Abstract:
A position control apparatus includes a stepping motor, a lead screw arranged to be rotated by the stepping motor being driven, a moving member arranged to move according to rotation of the lead screw, a first detecting device which detects that the moving member passes a particular position, a second detecting device which detects that the lead screw passes a particular rotating position, and a determination device which determines an amount of deviation of the moving member from a reference position on the basis of outputs from the first detecting device and the second detecting device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an improvement on a position control apparatus, a focus adjustment apparatus and a camera, for controlling the position of a moving member. 
     2. Description of Related Art 
     As methods for controlling the position of a lens barrel, there is known, as disclosed in Japanese Laid-Open Patent Application No. HEI 8-122617, a mechanism arranged such that a reference position of a lens barrel in the optical axis direction is decided by a discrimination means which is arranged to decide one reference position and, after that, an extent to which the lens barrel is to be drawn out is controlled by reading, with a photo-interrupter, the rotating position of a pulse plate (disk) provided on the shaft of a motor. 
     Some of cameras having zoom lenses are arranged to vary a photo-taking magnification by varying the positions of at least two lens groups in the optical axis direction. It is known that, in a camera of this kind, a drive source such as a stepping motor is arranged integrally with a first lens group to be capable of driving and moving a second lens group in the optical axis direction, the position of the second lens group in the optical axis direction is computed and obtained from information on the focal length of the photo-taking lens and information on a distance to an object to be photographed, and the second lens group is controlled and driven by the drive source to the computed position. A photo-taking lens barrel arranged in this manner obviates the necessity of a conventional mechanism called a mechanical cam mechanism which is arranged to control lens positions in the optical axis direction by means of cam grooves formed in a cam tube and rectilinear motion guide grooves formed in a rectilinear motion guide tube. 
     Generally, the structural arrangement described above is called an electronic zoom mechanism. In brief, the electronic zoom mechanism is arranged as follows. 
     Information on the focal length varied by a magnification varying action on the photo-taking lens is detected by a known position detecting means. A distance to the object to be photographed is detected by a known distance detecting means. The position of the second lens group relative to the first lens group necessary for focusing on the object is decided by these processes. The first lens group is provided with a detector for detecting the position of a part which is arranged at the second lens group to be detected by the detector. When a shutter release operation is performed by the camera user, the second lens group is driven to the position decided in relation to the first lens group on the basis of a detection signal of the detector. 
     BRIEF SUMMARY OF THE INVENTION 
     According to one aspect of the invention, there is provided a position control apparatus having a stepping motor, a lead screw arranged to be rotated by the stepping motor being driven and a moving member arranged to move according to rotation of the lead screw, the position control apparatus comprising a first detecting device which detects that the moving member passes a particular position, a second detecting device which detects that the lead screw passes a particular rotating position, and a determination device which determines an amount of deviation of the moving member from a reference position on the basis of outputs from the first detecting device and the second detecting device, so that it is possible to detect a larger amount of deviation than the above-stated arrangement of the prior art. 
     The above and further aspects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is a sectional view showing essential parts of a camera according to a first embodiment of the invention. 
     FIGS.  2 ( a ) and  2 ( b ) are diagrams for explaining the operation of a stepping motor which is composed of a two-phase coil part and a ten-pole magnet, according to the first embodiment of the invention. 
     FIG. 3 is a diagram for explaining a pattern of energizing the stepping motor by one-two-phase driving in the first embodiment of the invention. 
     FIG. 4 is a front view showing a second photo-interrupter and a pulse plate in a state obtained the instant a position detecting member has passed a first photo-interrupter in the first embodiment of the invention. 
     FIG. 5 is a block diagram showing the electrical arrangement of main parts of the camera in the first embodiment of the invention. 
     FIG. 6 is a flow chart showing an operation of the camera performed in detecting the position of a focusing lens group and deciding an amount of correcting a focusing lens moving action in the first embodiment of the invention. 
     FIG. 7 is a sectional view showing the arrangement of essential parts of a camera according to a second embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings. 
     FIG. 1 shows, in a sectional view, essential parts of a camera according to a first embodiment of the invention. Referring to FIG. 1, a shutter base plate  101  carries a shutter mechanism which includes shutter blades  105  and  106 . A rear base plate  102  is secured to the shutter base plate  101 . To the rear base plate  102  is secured a first lens group  123  which is held by a lens holding member  124 . A cam pin  103  is secured to the outer surface of the rear base plate  102 . 
     The cam pin  103  is arranged to be driven by the action of a cam tube and a rectilinear motion guide tube to move to a predetermined position. With the cam pin  103  driven, an optical unit  104  which is composed of the shutter base plate  101  and the rear base plate  102  is driven and controlled in the optical axis direction. 
     A focusing lens group  107  is held by a focusing lens group holder  108 . The focusing lens group holder  108  is arranged to be movable in the optical axis direction in a state of being carried by a support means which is fixedly disposed between the shutter base plate  101  and the rear base plate  102 . Reference numeral  109  denotes a lead screw. To one end part of the lead screw  109  on the side of the rear base plate  102  is secured a permanent magnet  110  which is a rotor of a stepping motor. 
     Two driving coils  111  and  112  are provided on the outer circumferential side of the permanent magnet  110 . The driving coils  111  and  112 , a pair of stator yokes  113  and  114  and another pair of stator yokes  115  and  116  are arranged to form a magnetic circuit for the stepping motor. A bearing metal part  117  is secured, by press fitting or the like, to the rear base plate  102 . The lead screw  109  is thus arranged to be rotatably carried by the bearing metal part  117  at its end part  109   a  on the side of the rear base plate  102 . A male thread is formed at the screw part  109   b  of the lead screw  109  to be in mesh with a nut member  118 . 
     The nut member  118  is carried by a nut holding part  108   a  formed at the focusing lens group holder  108 . When the lead screw  109  is caused to rotate by the stepping motor, the rotation of the lead screw  109  causes the focusing lens group holder  108  to move in the optical axis direction in the state of holding the focusing lens group  107 . At this time, since the focusing lens group holder  108  is biasedly urged in the direction of an arrow A by a spring or the like, the focusing lens group  107  can be moved without any deviation that otherwise might be caused to take place in the optical axis direction by a play or clearance  118   a  existing between the nut member  118  and the nut holding part  108   a.    
     A position detecting member  119  which is provided for position detection is secured to the focusing lens group holder  108 . To detect passing of the position detecting member  119 , a first photo-interrupter  120  (hereinafter referred to as the first PI  120 ) is secured to the shutter base plate  101  on the moving locus of the position detecting member  119 . The position of the focusing lens group  107  in the optical axis direction is detected jointly by the position detecting member  119  and the first PI  120 . The focusing lens group  107  is then driven by the stepping motor to a target position. 
     In the above-described arrangement, if the position of the first PI  120  is caused to vary by a change of temperature, for example, the amount of deviation of the position of the first PI  120  can be detected and corrected if the deviation is within a range of deviation, as will described below. 
     FIGS.  2 ( a ) and  2 ( b ) are diagrams for explaining actions of the stepping motor composed of two-phase coils and a ten-pole magnet. 
     FIG.  2 ( a ) shows the action of a mode of operation called the two-phase driving (full-step driving). In the two-phase driving, a current is constantly applied to the two coils and the rotor magnet is driven to rotate by changing the energizing phase from one phase over to another. The feed angle of the two-phase driving is 18 degrees per step. As shown in FIG.  2 ( a ), an energizing process to the coils is repeated in a cycle in the sequence of positions (1)→(2)→(3)→(4) in that order. According to the energizing process, the rotor magnet rotates counterclockwise by sequential steps (in the direction of an arrow shown in FIG. 28 a )). When the energizing sequence is reversed, the magnet rotor rotates clockwise in the manner reverse to the above process. 
     FIG.  2 ( b ) shows the action of another mode of operation called the one-two-phase driving (half-step driving). In the one-two-phase driving, the rotor magnet is driven at a feed angle which is one half of the feed angle of the two-phase driving. In other words, the feed angle of the one-two-phase driving is 9 degrees. As shown in FIG.  2 ( b ), an energizing process is performed in such a manner that energizing positions (1)′, (2)′, (3)′ and (4)′ ((3)′ and (4)′ being not shown) in which one of the two coils is not energized are inserted between the energizing positions (1), (2), (3) and (4) of the two-phase driving. 
     Although it is not shown in FIG.  2 ( b ), the energizing position (3)′ is obtained by not energizing the coil on the left side of the energizing position (3) shown in FIG.  2 ( a ). Also, the energizing position (4)′ is obtained by not energizing the coil on the right side of the energizing position (4) shown in FIG.  2 ( a ). 
     In the case of the one-two-phase driving as shown in FIG.  2 ( b ), the coils are energized in a cycle to obtain the above-stated positions in the sequence of (1)→(1)′→(2)→(2)′→(3)→(3)′→(4)→(4)′ in that order. According to the energizing process, the magnet rotor rotates counterclockwise as viewed in FIG.  2 ( b ). If the energizing sequence is reversed, the magnet rotor comes to rotate clockwise. 
     Now, it is assumed that the permanent magnet  110  of the stepping motor for driving the focusing lens group holder  108  in the optical axis direction is composed of the magnet rotor which is magnetized to have 10 poles, and that the coils  111  and  112  are energized in the above-stated pattern of the one-two-phase driving. In this instance, one turn of the magnet rotor is composed of 40 steps since the feed angle thereof per step is 9 degrees. 
     The focusing lens groups of compact cameras of zoom type of these days are trending to have a higher focus sensitivity under the influence of efforts being made in general to reduce the sizes of cameras and yet to increase their rates of magnification. Therefore, for feed control in moving a focusing lens group with a stepping motor or the like, it has become necessary to more finely arrange the amount of feed per step. If the amount of feed per step as required is 5 μm, for example, the screw pitch of the male screw  109   b  of the lead screw  109  and the nut member  118  becomes “5 μm×40 steps=0.2 mm”. 
     In the arrangement described above, in a case where a point of time when the position detecting member  119  comes to pass the first PI  120  varies under variable ambient temperature, the amount of feed is corrected in a manner as described below. 
     FIG. 3 shows the energizing pattern of the one-two-phase driving mentioned above. 
     Now, it is assumed that the position detecting member  119  is arranged to pass the first PI  120  at an energizing phase “a” as shown in FIG.  3 . When the position of the first PI  120  is caused to vary by the thermal expansion or contraction of the shutter base plate  101  under variable ambient temperature, for example, the phase of energizing pattern to be obtained when the position detecting member  119  pass the first PI  120  changes and deviates from a correct phase. If this change, or deviation, is within a range defined by the energizing phases (3) indicated by reference symbols “c” and “b” in FIG. 3, that deviation can be corrected. Since the amount of feed per step is 5 μm as mentioned above, the feed control can be accomplished by correcting the deviation within a range of ±3 steps before and after the energizing phase “a”, i.e., ±15 μm. The reason for this is that the direction in which the deviation takes place can be found from a difference between energizing phase patterns such as (1)→(1)′→(2)→(2)′ or (1)→(4)′→(4)→(3)′, as shown in FIG.  3 . 
     However, if the change or deviation is ±4 steps, i.e., ±20 μm, for example, energizing phases obtained at the ends of this range are both at the phase (3). In this case, therefore, the energizing phases “b” and “c” shown in FIG. 3 cannot be discriminated from each other. In the event of a further deviation of ±5 steps or more, there is a possibility that the correcting action is performed in a direction reverse to a correct direction. For example, if a change of temperature, in this case, causes the position detecting member  119  to pass the first PI  120  at a point (3)′ which is an energizing phase “d” in actuality as shown in FIG. 3, the correction system might mistake it for another point (3)′ which represents an energizing phase “e”. In the event of such a mistake, correction by −5 steps (which should be made in the right direction as viewed in FIG. 3) is erroneously replaced with correction by +3 steps (which should be made in the left direction as viewed in FIG.  3 ). This mistake then results in an error of the amount of feed by +8 steps. 
     In other words, for such a correction system, the positional deviations due to changes of temperature or the like must be suppressed not to exceed ±15 μm. However, it has been ascertained through tests that, in actual use of the camera, a change of room temperature from 20° C. to minus 10° C. causes the position of the first PI  120  to change or deviate by more than 10 μm. This value of deviation is computed on the basis of the linear expansion coefficient α of a polycarbonate resin material used for the camera. This coefficient is computed as follows: 
     
       
         α=2.8˜5.6×10 −5  cm/cm·° C. 
       
     
     It was found that a positional deviation of about 8 to 17 μm per cm takes place due to the changes of temperature. 
     Therefore, since the position of the first PI  120  changes to an extent exceeding the allowable limit of 15 μm at the temperature of environment under which the camera is expected to be used, it is hardly possible to substantially correct the amount of moving (feeding) the focusing lens group  107 . 
     In view of the above-mentioned point, the first embodiment is arranged to carry out the feed control by using a second detector in addition to the first detector described above. The second detector is described as follows. 
     Referring to FIG. 1, one end part  109   c  of the lead screw  109  is rotatably carried by a fitting engagement hole  101   a  of the shutter base plate  101 . A pulse plate  121  which rotates integrally with the lead screw  109  is secured to the fore end part of the lead screw  109  by press fitting or the like. The rotation of the pulse plate  121  is arranged to be detected by a second photo-interrupter  122  (hereinafter referred to as the second PI  122 ). 
     FIG. 4 is a plan view taken in the direction of an arrow B in FIG. 1 to show the second PI  122  and the pulse plate  121  in a state obtained the instant the position detecting member  119  passes the first PI  120 . 
     The pulse plate  121  is provided with a cutout  121   a  which is set to, in this instance, come to a symmetric position differing 180 degrees as viewed from the second PI  122 . It is assumed that the coil energizing phase of the stepping motor is (1), for example, when the cutout  121   a  comes to the symmetric position. Since the pulse plate  121  rotates integrally with the lead screw  109 , the rotation angle per step of the stepping motor obtained by the one-two-phase driving is 9 degrees. In FIG. 4, for the convenience of explanation, a pattern of energizing phases is shown in the sector areas of the pulse plate  121  obtained by dividing the pulse plate  121  at every 9 degrees. More specifically, in FIG. 4, a pattern of energizing phases to be detected by the detecting part  122   a  of the second PI  122  is shown on the pulse plate  121  assuming that the energizing phase obtained the instant the passing of the position detecting member  119  is detected by the first PI  120  is (1). After that, with the energizing process allowed to advance in the sequence of energizing phases (1)′, (2), (2)′, (3), (3)′, - - - , the pulse plate  121  rotates to bring the energizing phases shown on the pulse plate  121  to the detecting part  122   a  of the second PI  122 . In short, the pulse plate  121  serially rotates counterclockwise step by step. Then, at the twentieth step after detection of the energizing phase (1), the cutout  121   a  of the pulse plate  121  being rotated reaches the position corresponding to the detecting part  122   a  of the second PI  122 , so that the position of the cutout  121   a  of the pulse plate  121  is detected by the cutout  121   a  of the pulse plate  121 . 
     In FIG. 4, the range within which the positional deviations due to changes of temperature of the position detecting member  119  and the first PI  120  are correctable is represented by a hatched part  121   b . This correctable range  121   b  includes ±3 steps. As described in the foregoing, the amount of feeding (moving) the focusing lens group  107  becomes uncorrectable when the extent of deviation exceeds this correctable range  121   b . However, the above-stated correctable range can be widened by the use of the pulse plate  121  and the second PI  122 . 
     For example, it is assumed that the passing of the position detecting member  119  is detected by the first PI  120  at a position (4) which deviates by 6 steps in the energizing (phase) pattern, as indicated by reference numeral  121   c  in FIG. 4, due to a change of temperature or the like, while the passing of the position detecting member  119  should be detected by the first PI  120  at the phase position (1) in the energizing pattern. In this case, the deviation cannot be corrected by the above-stated arrangement of the position detecting member  119  and the first PI  120  alone. 
     However, the arrangement of the first embodiment having the pulse plate  121  and the second PI  122  is capable of correcting the deviation as described below. 
     After the passing of the position detecting member  119  is detected by the first PI  120  at phase (4) of the energizing pattern indicated by reference numeral  121   c  in FIG. 4, when the stepping motor is caused to rotate further counterclockwise as mentioned above, the cutout  121   a  of the pulse plate  121  is detected by the second PI  122  after 14 steps. 
     At this moment, it is possible to find that the detection is made when feeding is made only by 14 1steps while the detection should be made after feeding by 20 steps. In other words, the detection made after an amount of feed which is less by 6 steps than the correct number of feeding steps can be detected on the side of the camera body. Therefore, the feed control over the focusing lens group  107  can be accurately accomplished by correcting the amount of feed by 6 steps corresponding to the amount of deviation. The maximum number of steps correctable in this manner is ±19 steps. Any amount of positional deviation within this range is correctable. 
     The above-stated 19 steps correspond to an amount of feed of ±95 μm of the lead screw  109  in moving the focusing lens group  107 . Compared with the correctable range of ±15 μm of the system composed of only the position detecting member  119  and the first PI  120  mentioned in the foregoing, this correctable range is much wider and is sufficient for practical applications. 
     As regards the expansion and contraction of the lead screw  109  under variable ambient temperature, feed control can be more accurately carried out by presetting various correction amounts for various temperatures, by detecting outside air temperature with a temperature sensor and by making correction at the correction amount applicable to the temperature detected. 
     In a case where abrasion takes place at contact parts of the metal bearing part  117  and the end part  109   a  of the lead screw  109  shown in FIG. 1, the whole lead screw  109  shifts to the right, as viewed in FIG. 1, to an extent which corresponds to an amount of shavings caused by the abrasion. This results from the bias urging force of known urging means such as a spring on the focusing lens group holder  108 , because the lead screw  109  is also biasedly urged through the nut member  118  to the right as viewed in FIG.  1 . In that event, although there is no change in the positions of the position detecting member  119  and the first PI  120 , the pattern of energizing the stepping motor comes to change. The change in the energizing pattern tends to be mistaken for a change in position of the first PI  120 . 
     With the energizing pattern caused to change by the above-stated abrasion, correction of deviation would result in wrong feed control. Therefore, if the energizing pattern is found to have changed at a normal temperature by using a temperature sensor provided on the camera, the change of the energizing pattern is judged to have resulted from the abrasion and no correction is made. By virtue of this arrangement, a system can be prepared to perform no erroneous control in this respect. 
     It is also possible to carry out beforehand, at the time of assembling the camera, some process like a so-called break-in process to bring about abrasion at the above-stated contact parts to such a degree that the abrasion would not advance any further. That arrangement also gives a system which is free from the adverse effect of the abrasion of the contact parts mentioned above. 
     FIG. 5 is a block diagram showing the circuit arrangement of essential parts of the camera having the structural arrangement described above. All members that have already been described in the foregoing are indicated with the same reference numerals, and the details of them are omitted from the following description. 
     Referring to FIG. 5, a microcomputer  601  is arranged to control various actions of the camera. A first detecting circuit  602  is arranged to drive the first PI  120  and to send the output thereof to the microcomputer  601 . A second detecting circuit  603  is arranged to drive the second PI  122  and also to send the output thereof to the microcomputer  601 . An EEPROM 604 is a storage circuit. A stepping motor driving circuit  605  is arranged to drive the stepping motor. 
     FIG. 6 is a flow chart showing the operation of the first embodiment performed in detecting the position of the focusing lens group  107  and deciding an amount of correcting the amount of feeding (moving) the focusing lens group  107 . The flow of the operation is described with reference to FIG. 6 as follows. 
     At a step S 701 , the microcomputer  601  starts to execute a subroutine of detecting the position of the focusing lens group  107  and deciding an amount of correcting the position of the focusing lens group  107 . At a step S 702 , the stepping motor driving circuit  605  is caused to drive the stepping motor to feed the focusing lens group  107  by one step. At the next step S 703 , a check is made for a change in the signal from the first PI  120  through the first detecting circuit  602 . In other words, a check is made to find if the output of the first PI  120  has changed from a bright state to a dark state. If not, the flow of operation returns to the step S 702  to cause the stepping motor to continue its feeding action. After that, when a signal from the first detecting circuit  602  comes to indicate a change of the output of the first PI  120  from a bright state to a dark state at the step S 703 , that is, when the position detecting member  119  has reached the position of the first PI  120  (thus showing arrival of the focusing lens group  107  at the reference position), the flow proceeds from the step S 703  to a step S 704 . At the step S 704 , a counter N which is disposed within the microcomputer  601  is reset. At the next step S 705 , the count value of the counter N is incremented (advanced) by one. 
     At the next step S 706 , the stepping motor is driven forward by one step. At a step S 707 , the microcomputer  601  this time makes a check for a change of the output signal of the second PI  122  through the second detecting circuit  603 . If the output signal of the second PI  122  is found to have changed (from a dark state to a bright state). If not, the flow returns to the step S 705  to increment the count value of the counter N by one, allowing the stepping motor to carry on its feeding action at the step S 706 . When the output signal of the second PI  122  is found at the step S 707  to have changed to indicate arrival at the cutout part  121   a , the flow immediately proceeds from the step S 707  to a step S 708 . 
     While the camera is in the stage of manufacture, a value obtained during a period from detection of a change in the output signal of the first PI  120  until detection of a change in the output signal of the second PI  122  is stored in the EEPROM 604 (a design target value is “20”). At the step S 708 , a difference between the design target value and the count value of the counter N, i.e., “20−N” is considered to be the number of correction steps. The number of correction steps is used for control over the amount of feeding the focusing lens group  107 . Then, the flow of operation then quits this subroutine. 
     The arrangement of the first embodiment of the invention described above permits accurate correction of errors in amount of feeding the focusing lens group, which are caused by variable environmental conditions or changes due to ageing and has been hardly correctable by the conventional arrangement. 
     FIG. 7 is a sectional view showing the arrangement of essential parts of a camera according to a second embodiment of the invention. The parts shown in FIG. 7 correspond to the pulse plate  121  and the second PI  122  in the first embodiment described above. 
     Referring to FIG. 7, the fore end of a lead screw  501  is rotatably carried by a fitting engagement hole  502   a  provided in a shutter base plate  502 . The fore end part of the lead screw  501  which pierces through the shutter base plate  502  has a magnetic  503  secured thereto as one unified body therewith. A magnetic sensor  504  is arranged to detect the passage of the magnet  503  at the front part of the magnetic sensor  504 . 
     The magnet  503  and the magnetic sensor  504  are arranged in combination to be capable of carrying out the same function as the function performed by the pulse plate  121  and the second PI  122  in the first embodiment described in the foregoing. Further, in this case, a part of the lead screw  501  may be magnetized to have the same function as the function of the magnet  503 . 
     The arrangement of the second embodiment permits the detecting part described in the foregoing to be arranged in a different manner. Therefore, the arrangement of the second embodiment serves to enhance the practicability of the detecting part arranged in accordance with the invention. 
     The invention is not limited to the embodiments disclosed but is intended to cover various modifications and equivalent arrangements to be made within the scope of technology of the invention. For example, if the concept of the embodiments disclosed in the foregoing is changed to have the position detecting member  119  formed with a pressed plate and secured to the focusing lens group holder  108  by adhesion means or the like, the detected position tends to deviate when the adhesion means is caused to peel off by repeated changes of temperature or a shock inflicted thereon with the camera accidentally dropped or when the pressed plate deforms. 
     On the other hand, possible deviations of detection made by the pulse plate  121  result solely from the shavings of the metal bearing part resulting from abrasion and from the expansion and contraction of the lead screw  109  caused by changes of temperature as mentioned above. The deviation due to the shavings at the metal bearing part is arranged to be prevented by carrying out a break-in process to eliminate the possibility of further having the shavings as mentioned in the foregoing. As for deviations due to changes in temperature, the correction can be made by using amounts of expansion and contraction obtained from a linear expansion coefficient according to outside air temperature. 
     In the arrangement described above, the feed control over the focusing lens group may be changed as follows. The position of the pulse plate  121  detected by the second PI  122  after detection by the first PI  120  is set as a reference position and, after that, the feed control is performed by correcting only the amount of expansion and contraction of the lead screw  109  caused by the changes of temperature. 
     In the embodiments disclosed, the amount of deviation due to changes of temperature, etc., is corrected by counting the number of steps of the stepping motor and by comparing the count value thus obtained with a target value stored in the EEPROM. However, this arrangement of course can be changed to perform control on the basis of time, because a length of time required for driving by one step is beforehand known. 
     The reference position obtained by the first PI  120  may be set at a physical abutting position. 
     While the embodiments disclosed are arranged to use a stepping motor as a drive source for driving the focusing lens group, the stepping motor may be replaced with an ordinary DC motor or the like. 
     In the cases of the embodiments disclosed, the invention is applied to cameras. However, the invention is applicable also to other focus adjustment apparatuses and position control apparatus having moving members such as lenses or the like. 
     Further, the software arrangement and hardware arrangement of the embodiments described in the foregoing can be interchanged as desired.