Abstract:
A magneto-strictive scanning unit is formed through an actuation pushrod disposed and guided on an outside of a tight housing of a position sensor, in which the delicate sensor is tightly encapsulated, and components of an actuation unit can be disassembled and repaired without opening the sensor housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to German Patent Application No. 20 2008 016972.0 filed 22 Dec. 2008. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not Applicable 
     INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a scanning unit. 
     2. Description of the Related Art 
     Scanning units are being used to either determine the presence of an object at a particular position or in a particular area, or to determine the distance between two objects which can be variable. 
     Scanning units are often operated through optical or electronic methods, wherein each method has its specific pros and cons. 
     In particular when a scanning unit has to be operated under harsh environmental conditions, thus in a highly contaminated environment or in an environment loaded with abrasive solid particles under high pressure, great heat or high humidity, optical and purely electronic scanning units reach their limits, in particular since their tight long term encapsulation poses considerable problems. 
     BRIEF SUMMARY OF THE INVENTION 
     Thus, it is the object of this invention to provide a scanning unit which is very wear resistant under harsh environmental conditions in spite of simple and cost effective manufacture and which is simple to maintain and repair and which can scan in both directions of the longitudinal axis. 
     By using a magnetostrictive measuring unit, thus a magnetostrictive position sensor for the scanning unit, the position sensor can be tightly encapsulated. Also for a magnetostrictive sensor, the encoder which is an encoder magnet then, can be also disposed touch free with respect to the sensor and be completely outside of the housing of the sensor. 
     In the present case the encoder magnet, at which the actuation pushrod of the contact scanning unit, which actuation pushrod is guided parallel to the longitudinal extension of the sensor outside of the housing of the sensor longitudinally moveable in the contact scanning unit, is longitudinally fixated at the sensor in the longitudinal portion of the housing of the sensor. 
     The scanning unit either comprises only a single actuation pushrod which respectively protrudes with both ends beyond both ends of the housing and has a scanning head at each end, or it comprises two separate actuation pushrods which protrude with their outer ends supporting the scanning heads beyond the housing of the sensor and which are mounted at each other fixated in longitudinal direction with their other rear ends, so that no relative movement of the two actuation pushrods relative to one another is possible in longitudinal direction. 
     The actuation pushrod (pushrods) can be preloaded through a spring, which preferably winds as a helix-shaped spring about the actuation pushrod and which is preferably a compression spring, either into an extended position relative to the housing or also into a retracted position relative to the housing. 
     Through providing two counteracting springs, the one or both coupled actuation pushrods can also be preloaded into a defined intermediary position. 
     By loading one of the two scanning heads in longitudinal direction towards the housing, the one or both coupled actuation pushrods are moved relative to the housing of the sensor and, thus, also the encoder magnet, which is longitudinally fixed at one of the actuation pushrods. Also, when two coupled actuation pushrods are provided, preferably overall only one encoder magnet is provided overall in order to achieve an unambiguous signal. The springs are supported on one side at one of the face plates, on the other side they are supported at a respective shoulder of the actuation pushrod which can e.g. be a slid on and longitudinally fixed support bushing 
     For two actuation pushrods which are adjacent to one another in longitudinal direction and connected to one another so they are longitudinally fixed, their rear ends can either be connected to one another directly, or their rear ends are respectively connected to one another at the same support slide which is supported in a form-locked manner in longitudinal direction at the housing in that it runs e.g. in an outer groove of the housing. 
     Also, a single pass-through actuation pushrod can be fixed at such a slide in the center portion between the two face plates in order to provide an additional guide at this location. In particular, however, the encoder magnet can be disposed in such a slide. 
     The actuation pushrod in retracted state as a starting position protrudes with its one free end, where the scanning head is disposed, not at all or only slightly beyond the longitudinal extension of the housing of the position sensor and can be extended from this position along the scanning distance, wherein it is preferably preloaded into the extended position through a spring, which extends as a helical coil spring about the actuation pushrod and which is e.g. supported at an encoder magnet at the encoder magnet on the one side. 
     Preferably, the actuation pushrod is supported in bore holes of the face plates which extend from the respective longitudinal end of the position sensor in transversal direction and which extend beyond the housing of the position sensor in order to provide a support for the actuation pushrod. 
     The housing of the position sensor is preferably comprised of a circumferentially closed profile in which the position sensor is disposed in its entirety and which is closed tight by covers on the face side. 
     In one of the cover plates, a plug connector for running the measurement signals out of the sensor can be disposed. However, also running the measurement signals out via radio is possible, which facilitates a completely tight configuration of the housing of the sensor. 
     Thus, only the actuation pushrod is disposed outside of the sensor housing. However, since the actuation pushrod can be made from massive metal, for example, and also the encoder magnet mounted thereon and the spring preloading the pushrod is not very sensitive, the entire scanning unit is not even influenced by harsh environmental conditions. 
     The guide bushings are preferably configured as slide bushings and are preferably made from plastic material or brass. 
     The guides of the actuation pushrods in the face plates are preferably configured as sliding guides, and are, on the one hand, not very susceptible to wear and can, on the other hand, can be easily replaced, like all components of the actuation pushrods, without opening the housing of the position sensor. 
     For this purpose, also the face plates which protrude in transversal direction and in which the actuation pushrod is supported, are not identical with the cover plates, which complete the hollow profile to form a housing for the position sensor and also seal it. 
     The cover plates of the hollow profile are fixed in threaded openings of the profile provided for this purpose by threading in cover bolts through respective openings in the cover plates, which openings are preferably comprised of threaded grooves open to the outside, which threaded grooves are part of the profile and extend over the entire length of the profile and the bolts are threaded into them so they tap their own threads. 
     For an approximately rectangular cross section of the hollow profile, the outward open threaded grooves are preferably disposed in the outer corners. 
     In order to mount the actuation pushrod, e.g. only two each of the four respective threaded connection at each corner of each end are being used in order to fix the cover plate at the hollow profile only passing through the cover plate. 
     For this purpose, respective recesses or pass-through openings are disposed in the respective face plate at the two respective locations, in which face plate, the bolt head of the cover bolt are disposed. 
     Subsequently, the face plates are placed onto the end covers, which are already place tight onto the hollow profile and bolted down, and they are bolted to the profile through two additional cover plates, which now extend through the face plate as well as through the cover plate into the profile and which press the face plate against the cover plate and affix it. 
     Already before assembling the two face plates, the respective support bushing for the actuation pushrod is mounted therein, and the actuation pushrod is inserted with the spring preloading it. 
     This way, in case the actuation pushrod or the encoder magnet or the spring or the guide bushings are damaged, the entire actuation unit can be disengaged from the position sensor, which remains tightly encapsulated, through disengaging the face plates, so that the entire actuation unit can be repaired or maintained and reattached to the position sensor without having to open the housing of the position sensor. 
     The actuation pushrod thus does not have to be secured against rotation, when the encoder magnet is configured e.g. as a ring magnet, which also facilitates using particularly cost effective guide bushings with a circular cross section. 
     In order to affix the actuation pushrod in its retracted position for assembling the scanning unit, a fixation device can be provided between the pushrod and one of the face plates. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are subsequently described in more detail with reference to drawing figures, wherein: 
         FIG. 1  shows a scanning unit with an actuation pushrod in a perspective view; 
         FIGS. 2   a, b  show the same scanning unit in a top view and in a side view; 
         FIG. 3  shows a solution with an actuation pushrod and a support slide; 
         FIG. 4  shows a solution with an actuation pushrod with two scanning heads without support slide; 
         FIG. 5  shows a solution with an actuation pushrod with two scanning heads with support slides; 
         FIG. 6  shows the solution according to  FIG. 5  without spring preload; 
         FIG. 7  shows a solution with two actuation pushrods and support slides without springs; 
         FIG. 8  shows a solution with two actuation pushrods and support slides and internally disposed springs; and 
         FIG. 9  shows a solution with two actuation pushrods, support slides and springs disposed on the outside. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The scanning unit  1  is fixed at a first object (not shown), e.g. fixed through the fixation ear  18  at one of the face plates  7   b , and thus, so that when extending the scanning head  6   a  of the actuation pushrod  6 , it contacts the second object (not shown either), and which is to be detected with respect to its position or with respect to its mere presence. 
     The scanning unit  1  then detects the position of the actuation pushrod  6  of the actuation unit  6 ′ relative to the position sensor  2 , wherein the encoder magnet  12  which is fixed at the actuation pushrod  6  in longitudinal direction  10  generates a magneto-mechanical interference at the respective longitudinal position of the position sensor  2  through its tight housing  3  by means of a magnetic field, which magneto-mechanical interference is detected by the processing electronics of the magneto-strictive position sensor included in the housing  3 , and which is put out as electrical signals through the plug socket  17 , which is disposed in the one face side of the housing  3 . 
     The housing  3  of the position sensor  2  is thus made of a circumferentially closed hollow profile  4 , which is tightly closed at the open face sides through bolted on cover plates  5   a, b  and gaskets placed there between. 
     For this purpose, the cover plates  5   a, b  are bolted down on each side by means of two cover bolts  15   a, b , which are threaded into the threaded grooves  14   a, b  at two diagonally opposed corners through respective openings in the cover plates  5   a, b.    
     The threaded grooves  14   a, b , . . . are configured as outward open grooves in the corner portions of the profile as components of the profile cross section, thus extending over the entire length of the profile, which grooves comprise a groove shape and a groove size which facilitates to thread the cover bolts  15   a, b  into the threaded grooves  14   a, b  in a self-tapping manner. 
     Nevertheless, the threaded grooves  14   a, b  can be used in the center portion, thus remote from the thread  13 , for other purposes, e.g. for affixing the housing  3  and thus the entire scanning unit  1  at a component of the ambient, e.g. by means of clamping claws. 
     In longitudinal direction from the outside, a respective face plate  7   a, b  is placed onto the cover plate from the outside, which face plate extends in transversal direction  11  in one direction beyond the dimensions of the profile  4  and thus beyond the dimensions of the cover plates  5   a, b , wherein the longitudinal guides configured with guide sleeves  9  for the actuation pushrod  6  are disposed in the portion of the face plate extending beyond the profile  4  and of the cover plates  5   a, b.    
     The face plates  7   a, b  are fixed at the cover plates  5   a, b  and thus the hollow profile  4  by means of cover bolts  14   c, d  which are disposed in both other corners of the profile  4 , and which now extend through the end cover  7   a  or  b  and through the cover plate  5   a, b  into both other threaded grooves  15   c, d.    
     The actuation pushrod  6  extends through the two guide bushings  9  and protrudes outward from both guide bushings  9  in all its movement conditions. 
     In the retracted position, in which the scanning head  6   a  disposed at one end of the actuation pushrod  6  is most proximal to its adjacent face plate  7   b , the rear end of the actuation pushrod  6  protrudes the furthest from the other face plate  7   a , and in the most extended position in which the encoder magnet  17  is disposed most proximal to its forward face plate  7   b , the rear free end of the actuation pushrod  6  only marginally extends beyond the rear face plate  7   a.    
     Between the rear face plate  7   a  and the encoder magnet  12  mounted as a ring magnet on the outer circumference of the actuation push rod which simultaneously acts as a support bushing  21 , a spiral spring  8  is disposed which preloads the encoder magnet  12  disposed in the longitudinal extension of the housing  2 , and thus preloads the actuation pushrod  6  into the extended direction, which actuation pushrod is connected to the encoder magnet  12  in longitudinal direction  10 . 
       FIG. 3  shows a solution which also only comprises an actuation pushrod  6 , which only comprises a scanning head  6   a  at its end protruding in longitudinal direction beyond the housing  2 , wherein the rear end of the scanning head, however, ends in each movement position in the longitudinal portion of the housing  3  and is fixed there in longitudinal direction through a ball joint  22  at a slide  19 , which in turn is guided form-locked in longitudinal direction at the housing  2 , where it runs form-locked in an outer groove  20  provided on the outer circumference of the housing  2 . 
     Thus, nothing protrudes beyond the other end of the housing  2 , which improves the utility of the scanning unit. 
     The preloading by means of the helical spring  8  is facilitated in this case in that the spring  8  is disposed on the outside of the only face plate  7   b  penetrated by the actuation pushrod  6 , and is supported on the opposite side at a support bushing  21 , which is also longitudinally fixed outside of the longitudinal extension of the housing  2  on the actuation pushrod  6 . 
       FIG. 4  shows a solution which differs from the solution in  FIGS. 1 and 2 , thus with a single actuation pushrod  6  which penetrates both face plates  7   a  and  b , in two respects. 
     On the one hand, the actuation pushrod  6  comprises a respective scanning head  6   a  at both ends, which scanning head can be used for scanning, on the other hand, the encoder magnet  12  mounted in the longitudinal extension of the housing  2  is not functionally integrated with the support bushing  21 , which is mounted longitudinally fixed on the actuation push rod  6  also in the longitudinal extension of the housing  2  at another location than the encoder magnet  12  and which serves as a support for the spring  8 : 
       FIG. 5  shows a solution similar to  FIG. 4 , but with the difference that the actuation pushrods  6  passing through both face plates  7   a, b  are additionally pivotably connected in the portion between the face plates  7   a, b  to a slide  19  analogous to  FIG. 3 , thus through a ball joint  22 . Like in  FIG. 3 , also here, the encoder magnet  12  is disposed in the slide  19 , and the slide  19  is supported form-locked in an outer groove  20  of the housing  2 . 
     Furthermore, the actuation pushrod  6  is supported in this solution in a center position through two counteracting springs  8   a, b , which are respectively supported at one of the face plates  7   a, b  on its outside, and which are supported on the opposite side at one support bushing  21   a, b , which is disposed on the actuation pushrod  6  respectively outside of the face plates  7   a, b.    
       FIG. 6  shows the same configuration as  FIG. 5 , but without springs and support bushings, so that in this solution according to  FIG. 6 , a defined position of the slide  19  and the encoder magnet included therein, which can be sufficient for some applications, can only be accomplished by synchronous simultaneous loading of both scanning heads  6   a, b  in opposite direction towards each other. 
       FIGS. 7 through 9  show solutions, in which two separate actuation pushrods  6 ,  6 ′ are provided instead of a single actuation pushrod  6 , wherein each of the pushrods passes through one of the face plates  7   a, b  and supports a scanning head  6   a, b  at its outer end, while the rear ends of these two actuation pushrods  6 ,  6 ′ are coupled to one another longitudinally fixed, and thus in turn through a slide  19 , which preferably includes the encoder magnet and at which both actuation pushrods  6 ,  6 ′ are supported through ball joint  22  at their rear ends. As described, this slide  19  is supported form-locked in an outer groove  20  of the housing  2 . 
     The embodiments of the  FIGS. 7 ,  8  and  9  differ in that in the embodiment according to  FIG. 9 , the slide  19  and thus also the two actuation pushrods  6 ,  6 ′ are preloaded in a defined center position through two springs  8   a, b  acting in opposite directions to one another, which are disposed on the respective outsides of the face plates  7   a, b  as shown in  FIG. 5 , and which are embodied here as coil springs coiled around the actuation pushrods and supported at the support bushings  21   a, b  of the actuation pushrods  6 ,  6 ′. 
     This facilitates a travel range of the slide  19  over almost the entire length of the housing  2 . 
     If this is not required, the two springs  8   a, b  according to the embodiment of  FIG. 8  can also be respectively disposed at the insides of the support plates  7   a, b , which slightly limits the travel distance of the slide  19 . 
       FIG. 7 , on the other hand, shows an embodiment entirely without preloading springs analogous to  FIG. 6 . 
     REFERENCE NUMERALS AND DESIGNATIONS 
     
         
           1  scanning unit 
           2  position sensor, sensor 
           3  housing 
           4  hollow profile, profile 
           5   a, b  cover plate 
           6  actuation pushrod 
           6 ′ actuation pushrod 
           6   a  scanning head 
           7   a, b  face plate 
           8  spring 
           9  support bushing 
           10  longitudinal direction, longitudinal extension 
           11  transversal direction 
           12  encoder magnet 
           13  threaded connection 
           14   a, b  threaded groove 
           15   a, b  cover bolt 
           16  fixation device 
           17  plug socket 
           18  fixation ear 
           19  slide 
           20  outer groove 
           21   a, b  support bushing 
           22  ball joint