Piezoelectric Dosimeter Charger

This invention relates to an energy source and more particularly to a separate charging device for generating electrical energy which is to be applied to a dosimeter for subsequent use in measuring local radiation.

Electrometer type dosimeters are well known. Such apparatus, however, requires charging to predetermined value prior to being used. Thereafter when the dosimeter is exposed to surrounding radiation, the electrometer begins to discharge because of the effects of the radiation. The extent to which the electrometer is discharged provides a measure of the amount of radiation sensed by the instrument. After the dosimeter has been sufficiently discharged either from radioactivity or after an extended period of non-use, it must be recharged before being used again.

While integrated battery operated and friction type chargers are known, piezoelectric means for charging a radiation meter is disclosed in U.S. Pat. No. 2,898,472, which issued to H. E. Hollmann on Aug. 4, 1959. There two configurations are disclosed. In each instance a piezoelectric crystal element receives an impact force imparted thereto from another member which causes an internal stress to be produced within the crystal causing the required charging potential to be produced.

It is an object of the present invention, therefore, to provide a separate piezoelectric type dosimeter charger which can be used to charge various types of existing dosimeters.

It is another object of the present invention to provide a charger of the type described which can be used with dosimeters made by different manufacturers for different ranges and which have different barrel sizes and different charging switches.

It is still another object of the present invention to provide a dosimeter charger apparatus which can be used in relatively low light levels; and

Still a further object of the present invention is to provide an improved dosimeter charger which is relatively inexpensive and can be left on a shelf in an inactive state for long periods of time without detrimental effects.

Briefly, the present invention is directed to an improved dosimeter charger and includes a piezoelectric charging circuit which is contained within a housing of a generally rectangular shape. The housing includes a cover on which is mounted a spring loaded charging post and an operating handle for activating the charging circuit. The cover is easily removable and is adapted to be rotated so that the underside of the charging post can be selectively positioned to receive light therethrough from an external source, either directly from a window in the back of the housing or indirectly by means of a reflector located within the housing adjacent a second window located in the sidewalls. The charging circuit itself consists of a pair of cylindrical piezoelectric elements located end to end in a frame having a fulcrum at one end with a beam lever element located thereon in contact with one of the piezoelectric elements. The piezoelectric elements are positioned in mutually opposing polarity relationship, so that when an axial pressure is exerted thereon, a common polarity voltage is coupled from mutually opposing faces of the elements via an electrical contact and circuit lead connected to the charging post. Axial pressure is applied to the beam lever element by means of the single loop wire spring and a cam connected to the operating handle on the outside of the cover. The cam also implements a grounding switch assembly for removing residual charges.

Other objects and advantages of the presnt invention will become apparent from a detailed description of the invention when considered in light of the various drawings.

FIG. 1 is a perspective view including a cutaway section of the charger housing;

FIG. 2 is a transverse cross-sectional view of the housing shown in FIG. 1 taken along the lines 2--2 and being illustrative of the preferred embodiment of the charging unit contained therein;

FIG. 3 is a vertical cross-sectional view of the housing shown in FIG. 1 taken along the lines 3--3 and being illustrative of the light reflector contained therein adjacent a window in the sidewalls of the housing;

FIG. 4 is an axial cross-sectional view of the charging post mounted on the cover portion of the housing shown in FIG. 1;

FIG. 5 is an electromechanical diagram illustrative of the charging unit in a preliminary mode of operation prior to charging a dosimeter;

FIG. 6 is an electromechanical diagram illustrative of the charging unit during a charging mode of operation; and

FIG. 7 is an electromechanical diagram illustrative of the charging unit in a removal mode of operation.

Referring now to the drawings wherein like reference numerals refer to like elements throughout, attention is directed first to FIG. 1 wherein reference numeral 10 refers to a generally rectangular shaped housing such as included in a well known Bendix Model 880 or similar type DCPA apparatus. The housing includes a flat removable top cover 12, the underside of which is shown in FIG. 2. As shown in FIG. 2, the cover 12 includes a bifurcated edge 14 which includes a gasket member 16 which is adapted to engage the upper edge of the housing sidewalls 18. The cover 12 is held in place by means of a knurled bolt 20, which extends into the interior of the housing and engages a threaded member, not shown, attached to the inner surface of the housing's bottom wall.

The cover 12 has a charging post assembly 22 exteriorally mounted in one corner. This assembly additionally includes a pair of screw tightened gripping elements 24 and 26 which is adapted to engage and hold a conventional pocket-sized dosimeter 28 shown in place on the charging post.

The charging post 22 is placed in the corner of cover plate 12 so that light from an external source, not shown, can be directed through the dosimeter 28 during a charging operation in one of two ways, either by means of light entering a window 30 located in adjacent corners of sidewalls 18 or a window 32 located in the bottom wall 19. By loosening the bolt 20, the cover 12 can be rotated to receive light from one or the other of the windows 30 or 32. As shown in FIG. 3, the window 30 is located adjacent an angulated reflector member 34 which is secured to the bottom wall 19. Accordingly, light entering the window 30 is reflected from the surface of the reflector member 34 upward into the dosimeter 28 when the cover 12 is positioned as shown in FIG. 1. This position is particularly adapted for charging the dosimeter using a relatively strong source of light. However, when this light is insufficient, the cover 12 would be rotated so that the charging post 22 is in alignent with the window 32, whereupon the entire apparatus would be picked up and directed to whatever source of light is available. The first noted position is particularly adapted for use when the housing 10 is positioned on a flat surface, for example the top of a table or some such support.

In addition to the charging post assembly 22 located in one corner of the cover 12, there is also located a rotatable handle 36 located in the adjacent corner. The handle 36 connects to a circular cam 38 located on the underside of the cover 12 (FIG. 2) and has for its function the application of an outward force on one end of a single coil wire spring type member 40 which is bonded to one end of a beam lever element consisting of a metal plate 42. The plate element 42 contacts and holds one of a pair of piezoelectric members 44 and 46 which operate to generate a relatively high charging potential when subjected to a compressional force. The piezoelectric elements 44 and 46 are commercially available items and are comprised of a composition of lead, zirconium and titanate (P-Z-T) which is a ceramic like substance which is easily formed in a desired shape. In the subject invention, the piezoelectric material is in the form of two substantially identical cylindrical members which are axially aligned and held in position by means of a small bore 48 in the metal plate 42, an electrical coupling member 50 and an end cap 52. These parts are supported within a C shaped frame 54 having a pair of projecting end portions 56 and 58. The upper end portion 56 includes a threaded hole through which a retaining screw 60 passes for engagement with the end cap 52. The other end portion 58 includes a raised edge 62 which engages the lower surface of the plate element 42 so that a fulcrum is provided thereat whereby a force transferred to the spring 40 by means of the cam 38 is coupled to the piezoelectric elements 44 and 46 as a compressional force, the effect of which is to cause the piezoelectric elements to produce an electrical voltage across their respective end faces. By placing the two piezoelectric elements 44 and 46 so that like polarity (+) end faces exist at the coupling member 50, a relatively high charging voltage (15 kV) is produced.

The charging voltage developed by the piezoelectric elements 44 and 46 is coupled to the charging post assembly 22 by means of an electrical lead 64 which is soldered to the inner conductor 66 of the charging post assembly 22. The inner conductor 66 is also connected to an electrical lead 68 which is secured to an insulated post 70. The end of the wire 68 wound on the post 70 is adapted to make contact with a metal tip 72 on the periphery of the cam 38. These two elements act as a grounding switch in a manner to be described. Also, a second electrical lead 74 is soldered to the inner conductor 66 for acting as a switch contact for removing the residual charge on the exterior contact of the dosimeter deposited thereon during a charging procedure.

Prior to discussing the operation of the subject invention, reference is made to FIG. 4 which is generally illustrative of the charging post assembly 22. As shown in FIG. 4, the inner conductor 66 is coupled to a charging post 76 through a cylindrical outer conductor 78 which is slidable within a screw threaded sleeve 80. The sleeve is fastened to the outer surface of the cover 12 by means of a nut 82. The outer conductor 78 is spring biased upwardly by means of a pair of spring members 84 and 86 which have one end engaging an angulated sheet metal piece 88 which projects into the bore 90 and abuts a shoulder 92 on the outer conductor 78. This type of device is conventional and operates such that when the dosimeter 28 is pressed down on the assembly 22 the charging pin 94 which contacts the electrometer assembly 96 through an internal dosimeter switch including the members 97 and 98 and a compressible bellows 100 comes in contact with the charging post 76; however, the action of the springs 84 and 86 prevent damage to the dosimeter as it comes in contact with the charging post assembly 22.

Considering now the operation of the charger embodying the subject invention, reference is now made to FIG. 5. There a diagram is disclosed which is illustrative of the dosimeter 28 being pressed down on the charging post assembly 22 whereupon the charging post 76 and the charging pin 94 make contact. Also the downward motion of the inner conductor 66 causes the wire lead 74 to be lifted from the inner surface of the cover 12 and thus removing a ground connection thereat. In addition, FIG. 5 is illustrative of the fact that prior to charging, the handle 36, shown in FIG. 1, is rotated in a direction to cause the cam 38 and the pin 78 to make contact with the wire 68. This causes the coupling member 50 to be grounded through the cam 38 and handle 36, which in turn grounds the positive (+) ends of the piezoelectric elements 44 and 46. Since their negative (-) ends are connected to ground through the support frame 54, a closed circulating path is provided and any charge remaining on the elements 44 and 46 is removed.

Next, looking at FIG. 6 the dosimeter 28 is charged by rotating the handle 36 and accordingly, the cam 38 in the opposite direction from that shown in FIG. 5. This action imparts an upward force on the outer end of the wire spring 40. Since the spring 40 is not pivoted, the outer end of the pivoted plate member 42 experiences a force proportional to the force exerted by the cam 38 on the spring. This force is magnified by the lever action defined by the position of the fulcrum point 62. The upward force applied is translated via the fulcrum point 62 into a compressional force which is applied to the outer end face of piezoelectric element 44. Since both piezoelectric elements 44 and 46 are axially aligned, both elements experience an internal stress which will produce a cumulative positive charging voltage +V which is coupled to the inner conductor 66 of the charging post assembly via the circuit lead 64.

Following transfer of the charging potential to the dosimeter 28 as shown in FIG. 6, it is often necessary, following the charging of low range dosimeters, to remove the residual charge deposited by the charging process on the exterior contact 97 of the dosimeter switch, (FIG. 4) which acts to induce a charge on the electometer fiber. As this charge leaks off, the bound charge is freed and may produce spurious dosimeter readings. In order to prevent this occurrence, the external portion of the dosimeter switch is momentarily grounded immediately after charging by means of the wire element 74 which as noted above with reference to FIG. 2, is soldered on the inner conductor 66 and is adapted to contact the inner surface of the cover 12 when the charging post assembly 22 is urged back to its rest position by the bias springs 84 and 86 shown in FIG. 4. Accordingly as shown in FIG. 7, as the downward pressure of the dosimeter 28 is removed following charging, the wire element 74, being connected to the inner conductor 66, is adapted to momentarily ground the charging pin 94 via the charging post 76 which is directly connected to the inner conductor 66. The charge previously transferred to the dosimeter 28 is not affected, since in releasing the dosimeter after charging, the internal switch contact 98 of the dosimeter separates from the contact 97. The momentary grounding of the charging pin has heretofore been accomplished manually.

Thus what has been shown and described is a new and improved dosimeter charger which utilizes piezoelectric elements to provide the power source which results in a relatively simple and rugged device. Also, the housing enclosing the charging circuit includes the additional versatility of projecting light either indirectly or directly into the dosimeter to be charged depending upon the circumstances prevailing during the charging procedure.

While there has been shown and described what is at present considered to be the preferred embodiment of the subject invention, further modifications thereto will readily occur to those skilled in the art. It is not desired, therefore, that the invention be limited to the specific arrangements shown and described, but it is to be understood that all equivalents, alterations and modifications coming within the spirit and scope of the invention as defined by the following claims are herein meant to be included.