Patent Publication Number: US-2016230861-A1

Title: Linear Actuator Capable of Measuring Distance

Description:
NOTICE OF COPYRIGHT 
     A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to any reproduction by anyone of the patent disclosure, as it appears in the United States Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever. 
     BACKGROUND OF THE PRESENT INVENTION 
     1. Field of Invention 
     The present invention relates to linear actuators, and more particularly to a linear actuator capable of measuring distance that has the resistance scale mounted inside the actuator and kept from sight. 
     2. Description of Related Arts 
     Linear actuator has a wide range of applications in many industries. Resistance scale type linear actuator is most commonly used for precision machinery application. A resistance scale type linear actuator (or called as linear potentiometer feedback device) (as shown in  FIG. 1 ) generally comprises an actuator  10  and a resistance scale  20 . The actuator  10  (see  FIG. 2  and  FIG. 3 ) comprises a housing  101 , a power drive  102 , a connection member  103 , a screw rod  104 , a sliding block  105 , a push rod  106 , and an end cap  107 . The housing  101  is a hollow aluminum extrusion shell. The power drive  102  is mounted at one end of the housing  101  (see  FIG. 3 ). The connection member  103  is mounted inside the housing  101 . The screw rod  104  is axially accommodated in the housing  101 . The connection member  103  is connected between the power drive  102  and the screw rod  104 . The sliding block  105  is threaded onto the screw rod  104 . Further, the push rod  106  is fixedly connected to an outer wall of the sliding block  105  and extending out of the housing  101 . The end cap  107  is capped on the opposite end of the housing  101 . The resistance scale  20  comprises a casing  201 , a resistance substrate  202  and an electric brush holder  203  mounted in the casing  201 , an electric brush  2031  mounted in the electric brush holder  203  and kept in contact with the resistance substrate  202  for electric conduction, and a rod member  204  connected to one end of the electric brush holder  203  and extending out of the casing  201  and connected to the push rod  106  by a connector  30 . Further, the actuator  10  and the resistance scale  20  are fastened together with two fastening members  40 . 
     In application, the resistance scale  20  is electrically connected to a distance indicator (not shown). When the screw rod  104  is driven to rotate by the power drive  102 , the sliding block  105  is axially moved in the housing  101  in direction toward the outside to extend out the push rod  106 . At this time, the rod member  204  of the resistance scale  20  is moved outwards by the push rod  106 , causing displacement of the electric brush  2031  on the resistance substrate  202 . During movement of the electric brush  2031  on the resistance substrate  202 , the resistance value is relatively changed to provide a corresponding voltage signal that is then converted into a digital signal and indicated in the distance indicator, achieving the expected measurement. 
     Because the aforesaid resistance scale type linear actuator is comprised of an actuator  10  and a resistance scale  20  that is exposed to the outside of the actuator  10 , it occupies much installation space and has a heavy weight. Further, because this design of resistance scale type linear actuator consists of a large number of components, its manufacturing cost is high and, its installation requires much labor and time. Further, the components can loosen easily upon vibration, resulting in measurement inaccuracy. 
     SUMMARY OF THE PRESENT INVENTION 
     The present invention has been accomplished under the circumstances in view. It is one object of the present invention to provide a linear actuator capable of measuring distance, which has the advantages of simple structure, small size, inexpensive manufacturing cost and high measurement precision. 
     To achieve this and other objects of the present invention, a linear actuator comprises an actuator and a resistance scale. The actuator comprises a housing, a power drive, a connection member, a screw rod, a sliding block and a push rod. The power drive is mounted at one end of the housing. The connection member and the screw rod are axially disposed in the housing. The connection member is connected between the power drive and the screw rod. The sliding block is threaded onto the screw rod. The push rod is affixed to one side of the sliding block, and extended out of the housing. The screw rod is rotatable by the power drive. The sliding block is axially moved in the housing along the screw rod to move the push rod in or out of the housing upon rotation of the screw rod in one of two reversed directions. The resistance scale comprises a resistance substrate and an electric brush. The resistance substrate is fixedly mounted at an inner wall of the housing. The electric brush is fixedly mounted at an outer wall of the sliding block, and kept in contact with the resistance substrate. 
     Preferably, the resistance substrate is located at an inner bottom side inside the housing; the electric brush is located at a bottom side of the sliding block. 
     Preferably, the housing comprises at least two peepholes for detecting the resistance value of the resistance substrate. 
     Preferably, the linear actuator further comprises an end cap capped on an opposite end of the housing around the push rod. The end cap comprises a tubular flange extended out of the housing. The push rod extends through the tubular flange of the end cap to the outside of the housing. 
     Because the resistance scale is formed in the inside of the actuator in integrity, it will not become loose easily. Further, because the push rod and the electric brush are synchronously movable in the same axial path, the linear actuator can significantly reduce the impact of shaking, enhancing the measurement precision. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an oblique top elevational view of a resistance scale type linear actuator according to the prior art. 
         FIG. 2  is an exploded view of the resistance scale type linear actuator according to the prior art. 
         FIG. 3  is a sectional side view, in an enlarged scale, of the resistance scale type linear actuator shown in  FIG. 1 . 
         FIG. 4  is an elevational view illustrating an application status of a linear actuator in accordance with the present invention. 
         FIG. 5  is an exploded view of the linear actuator in accordance with the present invention. 
         FIG. 6  is a sectional side view of the linear actuator in accordance with the present invention. 
         FIG. 7  is a schematic operational view of the linear actuator in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 5  and  FIG. 6 , a linear actuator in accordance with the present invention is shown. The linear actuator comprises an actuator  1  and a resistance scale  2 . 
     The actuator  1  (as shown in  FIG. 5  and  FIG. 6 ) comprises a housing  11 , a power drive  12 , a connection member  13 , a screw rod  14 , a sliding block  15  and a push rod  16 . The housing  11  is a hollow aluminum extrusion shell. The power drive  12  is mounted at one end, namely, the rear end of the housing  11 . The connection member  13  is accommodated in the housing  11  near the rear end. The screw rod  14  is axially movably accommodated in the housing  11  in such a manner that the connection member  13  is connected between the power drive  12  and the screw rod  14 . In actual application, the other end of the screw rod  14  can be disposed inside the housing  11 , or partially extended out of the housing  11 . The sliding block  15  is movably disposed in the housing  11  and threaded onto the screw rod  14 . The push rod  16  has its one end affixed to the sliding block  15 , and its opposite end extending out of the housing  11 . Further, an end cap  17  is capped on an opposite end, namely, the front end of the housing  11 . The end cap  17  comprises a tubular flange  171  suspending outside the housing  11 . The push rod  16  is movably extended through the tubular flange  171  to the outside of the housing  11 . 
     The resistance scale  2  (see  FIG. 5  and  FIG. 6 ) comprises a resistance substrate  21  and an electric brush  22 . The resistance substrate  21  is affixed to an inner wall  11  A of the housing  11  (located at an inner bottom side inside the housing as shown in  FIG. 6 ). The electric brush  22  is affixed to an outer wall  15  A of the sliding block  15  (located at the bottom side of the sliding block as shown in  FIG. 6 ) and kept in contact with the resistance substrate  21 . 
     Further, the housing  11  comprises two peepholes  111  for detecting the resistance value of the resistance substrate  21 . 
     In application, the resistance scale  2  is electrically connected to a distance indicator  3  (for example, resistance meter, as shown in  FIG. 4 ). In measurement, start up the power drive  12  to rotate the screw rod  14 , moving the push rod  16  outwardly to the measuring point. At the same time, the sliding block  15  is moved axially in the housing  11  toward the outside. At this time, the electric brush  22  is moved with the sliding block  15  along the top surface of the resistance substrate  21  (see  FIG. 7 ), causing a change in the resistance value and producing a voltage signal output that is then converted into a digital signal and indicated in the distance indicator  3 , thereby achieving the expected measurement. 
     When compared to the prior art design as indicated in  FIG. 1  and  FIG. 4 , the linear actuator of the invention has the advantages of simple structure and small size, saving much installation labor and time, and thus, the cost of the linear actuator can be significantly lowered. More particularly, because the resistance scale  2  is formed in the inside of the actuator  1  in integrity, it will not become loose easily. Further, because the push rod  16  and the electric brush  22  are synchronously movable in the same axial path, the linear actuator can significantly reduce the impact of shaking, enhancing the measurement precision. 
     Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.