Abstract:
A distance measuring sensor includes a case subassembly having inside a light emitting element and a light receiving element, and a lens case subassembly having a projection lens projecting a light output from the light emitting element and a condenser lens condensing the light reflected from the object, and attached to a front side of the case subassembly. The condenser lens is movably attached to the lens case subassembly, and after an output is adjusted, this condenser lens is fixed thereto. Thus, the distance measuring sensor enabling easier adjustment of an output can be provided.

Description:
This nonprovisional application claims priority under 35 U.S.C. §119(a) on patent application Ser. No. 2002-088606 filed in JAPAN on Mar. 27, 2002, which is herein incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a distance measuring sensor detecting a position and a tilt of an object, a distance to the object and the like, by projecting a light on the object and receiving the light reflected therefrom, and a method for manufacturing such a distance measuring sensor. 
   2. Description of the Background Art 
   As a device for measuring a distance to an object, a distance measuring sensor applying a so-called triangle measuring method is known.  FIG. 11  is a schematic view of the distance measuring sensor applying a so-called triangle measuring method, which should be referred in a following description of the principle of distance measurement thereof. A pulsed light output from a light emitting element, i.e., a light emitting diode (LED)  101 , becomes a narrow beam through a projection lens  133 , and projected on an object  150  or  160 . The light reflected from object  150  or  160  is condensed on a light receiving face of a light receiving element, i.e., a semiconductor position sensitive detector (PSD), by a condenser lens  138 . 
   Here, as shown in  FIG. 11 , a condensing position (spot position) where reflecting light is condensed by condenser lens  138  may vary in accordance with the distance from the distance measuring sensor to the object. By arranging the light receiving face of PSD  102  so as to cover the variation range of the condensing position, and processing a pair of photocurrent outputs from PSD  102 , the distance to the object can be measured. It should be noted that a divided type photodiode having a plurality of light receiving faces may be used as a light receiving device other than the PSD. 
     FIG. 12  is a cross-sectional view showing a structure of a conventional distance measuring sensor using above-mentioned triangle measuring method. In conventional distant measuring sensor  110 , LED  101 , PSD  102 , and a control IC  103  are mounted by die bonding, wire bonding or the like, on a lead frame  108 . A translucent resin  109  is molded over these elements. Further, a case  111   a  consisting of an opaque resin is molded over translucent resin  109 . Here, optical windows for passing lights are provided at least to the upper face of case  111   a  facing to LED  101  and PSD  102 . A lens case  111   b  in which projection lens  133  and condenser lens  138  are integrally molded with the translucent resin is attached on case  111   a.    
     FIG. 13  is a circuit diagram of the conventional distance measuring sensor. A clock pulse having a prescribed period from an oscillator circuit arranged in a signal processing circuit  106  is provided to a timing generator circuit similarly arranged in signal processing circuit  106 , and thus a drive pulse is generated. The drive pulse is input to light emitting circuit  104 , and then LED  101  emits light. 
   A pair of feeble photocurrent outputs obtained by PSD  102  sensing the reflecting light is amplified by an amplifier circuit  105  and input to signal processing circuit  106 . An operation processing based on this input signal is performed in signal processing circuit  106 , and the result thereof is output to the outside via an output circuit  107 . Normally, light emitting circuit  104 , amplifier circuit  105 , signal processing circuit  106 , and output circuit  107  are integrally packaged in one control IC  103 . 
   As for signal processing schemes, there are an analog output scheme in which an output value fluctuating in accordance with the distance, as shown in  FIG. 14 , is provided as information of a distance to an object, and an H/L output scheme in which an output value and a preset threshold value are compared and the result is output as a high (H) or a low (L) pulse. 
   On the other hand, in either output scheme, errors exist between the actual distance to an object and the output value of the distance measuring sensor. The errors may occur due to (1) variation in attaching position precision of LED, the projection lens, the condenser lens, and PSD, and (2) variation in element characteristics such as light emitting characteristics of LED, and light receiving characteristics of PSD. 
   For example, in the analog output scheme, such variations result in an output characteristics curve D or E shown by dotted lines in  FIG. 14  that varies relative to a reference output characteristics curve C shown by solid line. Thus, errors occur between the actual distance to an object and the output value of the distance measuring sensor due to the above-mentioned variation in attaching position precision and variation in element characteristics. It applies to the H/L output scheme as well. 
   As a method for reducing the errors in output, one possible method is to measure the distance, after completing assembly of a distance measuring sensor, to an actually installed object with the distance measuring sensor and adjusting the obtained output value to a correct value. 
   For example, as shown in  FIG. 13 , one of the possible method is to arrange an external variable resistor  107   a  connected to output circuit  107  beforehand, and adjust the resistance value R of external variable resistor  107   a  to electrically adjust the output value for reducing the errors. On the other hand, the external circuit is required separately when using this method, which increases the manufacturing costs. 
   Another possible method is to correct the output of the distance measuring sensor with a microcomputer and the like by a user, without any adjustment in the manufacturing process of the distance measuring sensor. This method, however, will be a burden to a user, and therefore not preferable. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is to provide a distance measuring sensor enabling easier adjustment of its output, and a method for manufacturing the same. 
   A distance measuring sensor according to the present invention includes a light emitting element; a projection lens projecting to an object a light output from the light emitting element; a condenser lens condensing the light reflected from the object; and a light receiving element arranged at a position to which the light is condensed by the condenser lens, and receiving the light at a light receiving face to transmit an output signal that varies in accordance with a position of the object. The condenser lens is attached to a support member having a guide mechanism that enables the condenser lens to move in a prescribed direction, and the condenser lens is immovably fixed to the guide mechanism. 
   Thus, by this mechanical scheme enabling the alignment of condenser lens by movably attaching the condenser lens to the support member, the output of the distance measuring sensor can be adjusted very easily. A scheme in which alight receiving element is aligned requires a highly complicated device arrangement and alignment tasks, from a viewpoint of electrical connections of the light receiving element. In the present configuration, however, by enabling movement of the condenser lens, not only adjustment of the output of the distance measuring sensor is easily achieved, but also manufacturing of the distance measuring sensor is enabled, in compact size and at low costs with a smaller number of parts than the light receiving element aligning scheme. Note that, after completing the alignment, the condenser lens needs to be immovably fixed to avoid displacement under the effect of vibration or the like. 
   Desirably, in the distance measuring sensor according to the present invention, a moving direction of the condenser lens includes at least a direction parallel to a straight line connecting the light emitting element and the light receiving element. The output of the distance measuring sensor can be adjusted if the condenser lens is movable at least in the above-mentioned direction. If the condenser lens is attached to a support member enabling the movement in one direction, then designing and manufacturing of the distance measuring sensor is easy and its implementation will be facilitated. 
   Desirably, in the distance measuring sensor according to the present invention, the condenser lens is aligned and fixed to the support member so as to obtain a correct output signal corresponding to a position of the object. Thus, by fixing the condenser lens in order to avoid displacement after completing alignment, which has been movably attached to the support member, the distance measuring sensor may be provided that outputs signals stably and accurately for a long period. 
   Desirably, in the distance measuring sensor according to the present invention, for example, the condenser lens is fixed to the support member by a light curing adhesive or an instant adhesive. By employing the light curing adhesive or the instant adhesive for fixing the condenser lens to the support member, displacement at the time of fixing them can be avoided. When a heat curing adhesive is used, for example, redundant external force is applied by the thermal expansion of the condenser lens or the support member, which results in the displacement of the condenser lens. In contrast thereto, no external force is generated if the light curing adhesive or the instant adhesive is used, thus the displacement of the condenser lens does not occur. 
   Desirably, in the distance measuring sensor according to the present invention, for example, an engaging channel extending in the moving direction is provided to one of the condenser lens and the support member, and an engaging rib engaging with the engaging channel is provided to the other one. Thus, by providing the guide mechanism consisting of the engaging channel and engaging rib to the condenser lens and the support member, the moving direction of the condenser lens can easily be determined. As a result, the output of the distance measuring sensor can easily adjusted. 
   Desirably, the distance measuring sensor according to the present invention further includes, for example, an output adjusting terminal outputting an output signal from the light receiving element to the outside when the condenser lens is at any one position in the moving direction. Thus, by providing the output adjusting terminal enabling monitoring of the output of the light receiving element at its position when aligning the condenser lens, the adjustment of the output can be performed easily. The output adjusting terminal is desirably distinguished from an original output terminal of the distance measuring sensor and configured to output a signal, which is a simply amplified photocurrent signal. 
   Desirably, the distance measuring sensor according to the present invention further includes, for example, a first subassembly structured by the light emitting element and the light receiving element mounted on a same substrate attached to a case; and a second subassembly attached to a front side of the first subassembly and including the projection lens, the condenser lens and the support member. Thus, by configuring the assembly by separate subassemblies, the first subassembly to which the elements are attached can rather be used generally. Specifically, according to the present configuration, only the second subassembly should be modified in accordance with a specification while the first subassembly is commonly used, thus the distance measuring sensor addressing various specifications can be provided at low costs. 
   Desirably, in the distance measuring sensor according to the present invention, for example, a shield plate consisting of a conductive material is interposed between the first subassembly and the second subassembly; and the distance measuring sensor may be attached to an electronic device at any angle by changing a protruding direction of a shield terminal of the shield plate relative to the case. Thus, by changing a protruding direction of the terminal of the shield plate interposed between the first subassembly and the second subassembly to various direction, the light projecting direction relative to the substrate of the electronic device to which the distance measuring sensor is attached may be set freely. 
   A method for manufacturing a distance measuring sensor according to the present invention, in which the distance measuring sensor includes a light emitting element; a projection lens projecting to an object a light output from the light emitting element; a condenser lens movably attached to a support member and condensing the light reflected from the object; and a light receiving element arranged at a position to which the light is condensed by the condenser lens, and receiving the light at a light receiving face to transmit an output signal that varies in accordance with a position of the object; includes a step of aligning and fixing the condenser lens so as to obtain a correct output signal corresponding to a position of the object. 
   Thus, by including the step of aligning the condenser lens movably attached, the output adjustment can be achieved in a very simple manner. 
   Desirably, in the method for manufacturing the distance measuring sensor according to the present invention, for example, the alignment of the condenser lens is performed while monitoring an output signal for adjustment provided from the light receiving element. Thus, by monitoring the output signal for alignment concurrently with aligning the condenser lens, the alignment of the condenser lens can be achieved more easily. 
   Desirably, the method for manufacturing the distance measuring sensor according to the present invention further includes, for example, a step of fixing the condenser lens to the support member with a light curing adhesive or an instant adhesive. Thus, by fixing the condenser lens by the light curing adhesive or the instant adhesive, the displacement of the condenser lens may be prevented. 
   The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a case subassembly configuring a distance measuring sensor according to a first embodiment of the present invention; 
       FIG. 2  is a cross-sectional view of the case subassembly configuring the distance measuring sensor according to the first embodiment of the present invention, along a line II—II in  FIG. 1 ; 
       FIG. 3  is a perspective view of the distance measuring sensor according to the first embodiment of the present invention; 
       FIG. 4  is a cross-sectional view of the distance measuring sensor according to the first embodiment of the present invention, along a line IV—IV in  FIG. 3 ; 
       FIG. 5  is a cross-sectional view of the distance measuring sensor according to the first embodiment of the present invention, along a line V—V in  FIG. 3 ; 
       FIG. 6  is a schematic view of the distance measuring sensor of the present invention, related to a description of principle of alignment thereof; 
       FIG. 7  is a circuit diagram of a position detection circuit of the distance measuring sensor according to the first embodiment of the present invention; 
       FIG. 8  is a perspective view of a structure of a distance measuring sensor according to a second embodiment of the present invention; 
       FIG. 9  is a cross-sectional view of the structure of the distance measuring sensor according to the second embodiment of the present invention, along a line IX—IX in  FIG. 8 ; 
       FIG. 10  is a perspective view showing another application of the distance measuring sensor according to the second embodiment of the present invention; 
       FIG. 11  is a schematic view of the distance measuring sensor applying a so-called triangle measuring method, related to a description of principle of distance measurement thereof; 
       FIG. 12  is a cross-sectional view showing a structure of a conventional distance measuring sensor; 
       FIG. 13  is a circuit diagram of the conventional distance measuring sensor; 
       FIG. 14  shows variation in element characteristics of PSD; 
       FIG. 15  is a top view of a lead frame showing a structure of a distance measuring sensor studied by the inventor; and 
       FIG. 16  is a top view of a lead frame showing a structure of another distance measuring sensor studied by the inventor. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The inventor considered to implement a distance measuring sensor that enables mechanical adjustment of an output. First, referring to  FIGS. 15 and 16 , distance measuring sensors related to the present invention will be described. 
   In a distance measuring sensor shown in  FIG. 15 , an attaching position of PSD  202  to be attached on lead frame  208  is adjustably configured. Specifically, an electrode  260  on lead frame  208  to which a terminal of PSD  202  is connected is formed larger than electrodes to which terminals of LED  201  and control IC  203  are connected. Thus, it will be possible to adjust the attaching position of PSD  202  to lead frame  208  in the direction indicated by an arrow F, while monitoring the output of the distance measuring sensor. This alignment achieves the adjustment of the output. According to this scheme, however, the very difficult task is required, that the user must determine the attaching position of PSD  202  while monitoring the output of the distance measuring sensor, and thus it is not preferable. 
   In a distance measuring sensor shown in  FIG. 16 , a lead frame is divided into lead frames  308   a  and  308   b , and LED  301  and PSD  302  are mounted thereto, respectively. Specifically, the adjustment of the output is performed after the mounting, by aligning lead frame  308   b  in the direction indicated by an arrow G in the figure, while monitoring the output. According to this scheme, however, a flexible wiring  307  and the like for allocating to an electrical connection of divided lead frames  308   a ,  308   b , which increases the manufacturing costs. Additionally, it undesirably increases the size of the device. 
   The present inventor has finalized the present invention after studying for avoiding such problems associated with above-mentioned schemes. In the following, referring to the figures, embodiments of the present invention will be described. 
   First Embodiment 
   First, referring to  FIGS. 1 and 2 , a structure of a case subassembly  10  configuring a distance measuring sensor according to a first embodiment of the present invention will be described. Case subassembly  10  of a first subassembly includes therein a lead frame  8  to which an LED  1 , a PSD  2 , and a control IC  3  are mounted. A translucent resin  9  is molded over LED  1 , PSD  2  and control IC  3 . Further, a case  11  consisting of an opaque resin is molded over translucent resin  9 . Note that optical windows  12  and  13  for passing lights are provided at the upper portion of case  11  corresponding to LED  1  and PSD  2 , respectively. A terminal  8   a  used as an electrical lead to the outside protrudes from a prescribed position of case  11 . Terminal  8   a  extends from lead frame  8  to the outside of case  11 . Case  11  is also provided at its lateral face with a slit  14  to which a shield terminal  24  of a shield, which will be described later, is fitted (see FIG.  3 ). 
   Next, referring to  FIGS. 3  to  5 , the structure of the distance measuring sensor according to the present embodiment will be described. The distance measuring sensor of the present embodiment is configured by mounting a lens case subassembly  30  of a second subassembly to the above-mentioned case subassembly  10  of the first subassembly. Further, preferably a shield is interposed between case subassembly  10  and lens case subassembly  30 . Optical windows  22  and  23  for passing lights are provided at prescribed positions of a shield face  21  of the shield. 
   Here, lens case subassembly  30  has a cap forming portion  31 , which is a support member designed to cover the top face of the above-mentioned case subassembly  10 , and a protrusion  32 , to which projection lens  33  is attached. Further, at a prescribed position on the top face of cap forming portion  31 , a guiding frame  34  engaging with a movable member  36  equipped with a condenser lens  38  is provided. 
   At a prescribed position of guiding frame  34 , a guiding rail  35  of an engaging rib is formed. Guiding rail  35  extends in the same direction as the moving direction of condenser lens  38  (indicated by an arrow A in the figure). More specifically, it extends parallel to the light receiving face of PSD  2  and also parallel to a straight line connecting LED  1  and PSD  2 . To a prescribed position of movable member  36  equipped with condenser lens  38 , a guiding channel  37  of an engagement channel is formed, which engages with guiding rail  35  provided at above-mentioned guiding frame  34 . With such a configuration, by pushing movable member  36  equipped with condenser lens  38  against guiding frame  34  of cap forming portion  31 , condenser lens  38  can easily be attached movably to cap forming portion  31  of the support member. 
   With the configuration above, the distance measuring sensor to which condenser lens  38  is movably attached is implemented. In this distance measuring sensor, as shown in  FIG. 6 , since condenser lens  38  is movable in the direction indicated by an arrow A in the figure, the adjustment of its output can easily be performed. Specifically, by moving condenser lens  38 , the light that has been projected onto an object from LED  1  via projection lens  33  and reflected therefrom can be condensed at any position on the receiving face of PSD  2 . Therefore, by moving the condenser lens to a position where a correct output is obtained, the output can easily be adjusted. 
   In manufacturing the present distance measuring sensor, it is preferable to fix movable member  36  and cap forming portion  31  with a light curing adhesive or an instant adhesive, after the above-mentioned alignment of condenser lens  38 . This is to avoid the displacement of condenser lens  38  after the alignment. As a light curing adhesive, a UV adhesive or a visible light curing adhesive may be used, for example. By using a light curing adhesive or an instant adhesive, condenser lens  38  can be fixed to an appropriate position without displacement resulting from redundant external force. 
   Further, in this configuration, the distance measuring sensor is configured by separate case subassembly  10  and lens case subassembly  30 . By dividing the assembly into two parts, it becomes possible to utilize case subassembly  10  for general purpose. Specifically, when manufacturing distance measuring sensors with different specification in measuring range, case subassembly  10  can commonly be used, while only lens case subassembly may be modified addressing to the respective specifications, and thus the manufacturing costs can be reduced. 
   It should be noted that, as shown in  FIG. 7 , the circuit configuration of the distance measuring sensor according to the present embodiment is different in part from that of a conventional sensor. Specifically, an external variable resistor which is conventionally provided to output circuit  7  is eliminated. Additionally, between amplifier circuit  5  and signal processing circuit  6 , a terminal for the output adjustment which enables to extract an output for adjustment independently. Thus, by monitoring the output of the light receiving element from the output adjustment terminal during output adjustment of the distance measuring sensor, it will be possible to guide the condenser lens to an optimum position. When the output adjustment is performed using the conventional output terminal, time rug often occurs since the operation processing is performed in the signal processing circuit  6 . Therefore, it is preferable to provide a separate output adjustment terminal that is independent from signal processing circuit  6 , as in the present embodiment. 
   Second Embodiment 
   Next, a distance measuring sensor in a second embodiment will be described. To parts that are identical to that of the first embodiment will be given identical reference characters in the figures, and description thereof will not be repeated. 
   In a distance measuring sensor according to the present embodiment, case subassembly  10  similar to that of the first embodiment is used. The lens case subassembly, however, has a structure different from that of the first embodiment. As shown in  FIGS. 8 and 9 , on the top face of cap forming portion  41  of lens case subassembly  40 , a raised portion  42  equipped with a projection lens  43  is formed. This raised portion  42  includes a concave portion  44 , at its prescribed position, to which a movable member  46  equipped with a condenser lens  48  is mounted. At a side wall of concave portion  44 , a guiding channel  45  of an engagement channel extending in the same direction as the moving direction of condenser lens  48  (the direction indicated by an arrow B in the figure) is formed, and an engaging rib  47  engages with guiding channel  45 . By the configuration above, the distance measuring sensor to which condenser lens  48  is movably attached can be implemented. 
   The distance measuring sensor shown in  FIG. 8  is a so-called side view type distance measuring sensor in which a light is projected in the horizontal direction relative to a substrate of an electronic device to which the distance measuring sensor is attached, it can easily be modified to a so-called top view type distance measuring sensor, as shown in  FIG. 10 , in which a light is projected in the normal direction of a substrate of an electronic device to which the distance measuring sensor is attached, by modifying protruding direction of terminal  8   a  extending from lead frame  8  and that of shield terminal  24  extending from the shield. 
   In the embodiment above, the example has been described in which the distance measuring sensor is configured by separate case subassembly and lens case subassembly, but the present invention is not limited to this configuration. Other configuration may optionally employed, as long as it remains as a distance measuring sensor having the configuration in which the condenser lens is movably attached to the support member, and adjustment of an output can be achieved by aligning the condenser lens. 
   Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.