Abstract:
A devise that will increase an inductive proximity sensor&#39;s detection distance and detection position. The devise uses a housing in combination with a sensor and axially magnetized magnet and a target magnet to achieve the increased detection distance and position. The devise can be defined as universal because it allows different manufacturers and sizes of sensors to be used and calibrated. A treaded end section of the devise allows connection of standard conduit fittings.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to the field of motion detection with the use of both shielded and un-shielded inductive proximity sensors that are two or three wire design in either AC or DC voltages and more particularly to providing a means of eliminating the problem associated with the limited sensor detection distance. It should be noted that this invention is related to only inductive proximity sensors that are either shielded or un-shielded. There are other proximity sensors that are not inductive. Any reference in this application to proximity sensors pertains only to inductive proximity sensors. 
         [0002]    Inductive proximity sensors have been used for many applications requiring motion detection. Proximity sensors come in various shapes and sizes. Some are tubular while others rectangle and pancake style. It is to be noted that the foregoing sensor applications are tubular in design. These sensors, when a metal object is passed over their sensing face, will turn on or off, depending on the configuration of the sensor. The configuration of the sensor can be a normally open or normally closed. An example would be that if voltage is applied to a normally open sensor and there is not metal target over the face then the output of the sensor would be zero. Accordingly, when metal is passed over the face, the output would be the same as the voltage it is being powered with. Further, a normally closed sensor output would be the same as its input with no metal at the face and zero when metal is passed over the face. Most of industry relies on these proximity sensors to detect motion on equipment. Some of this equipment has rotating shafts, gates that open and close and many other examples. The end result from using sensors is to provide either signal (as in the case of a normally closed or normally open sensor configuration) that can be sent to a computer, indicator light, alarm or many other devises that can show if equipment being monitored is preforming correctly. 
         [0003]    The proximity sensor needs a metal target passed over the sensing face to become active. There are many ways to install sensors and to install metal targets for the sensor to detect. On rotating shafts of equipment, metal targets have been welded or attached with threaded holes. On non-rotating equipment, such as a two part gate, steel has been welded on one half of the gate and the sensor mounted on the other so as the gate closed, the sensor would detect the welded steel target. Further, as the gate opened and the two half&#39;s of the clam opened, the sensor would lose presence of the welded target and lose detection. In any case, the above examples are just a representative of possible ways target metal and sensors can be mounted. It is just an example which are used but not deemed the only way to mount such devices and how they are used to detect movement of an apparatus. 
         [0004]    The sensors used in the following description are tubular in design. Their diameter are industry standard of 8, 12, 18 and 30 mm in diameter. Their length varies. This length is not an industry standard but can be assumed to be anywhere from 1 to 4 inches. The sensing distance varies but it can be assumed that an 8 mm sensor has a much less detection distance than a 30 mm sensor. Further, these distances are usually in the order of 0.125 to 1 inch. These detection distances are based on steel as the target. Other target material such as brass, copper, aluminum, etc. decrease the sensing distance. There are other proximity sensors that have non-tubular designs which operate similarly. 
         [0005]    Proximity sensors have to be mounted and positioned according to their detection distance and position. Whereas, if a sensor had a sensing distance of 0.125 inches, it has to be mounted within 0.125 inches from the metal target to operate correctly. Also, the sensor sensing face has to be in line with the target. On a tubular sensor, the face is at one end of the tubular configuration. Obviously, if the target metal exceeds the maximum detection distance, the proximity sensor will not detect the target and thus not operate. End users of these sensors are limited in how they and the target metal are mounted. The manufacturers of sensors provide many accessories that secure the sensors when mounted so as to secure any movement of the sensor. They also provide target metal which also has to be secured. In any case, it is still the end users responsibility to mount both the sensor and the target within the parameters of sensing distance. The mounting varies according to the characteristics of the apparatus that is being monitored for movement. One example would be a rotating shaft. The target would have to be attached to the shaft and the senor mounted nearby within the detection range. A simple explanation of this process can be explained by using a common door that opens and closes. If the sensor is mounted on the door frame and the target mounted on the door it should be obvious that when the door is closed the sensor detect the target and turns on. When the door is opened the sensor loses detection of target and turns off. In any case, the detection distance must be obtained for proper operation. 
         [0006]    End users of proximity sensors are limited in mounting possibilities because of the small detection distance. In simpler examples such as a door, it would not be too difficult to stay within the detection distance parameters. In other cases, such as a rotating shaft on equipment, the mounting becomes more difficult. The majority of sensor use in industry is such that difficulties arise when trying to mount sensor and target. Staying within the confines of the sensor detection distance is something that the end user has to accomplish. Also, as noted before, the target has to pass over the sensors sensing face within the detection distance to activate the sensor. 
         [0007]    To better understand how the sensor operates, we will use an example, such as a common lead pensile. The pensile resembles an inductive proximity sensor because it is tubular in design and has an eraser on one end which also resembles the sensing face of sensors. With that in mind, if a metal target is passed close to the eraser face, it becomes active or turns on. If the target passes perpendicularly or longitudinally over the body of the pensile but not coming within the detection distance of the eraser or face, it will not turn on. The target metal also must be within the detection distance of the face or, as in the example, eraser before sensor turns on. 
         [0008]    A more technical explanation of the components that an inductive proximity sensor comprises is as follows. The present invention application provides this only for reference to better understand operation of inductive proximity sensors and that the present invention does not deem this prior art of the invention. 
         [0009]    An inductive proximity sensor has four components: the coil, oscillator, detection circuit, and output circuit. The target material, environment, and mounting restrictions all have an influence on these items and on the senor&#39;s operation, magnetic nature, and shielding. The oscillator generates a fluctuating, doughnut-shaped magnetic field around the winding of the coil, which is located in the device&#39;s sensing face. When a metal object moves into the sensor&#39;s field of detection, Eddy currents build up in the object, magnetically push back, and finally dampen the sensor&#39;s own oscillation field. The sensor&#39;s detection circuit monitors the amplitude of the oscillation and, when it becomes sufficiently damped, triggers the output circuitry. Inductive proximity sensors are designed to operate by generating an electromagnetic field and detecting the eddy current losses generated when ferrous and nonferrous metal target objects enter the field. Further, the sensor consists of a coil on a ferrite core, an oscillator, a trigger-signal level detector and an output circuit. As a metal object advances into the field, eddy currents are induced in the target. The result is a loss of energy and a smaller amplitude of oscillation. The detector circuit then recognizes a specific change in amplitude and generates a signal which will turn the solid-state output “ON” or “OFF”. 
         [0010]    As was previously noted, the proximity sensors that are used with the current invention are of either two or three wire design. In describing two wire sensors, it is necessary to also describe three wire sensors. First, two wire sensors incorporate one wire as power or feed and another as the signal. The signal has to be connected to a proper device such as a relay, computer or other indicating device for the sensor to operate. The reason for this is that the sensor needs to be connected to a device such as described to complete the circuit because all power needs a path to neutral or ground to become active. To further describe this we can use the example of a normal 110 v AC household appliance. A common receptacle has 3 slots for a cord to plug into. The third round slot is for ground but in the following example it is not discussed. One slot is high value, sometimes referred to as “hot or feed” and the other slot is neutral or the path to complete the circuit. Therefore, if only one prong of an appliance power cord was inserted into the receptacle the appliance would not work because the path would not exist. Three wire sensors incorporate one wire for “feed”, one wire for neutral or “return” and one wire as the signal. The importance of offering this two wire capability is that many end users already have two wire proximity sensors installed and a two wire proximity sensor replacement eliminates the end user to install another wire as needed in a three wire proximity sensor. The present invention provides the end user the option to use a two wire inductive proximity sensor and also increase its detection distance and position. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1  is a side and upright view of the devise that shows all the elements combined that are needed to create the current invention. All elements are within the main housing  2  except for target  4  which is to be mounted as the target.  FIG. 1  also shows sensor  1  can detect the presence of target  4  at its face end. 
           [0012]      FIG. 2  is a top view of the devise in combination but not showing target  4  as in  FIG. 1 . Dimension  11  shows minimal clearance. 
           [0013]      FIG. 3  is a side and horizontal view that is identical to  FIG. 1  except that element  4  is positioned laterally unlike  FIG. 1 .  FIG. 3  shows that the devise will operate even though element  4  is not positioned at the face end of element  1 . 
           [0014]      FIG. 4  illustrates sensing distance differences between the current invention and a inductive proximity sensor alone. Element  13 , is a target  4  as shown in  FIG. 1 . Top drawing  17 , which is the current invention, shows the many different positions the devise will detect the target and element  14  shows the distance in inches of detection. Bottom drawing  18  shows only a sensor without the current invention. It can be seen that there is only one detection position and the distance is greatly reduced. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Detailed description of the present invention are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriate detailed system, structure or manner. 
         [0016]    Referring to  FIG. 1 , the present invention will be described. Housing  2  can be seen to comprise all items that when assembled make-up the complete apparatus. It is a machined non-metallic material such as plastic, nylon, fiberglass or any other non-metallic material. Housing  2  is shown on  FIG. 2 , which is a top view of  FIG. 1 . Hole  6  is a threaded bore for sensor  1 . Hole  12  is a machined thread size of ½ inch NPT. This thread is slightly larger than  6  and allows the current invention to be connected to a standard conduit connector. In the assembly process of the current invention, sensor  1  is threaded into hole  6  and because threaded hole  12  is a larger hole, sensor  1  is inserted past threaded hole  12  till it meets the threads in hole  6 . Hole  6  is machined with threads to match sensor  1 . Sensor  1  then is threaded into housing  2  and positioned correctly. It is important to note that different manufacturers of sensors will be positioned at different locations within housing  1 . Therefore, by turning the sensor in the threads, the correct position can be attained. A better understand this procedure is as follows. When assembling a complete apparatus, all items are within or about the housing  2 . Cable  8  is connected to a pilot light for visual indication. Target Magnet  4  is positioned at approximately 3 to 4 inches from the face of sensor  1 . Sensor  1  is then adjusted within hole  6  in housing  2  till the pilot light turns on. Then, target  4  is removed to assure the pilot light turns off. Target  4  is then moved back to the original position. If the pilot light comes on, the process of positioning is complete and set screw  3  is tightened to prevent sensor  1  to move, thus assuring the assembled current invention is calibrated. The 3 to 4 inch distance referred to is just an average distance. Some sensors may meet and exceed this distance while others may not. Therefore, the 3 to 4 inch distance referred to cannot be an exact distance, although in most cases, it can be an average. 
         [0017]    Turning now to hole  10  on  FIG. 1 , the threaded bore is machined for the thread size of set screw  3 . Hole  10  is machined completely through the body of housing  2  and into the bore of hole  6 . Therefore, when sensor  1  is inserted into housing  2  and calibrated, and set screw  3  is threaded into hole  10 , set screw  3  will come in contact with sensor  1  and lock sensor  1  in place with housing  2 . Hole  10  can only be a threaded bore and set screw  3  can only be a screw with machined threads. The thread size hole  10  depends only on the thread size of set screw  3 . As was mentioned previously, sensor  1  can have different diameters and different thread sizes. Further, since the present invention will operate correctly with various diameters of inductive proximity sensors, it is obvious that hole  6  will be machined for these different diameters of sensor  1 . 
         [0018]    In  FIG. 1 , hole  9  is shown as a hole completely through the length of Item  2 . This is a straight hole without threads. The purpose of this hole is so that magnet  7 , can be press fit into hole  9 . The diameter of the hole  9  is slightly smaller than magnet  7 . The purpose of drilling hole  9  smaller than magnet  7  is to create a press fit for magnet  7 . In the process of assembling, magnet  7  is pressed into hole  9  throughout the length of housing  2 . 
         [0019]    Further on  FIG. 1 , target  4  is shown as the target magnet. Target  4  is an axially magnetized magnet. Target  4  is not included within the assembled apparatus but rather a separate entity that is to be placed on the member of equipment that is being monitored for motion detection. Item  4  is needed for the invention operation and not connected internally to Item  2 . To further clarify it should be obvious that Item  2  in its completed form contains Items  1 ,  3 , and  7 . Also, housing  2  needs to be machined for these items. Therefore, holes  6 ,  10  and  9  are the machined bores either with machined threads or straight bore. Cable  8  is only the cable from sensor  1 . 
         [0020]    In reference to target  4 , it can be seen in  FIG. 1  to be positioned at the face or detection area of Item  1 . It should be noted that the current invention uses an target  4  that is ⅞″ in diameter by 1″ long axially magnetized magnet. Thus, in the foregoing examples of detection distance, it is to be understood that any reference to detecting distances are based on Item  4  having these dimensions. The target  4  dimensions are being used for reference to show how the current invention creates a longer detection distance. The current invention can use different sizes of target  4  to accommodate different applications for the end user and will effect detection distance. 
         [0021]    In this example seen on  FIG. 1 , sensor  1  would detect target  4  and “turn on” or become active. The distance between target magnet Item  4  and Item  1  face is referred to as “detection distance”. If a standard inductive proximity sensor without the current invention was used, this distance would be a nominal distance as per the specifications of the sensor. As stated earlier, this distance is in the range of 0.125 to 1 inch. With the standard inductive proximity sensor incorporated within the current invention, this distance is increased to approximately 3.5 inches based on the size of target  4 . Because target  4  may vary in size to the application of the end user, the current invention&#39;s detection distance can vary but in any case, it greatly increases detection distance over a standard inductive proximity sensor used without the current invention. 
         [0022]    In  FIG. 3  we can see target  4  is now positioned on the side of the current invention and not at the face as was seen in  FIG. 1 . As long as the distance is within the approximate 3.5 inches, the proximity sensor incorporated within the current invention will become active or “turn on”. Also, it should be understood that sensor  1  will become active as long as target  4 , being within the detection distance, is placed other than at the face of sensor  1 .  FIG. 4  shows  13  as different locations of target  4 . The blocks A, B, C, D and E represent target  4 . Sensor  1  will become active if Item  4  is placed anywhere between Blocks A thru E within the detection distance. This is especially helpful in applications that do not permit direct alignment between target  4  and the face of sensor  1 . It should be understood that  FIG. 4  is only a representative showing multiple points that target  4  can activate sensor  1 . 
         [0023]      FIG. 2 , which is an end view. Dimension  11  shows the distance between hole  6  and hole  9 . As discussed previously, hole  6  is a threaded bore. Therefore, hole  9  straight bore needs to be as close as possible to hole  6  without interfering with the finished machined threads of hole  6 . The actual placement of hole  9  cannot be defined in dimension of placement on housing  2  because of the various diameter sizes of sensor  1  that could installed. Of course, the dimension of hole  6  depends on the dimension of sensor  1 . In any case, hole  9  and hole  6  need to be as close as possible without interfering with each ones finished machining. 
         [0024]      FIG. 4  will give a comparison of a common inductive proximity sensor and the current invention. Reference  17  shows the current invention fully assembled with all the components. Reference  13  depicts target  4  in the various positions that sensor  1  can detect target  4  presence. Also, dimension  14  shows the detecting distance in inches. Reference  18  shows just a normal sensor without the current invention. Reference  13  which is target  4  is shown in the only position where a sensor without the current invention can detect its presence. Dimension  16  shows in inches the detecting distance. 
       SUMMARY OF THE INVENTION 
       [0025]    The primary object of the invention is to provide an apparatus that extends the detection distance of inductive proximity sensors. 
         [0026]    Another object of the invention is to provide an apparatus that extends the detection distance of inductive proximity sensors of various dimensions. 
         [0027]    Another object of the invention is to provide an apparatus that extends the detection distance of two wire inductive proximity sensors. 
         [0028]    Another object of the invention is to provide a magnet that is used as a target for the inductive proximity sensor within the apparatus. 
         [0029]    Another object of the invention is to provide an apparatus that increases an inductive proximity sensor&#39;s sensing area 
         [0030]    Another object is to provide machined threads in the housing so that different brands of sensors to be properly adjusted 
         [0031]    Another object of the invention is to provide an apparatus that does not limit detection to one position 
         [0032]    Another object of the invention is to provide an apparatus that can be connected to an industry standard conduit connector 
         [0033]    Another object of the invention is to provide an apparatus that can use either two or three wire inductive proximity sensors