Abstract:
A displacement measuring appparatus is small in size and hence capable of avoiding interference with other units and further has its measurement accuracy hardly deteriorated. There are disposed pulleys for movement with respect to the body of the appartus and there is disposed an energizing means such that the pulleys are subjected to the energizing force. A wire is passed around the pulleys. When the wire is subjected to a pulling force, the pulleys are moved against the energizing force of the energizing means.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an apparatus for measuring displacement by utilizing a wire. 
     RELATED ARTS 
     Conventionally, as an apparatus for measuring a displacement along the stroke of a cylinder, there is known an apparatus that uses an encoder and a wire taken up by a coil spring. 
     The wire is taken up by a pulley constituting a take up portion. The pulley is energized by the coil spring in the direction in which the wire is taken up. A displacement along the stroke of the cylinder is measured by the direction and amount of rotation of the pulley. 
     There is, however, a demerit with the use of the conventional displacement measuring apparatus that the size of the pulley around its axis becomes large. Therefore, there has been a danger that the apparatus becomes larger according as the measured distance is increased and it interferes with other units. 
     Further, there has been such a problem that a coil spring is not durable, i.e., when it is expanded and contracted repeatedly, its elasticity becomes poor resulting in deterioration in the measurement accuracy. 
     When the measurement is carried out only by the use of an encoder, it has been difficult for a conventional apparatus to secure improved accuracy in measuring the distance. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to provide a displacement measuring apparatus smaller in size so that its interference with other units is avoided. 
     It is another object of the present invention to provide a measuring apparatus of which the measurement accuracy does not deteriorate easily. 
     A displacement measuring apparatus according to the invention is an apparatus for measuring displacement by utilizing a wire. There is movably disposed a pulley. There is disposed an energizing means such that the pulley is moved under the energizing force. A wire is passed around the pulley. When the wire is let in or let out, the pulley is moved against the energizing force of the energizing means. 
     A linear sensor may be disposed in the displacement measuring apparatus so that the let out amount or let in amount of the wire is measured by the linear sensor. 
     An encoder may be disposed in the above displacement measuring apparatus so that the let out amount or let in amount of the wire may also be measured by the encoder. 
     In the displacement measuring apparatus according to the invention, there is movably disposed a pulley in the body of the apparatus. It is preferred that a plurality of pulleys are used as a unit. There is disposed an energizing means (for example a spring) such that the pulleys are moved under the energizing force. A wire is passed around the pulleys. When the wire is led into or taken out of the body of the apparatus, the pulleys are moved against the energizing force of the energizing means. 
     Preferably, there is provided a linear sensor in the displacement measuring apparatus such that the let out amount or let in amount of the wire is measured by the linear sensor. 
     More preferably, there is disposed an encoder in the displacement measuring apparatus provided with the linear sensor so that the let out amount or let in amount of the wire is measured not only by the linear sensor but also by the encoder. 
     The displacement measuring apparatus configured as described above can be used as a displacement measuring apparatus of a cylinder used in a heavy machine such as a shovel-car. 
     In the above described case, it is possible that a linear displacement of the pulleys in the body is measured with the linear sensor to obtain the let out amount of the wire as a coarse measurement and the angle of rotation of the encoder is measured as a fine measurement. Thus, it is preferred that the two measurements with the encoder and the linear sensor be combined. 
     In measuring a linear displacement by means of the linear sensor, it is preferred, in terms of durability and cost, to carry out the measurement utilizing changes in the resistance value with the use of a conducting plastic member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an external view of a displacement measuring apparatus according to the invention. 
     FIG. 2 is a diagram schematically showing the displacement measuring apparatus of the invention. 
     FIG. 3 is a sectional view of the displacement measuring apparatus shown in FIG. 1 in the vertical direction. 
     FIG. 4 is a view of the displacement measuring apparatus in the direction of the arrows A—A in FIG.  3 . 
     FIG. 5 is a sectional view of the displacement measuring apparatus shown in FIG. 1 in the horizontal direction. 
     FIG. 6 is a diagram showing a shovel-car (heavy machine) on which the displacement measuring apparatus of the invention is installed. 
     FIG. 7 is a diagram schematically showing a mechanism for transmitting the let out amount or let in amount of the wire to the encoder according to another embodiment. 
     FIG. 8 is a view partly showing an enlarged timing belt. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described with reference to the accompanying drawings. 
     FIG. 1 is a view showing an external appearance of the displacement measuring apparatus according to an embodiment of the invention. 
     The displacement measuring apparatus  10  is capable of measuring the amount of the wire  12  led into or taken out of the body of the apparatus. The measured amount of the wire  12  led into or taken out of the body of the apparatus can be converted into an electrical signal. The measured value converted into the electrical signal is transmitted to another apparatus through a cable  14 . 
     Fixing belts  16  are used for fixing the displacement measuring apparatus  10  onto another apparatus. 
     FIG. 2 is a schematic diagram of the displacement measuring apparatus  10 . 
     The displacement measuring apparatus  10  is provided with transmission pulleys  18 ,  20 , an encoder  22 , fixed pulleys  24 ,  26 ,  28 , movable pulleys  30 ,  32 ,  34 ,  36 , and a linear sensor (line sensor)  38 . Further, a common wire  12  is passed around all the above elements. 
     The transmission pulleys  18  and  20  are capable of transmitting the wire  12  to other elements. The encoder  22  allows measurement to be made by its amount of rotation. The fixed pulleys  24 ,  26 , and  28  are fixed to the body of the displacement measuring apparatus  10 . 
     The movable pulleys  30 ,  32 ,  34 , and  36  are movable in the directions of the arrowheads indicated in FIG.  2 . The linear sensor  38  is disposed between the movable pulleys and the fixed pulleys. The linear sensor allows the movement (displacement) of the movable pulleys  30 ,  32 ,  34 , and  36  in the direction X to be measured by a change in the resistance value. 
     FIG. 3 is a sectional view of the displacement measuring apparatus of FIG. 1 in the vertical direction. 
     The wire  12  is allowed to pass through the led-out  40  and pass through the clean region  42 . In the clean region  42 , the wire  12  can be made clean of foreign objects and mud attached thereto. The wire  12  can also be coated with a resin or the like so that a clogging is prevented. Scraping the foreign matters off the rope can also be achieved by an O-ring made of a resin or the like. As the wire  12 , that having a diameter of 1.5 mm, the wire being 1.0 mm and the coating being 0.5 mm, can be used. 
     Further, the displacement measuring apparatus  10  may be provided with a sealed oil reservoir so that moisture is removed. Thereby, the apparatus is rendered more maintenance-free than before. 
     FIG. 4 is a view in the direction of the arrows A—A in FIG.  3 . 
     The wire  12  passed through the clean region  42  reaches the transmission pulley  20  through the transmission pulley  18 . The wire  12  arrived at the transmission pulley  20  is passed around the encoder  22 . 
     FIG. 5 is a sectional view in the horizontal direction of the displacement measuring apparatus shown in FIG.  1 . 
     The wire  12  passed around the encoder  22  is passed around the pulley  30 . The wire  12  passed around the pulley  30  is passed around the fixed pulley  24 . The wire  12  passed around the fixed pulley  24  is passed around the movable pulley  32 . The wire  12  passed around the movable pulley  32  is passed around the fixed pulley  26 . The wire  12  passed around the fixed pulley  26  is passed around the movable pulley  34 . The wire  12  passed around the movable pulley  34  is passed around the fixed pulley  28 . The wire  12  passed around the fixed pulley  28  is passed around the movable pulley  36 . The wire  12  passed around the movable pulley  36  is fixed at its one end to a pulley supporting member  44 . 
     The movable pulleys  30 ,  32 ,  34 , and  36  are rotatably supported by a pulley energizing portion  45  provided on the pulley supporting member  44 . The pulley supporting member  44  is capable of moving in the directions of the arrowheads X in FIG. 5 along a guide  48 . The fixed pulley  24 ,  26 , and  28  are rotatably supported by a fixing member  46 . 
     As shown in FIG. 3, there is disposed a spring  50  between the pulley supporting member  44  and the fixing member  46  so that the movable pulleys  30 ,  32 ,  34 , and  36  are given an energizing force through the pulley supporting member  44  (the spring  50  is not shown in FIG.  2  and FIG. 4 to simplify the illustration). The spring  50  is an example of energizing means. 
     Now the operation will be described. 
     When the other end of the wire  12  is subjected to a pulling force, the wire  12  is activated to move the pulley supporting member  44 . With the movement of the pulley supporting member  44 , the movable pulleys  30 ,  32 ,  34 , and  36  also move. Here, since the shifted amount or displacement of each of the movable pulleys  30 ,  32 ,  34 , and  36  is small as compared with the let out amount of the wire  12 , durability of the energizing portion  45  for energizing the movable pulleys  30 ,  32 ,  34 , and  36  and the pulley supporting member  44  is improved. 
     Now, referring to FIG.  2  and FIG. 3, the method of measuring the let out amount of the wire will be described. 
     As described above, when the wire  12  is subjected to a pulling force, the wire  12  is led out of the measuring apparatus  10  through the led-out  40 . The tension to the wire  12  is transmitted through the pulleys so that the pulley supporting member  44  is moved in the directions of the arrowheads in FIG. 3 against the energizing force of the spring  50 . The linear sensor  38  detects a change in the resistance value so that the shifted amount of the pulley supporting member  44  is detected. By the measurement of the shifted amount of the pulley supporting member  44 , the let out amount of the wire  12  with respect to the body of the apparatus  10  can be measured. In some case, the encoder  22  may be used instead of the linear sensor  38  to measure the let out amount of the wire  12 . 
     In the displacement measuring apparatus of the invention, the encoder  22  for making incremental measurement may be used in addition to the linear sensor  38  which makes absolute measurement, so that the let out amount of the wire  12  is measured by “pseudo-absolute”. Since the let out amount of the wire  12  can be measured more finely by means of the encoder  22 , combination of it with the linear sensor  38  allows more precise measurement of the let out amount to be made without changing the measurable let out amount of the wire  12 . 
     When the encoder  22  is used, light is picked up by a pick-up device  52  to thereby measure the angle of rotation of the encoder  22 . By detecting the angle of rotation of the encoder  22  by passing the wire  12  around the encoder  22 , the let out amount of the wire  12  can be measured. 
     Now, another embodiment of the present invention will be described. 
     When a wire is passed around the encoder directly, it is considered that the wire sometimes slips. 
     For example, when severe letting out or delivery of the wire is repeated, or when water, mud, and the like attaching to the wire are not completely cleaned off, the wire slips at the portion where it is passed around so that the movement of the wire becomes unable to be accurately represented by the encoder. 
     Then, by converting the shifted amount of the “pulley supporting member” supporting the movable pulleys into a rotating operation of the encoder by means of a non-slip timing belt, it becomes possible to accurately measure the delivered amount not affected by severe delivery or dirt on the wire. 
     The timing belt here is such a belt that is made of a resin with recesses and protrusions regularly formed thereon. By using the timing belt together with a timing belt pulley formed so as to engage the recesses and protrusions on the belt, the slip between the belt and the pulley can be prevented. 
     Referring now to FIG.  7  and FIG. 8, another embodiment will be described. 
     FIG. 7 is a schematic diagram showing a mechanism for transmitting the let out amount of the wire to the encoder, as another embodiment of the present invention. FIG. 8 is a diagram partly showing an enlarged timing belt. 
     The mechanism for transmitting the let out amount of the wire  12  to the encoder  122  is formed of timing belt pulleys  80 ,  82 , a timing belt  78 , and pulley supporting member  144 . To the pulley supporting member  144  are attached movable pulleys  30 ,  32 ,  34 , and  36 . By letting out or letting in the wire  12  thereby moving the movable pulleys  30 ,  32 ,  34 , and  36 , the pulley supporting member  144  is moved in the directions of the arrowheads X. 
     The timing belt pulley  80  is attached to the encoder  122 . The timing belt pulley  82  is rotatably attached to the displacement measuring apparatus. 
     As shown in FIG. 7, the timing belt  78  is passed around the timing belt pulleys  80 ,  82 . The timing belt  78  is provided with regular recesses and protrusions as shown in FIG.  8 . The timing belt pulleys  80  and  82  are formed so as to engage the timing belt  78 . The pulley supporting member  144  is provided with a belt fixing portion  145 . The belt fixing portion  145  is fixed to a portion of the timing belt  78 . 
     Since the mechanism for letting out or letting in the wire is configured as described above, when the pulley supporting member  144  is moved in the directions X, the shifted amount is converted into the rotated amount of the encoder by means of the timing belt  78  and the timing pulley  80 . 
     Since, here, the timing belt  78  and the timing belt pulleys  80  and  82  are arranged to engage with each other, no slippage occurs. 
     Therefore, accurate let out amount or let in amount of the wire  12  can be measured not affected by severe letting out or letting in of the wire or dirt on the wire. 
     The displacement measuring apparatus of the present invention can be applied to various types of displacement measurement. For example, the displacement measuring apparatus according to the invention can be used as a displacement measuring apparatus of the stroke of a hydraulic cylinder of heavy machinery. 
     FIG. 6 is a diagram showing an example of an shovel-car (heavy machine) provided with the displacement measuring apparatus of the invention. 
     A ground reveling tool (bucket)  58  of such a machine as an excavator (shovel-car)  56  is supported by a stick  60  and a boom  62  for rotation in specific directions and operated by cylinders  64 ,  66 , and  68  each of which is extended and retracted by hydraulic pressure. 
     In order to make ground reveling according to a predetermined grounding plan, it is required to control the position and attitude of the bucket  58 , and to achieve this, it becomes necessary to detect relative angles between the bucket  58  and the stick  60  supporting the same, the stick  60  and the boom  62  supporting the same, and the boom  62  and the construction machine  56  supporting the same. 
     The angle at a joint portion can be obtained by measuring the lengths of the three sides of the triangle including the fulcrum at each joint. 
     Therefore, in order to control the position and attitude of the bucket, it is required to measure displacement of the hydraulic cylinders. 
     Referring now to FIG. 6, an embodiment of a shovel-car with a displacement measuring apparatus of the invention attached thereto will be described. 
     The shovel-car  56  is made up of the shovel-car body  70 , boom  62 , stick (arm)  60 , and the bucket  58 . The hydraulic cylinder  64  is disposed between the shovel-car body  70  and the boom  62 . The hydraulic cylinder  66  is disposed between the boom  62  and the stick  60 . The hydraulic cylinder  68  is disposed between the stick  60  and the bucket  58 . The hydraulic cylinder  64  extends and retracts the cylinder rod so as to move the boom  62 . The hydraulic cylinder  66  extends and retracts the cylinder rod so as to move the stick  60 . The hydraulic cylinder  68  extends and retracts the cylinder rod so as to move the bucket  58 . 
     To the shovel-car body  70  is attached a level sensor  72 . On the ground surface  76  near the shovel-car  56 , there is disposed a rotating laser  74 . A laser beam from the rotating laser  74  is sensed by a level sensor  72 . The level sensor  72  sensing the laser beam from the rotating laser  74  is capable of level setting or gradient setting. 
     In the shovel-car  56  configured as described above, the displacement measuring apparatus of the invention can be installed on each of the hydraulic cylinders  64 ,  66 , and  68 . Namely, each of them can use the displacement measuring apparatus as a boom sensor, a stick sensor (arm sensor), and a bucket sensor. 
     The displacement measuring apparatus of the invention can be made into a smaller and narrower form, and hence it is easy to install and interference of the apparatus with other portion of the shovel-car  56  can be avoided. Therefore, the stroke amount (i.e., displacement) of each of the hydraulic cylinders  64 ,  66 , and  68  can be easily measured by the displacement measuring apparatus of the invention. As described above, the relative angle between the shovel-car body  70  and the boom  62 , the relative angle between the boom  62  and the stick  60 , and the relative angle between the stick  60  and the bucket  58  can be detected from the stroke amount of each hydraulic cylinder (i.e., displacement). 
     Accordingly, by using the levelness or gradient detected by the level sensor  72  and information of relative angles, it becomes possible to detect and control the position of the bucket  58 . 
     The present invention is not limited to the above described embodiments. 
     Although a wire is used as a general item in the above described embodiments, a special item other than that may be used. 
     Further, the linear sensor is not limited to the one of the above described type. An optical line sensor (CCD, LED) may also be used. It is also possible to measure the linear displacement by having a pressure sensor attached to the spring portion. 
     Further, the present invention is not limited to the mode in which the displacement measuring apparatus is used as the cylinder stroke measuring apparatus. It can be applied to measurement of other displacement. Of course, the invention is not limited to measurement of stroke amount of hydraulic cylinders. 
     Effects of the invention will be as follows: 
     According to the displacement measuring apparatus of the present invention, the apparatus can be formed smaller. It is also possible to provide the apparatus in a slender form. The apparatus in a slender form facilitates its installation on, for example, a heavy machine, and avoids its interference with other part. Because of ease of installation, the days required for installation can be decreased. 
     In the displacement measuring apparatus of the present invention, the displacement of each pulley is small as compared with the let out amount of the wire. In other words, only light load is placed on the energizing portion for energizing the pulleys, and, hence, endurance of the energizing portion is improved. Therefore, accuracy of the displacement measuring apparatus can be prevented from deteriorating. 
     Further, since a prior art encoder employing a spring is not used in the displacement measuring apparatus of the invention, deterioration of the measurement accuracy due to deterioration in the elasticity of the spring can be avoided.