool  4  is depicted in  FIGS. 3-6  as being unconnected with the calibration machine  8 , it is understood that the calibration machine  8  will actually be connected with the tool  4 , but the calibration machine  8  is not expressly depicted in  FIGS. 3-6  for reasons on simplicity of disclosure. 
     The portion of the tool  4  that includes the engagement elements  20 A and  20 B is translated by the actuator  56  to be received through the opening  92  until the engagement elements  20 A and  20 B are situated generally between the first conductor  88  and the support  82 . In such position, the tool  4  can be rotated by the actuator  56  about the direction of elongation of the shank  16 , if needed. That is, depending upon the orientation in which the tool  4  was received through the opening  92 , such as with the engagement elements  20 A and  20 B being disposed above and below one another as is indicated generally in  FIG. 4 , a rotation of the tool about the direction of elongation of the shank  16  through an angle of about ninety degrees will orient the engagement elements  20 A and  20 B in a horizontal arrangement from the perspective of  FIGS. 3-6 . 
     In such an orientation, a compressive force can be applied by the actuator  56  to the shank  16  to cause the engagement elements  20 A and  20 B to engage the first surface  96 , as is indicated generally in  FIG. 5 . Further compressive force applied by the actuator  56  to the shank  16  and transferred to the support  82  causes the support  82  to be inelastically deformed. That is, the deformation of the support  82  can be beyond the limits of elasticity of the support  82  to cause a plastic deformation of the support  82 . Such a deformation of the support  82  to the left as is indicated generally in  FIG. 5  will raise, i.e., increase, the thermal trip setting of the thermal trip apparatus  76  since it will increase the deflection that is required of the bimetal element  80  to move the leg  86  and thus operate the latch mechanism  84 . As has been suggested elsewhere herein, the calibration operation actually would have begun with an initial test on the circuit interrupter  12  to ascertain a preliminary thermal trip setting of the thermal trip apparatus  76 , and if the calibration routine  52  determines that the preliminary thermal trip setting is too low, the calibration routine  52  may instruct the actuator  56  to apply a compressive force to the shank  16  to deform the support  82  in the fashion depicted generally in  FIG. 5  to increase the thermal trip setting. 
     On the other hand, if the calibration routine  52  determines that the thermal trip setting of the thermal trip apparatus  76  is too high, the actuator  56  can pivot the tool  4  about the direction of elongation of the shank  16 , as needed, to align the engagement elements  20 A and  20 B with the hole  94  formed in the thermal trip apparatus  76 . The shank  16  can then be translated by the actuator  56  to receive that portion of the tool  4  through the hole  94 . The tool  4  can thereafter be pivoted by the actuator  56  about the direction of elongation of the shank  16  through an angle of about ninety degrees and can thereafter apply a tensile force to the shank  16  to cause the engagement elements  20 A and  20 B to engage the second surface  98 , as is indicated generally in  FIG. 6 . Further application of such a tensile force to the shank  16  causes inelastic deformation of the support  82  in a direction generally to the right in  FIG. 6 , which has the effect of lowering, i.e., decreasing, the thermal trip setting of the thermal trip apparatus  76  by moving the end of the bimetal element  80  opposite the support  82  closer to the free end of the leg  86  or into engagement with the free end of the leg  86 . 
     While the deformations of the support  82  through engagement of the tool  4  with the support  82  (by operation of the actuator  56 ) causes inelastic, i.e., plastic, deformation of the support  82  which changes the thermal trip setting of the thermal trip apparatus  76 , it can be understood that such deformation can be reversed by applying a deformation force to the support  82  in an opposite direction. That is, if the support  82  is deformed as is indicated generally in  FIG. 5  in a fashion that increases the thermal trip setting higher than the target thermal calibration setting, the tool  4  can be moved by the actuator  56  to engage the second surface  98 , as is indicated generally in  FIG. 6 , to apply a deformation force in the opposite direction to reduce the thermal trip setting of the thermal trip apparatus  76 . In this regard, it is understood that the calibration routine  52  not only generates the initial signals to adjust the thermal trip setting by inelastically deforming the support  82 , the calibration routine  52  additionally instructs the sensor  54  to subsequently assess the adjusted thermal trip setting of the thermal trip apparatus  76  to ensure that it is within a desired range of the target thermal calibration setting. If it is not, the calibration routine  52  will instruct the actuator  56  to move the tool  4  to make further deformation engagements with the first and/or second surfaces  96  and  98  of the support  82  until the adjusted thermal trip setting of the circuit interrupter  12  is determined to be within the desired range of the target thermal calibration setting. 
     It thus can be seen that the advantageous configuration of the thermal trip apparatus  76  and the circuit interrupter  12  enable the calibration machine  8  and the tool  4  to adjust and readjust the thermal trip setting of the circuit interrupter  12  without the need to heavily rework the circuit interrupter  12  and without the need to discard circuit interrupters that have been deformed past the target thermal calibration setting. Advantageously, therefore, the circuit interrupter  12  is relatively less expensive to manufacture than previously known circuit breakers due to the avoidance of waste in the manufacturing process. Other advantages will be apparent to those of ordinary skill in the art. 
     An improved method in accordance with another aspect of the disclosed and claimed concept is depicted with a flowchart in  FIG. 7 . A method of employing the calibration machine  8  and the tool  4  can be said to begin, as at  106 , with the detecting of a thermal calibration setting of the thermal trip apparatus  76  of the circuit interrupter  12 . As a part of this operation, the calibration routine  52  will make a determination of the extent to which the thermal calibration setting needs to be increased or decreased in order to reach the target thermal calibration setting, and it will also therefore make a determination whether the distal engagement surfaces  24 A and  24 B or the proximal engagement surfaces  28 A and  28 B will be used to inelastically deform the support  82 . 
     Processing then continues, as at  110 , where the tool  4  is engaged with the thermal trip apparatus  76 . Processing can then be said to continue, as at  114 , with the deforming of the support  82  by applying a compressive force to the shank  16  when the thermal calibration setting is one of higher and lower than the target thermal calibration setting, and, as at  118 , deforming the support  82  by applying a tensile force to the shank  16  when the thermal calibration setting is the other of higher and lower than the thermal calibration setting. In the exemplary embodiment set forth herein, the compressive force is applied to the shank  16  when the thermal trip setting is lower than the target thermal calibration setting, and the distal engagement surfaces  24 A and  24 B are engaged with the support  82 . Similarly, the tensile force is applied to the shank  16  when the thermal calibration setting is higher than the target thermal calibration setting and the proximal engagement surfaces  28 A and  28 B are engaged with the second surface  98  of the thermal trip apparatus  76 . It is reiterated that if the deformation of the support  82  causes the thermal trip apparatus to be over-calibrated, i.e., too high or too low in comparison with the target thermal calibration setting, the support  82  can simply be deformed in the opposite direction to reverse the over-calibration of the thermal trip apparatus  76 , which avoids having to reject and discard circuit interrupters as was done using previously known methodologies. 
     The improved calibration machine  8  with its improved tool  4  thus can be used to calibrate the thermal trip apparatus  76  of the circuit interrupter  12 . Such calibration can be done efficiently and rapidly and without the need to discard circuit breakers that have been over-calibrated and cannot be brought back into calibration. Other advantages will be apparent to those of ordinary skill in the art. 
     While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.