Abstract:
A method and apparatus for preventing excessive closure between a retractable tip objective and the stage of a microscope which includes positioning a sensor in the turret of a microscope, which sensor is capable of detecting excessive retracting of the retractable tip into the body of the objective, and providing a controller for monitoring the sensor for such excessive retracting and issuing an alert in response to the detection of an event of such excessive retracting. The alert may be made by way of an audio output, or by a visual cue or both. Extinguishing the lamp of the microscope is a preferred visual cue, as the excessive retracting of the retractable tip is generally caused by a focusing error, and the extinguishing of the light source reduces or eliminates the ability of the user of the microscope to focus the microscope, thus attracting his or her attention.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to the field of optical microscopes, and, in particular, to a method and apparatus for the prevention of application of excessive force between the objective or objective housing of a microscope and the stage thereof.  
         BACKGROUND OF THE INVENTION  
         [0002]    Modem optical microscopes are generally equipped with an eyepiece or eyepieces which are mounted to a microscope. Multiple objective lenses are mounted to the microscope-body and are carried by a turret which allows each lens in turn to be rotated into a light path extending through the microscope body from the objective to the lenses in the eyepieces. The sample to be studied is generally placed on a stage which is likewise mounted to the body of the microscope at a position beneath the objective. Illumination is frequently provided by means of a lamp mounted below the stage which is positioned to shine upward through an aperture in the stage. Biological microscopes typically require the sample to be mounted on a glass slide which is in turn placed on the stage where it may be held in place by clips. To focus the image, the distance between the objective and the stage is adjusted. This is generally accomplished by raising and lowering the stage, but is sometimes accomplished by raising and lowering the objective. For simplicity, the relative motion of the stage and objective will be discussed as raising and lowering of the stage, since raising and lowering of the objective produces essentially the same result.  
           [0003]    The raising and lowering of the stage is generally accomplished by means of one or more focusing knobs located on the side of the microscope body. The knobs may include a fine adjustment knob and a coarse adjustment knob. The turning of the fine adjustment knob through a given angle results in less motion of the stage than the turning of the coarse adjustment knob.  
           [0004]    When a sample is out of focus and the user is looking through the eyepiece or eyepieces of the microscope, the user does not see the fine detail of the sample. Rather, the user may only see a blurred and indistinct image. As the sample begins to come into focus, the blurring abates and the fine detail of the sample can be perceived. The transition from a blurred image to an in-focus image occurs over a rather short range of travel of the stage, particularly at high magnifications. As a result, finding the focus can be rather difficult, and it is not uncommon for a microscope user to turn the focus adjustment knobs in the wrong direction while seeking focus.  
           [0005]    If the user raises the stage too high during the focusing process, contact between the objective and the slide may result. If too much pressure is applied at this point, the slide can break, the sample can be spoiled and the objective can be contaminated. The slide breakage problem is particularly acute with higher magnification objectives. This problem of slide breakage is longstanding, and affects even experienced microscope users.  
           [0006]    Various means of reducing or eliminating the problem have been devised. One approach to avoiding the problem of slide breakage is the use of retractable objective carriers. According to this approach, the objective lenses of the microscope are mounted in carriers which are slidably mounted in the objective housings. Other lenses may be fixedly mounted in the objective housing. A spring acts between the objective housing and the carrier to bias the carrier to its fully downwardly-extended position. Flanges or stops on the objective housing and carrier retain the carrier within the objective housing.  
           [0007]    If a user of such a microscope raises the stage to the point where the carrier touches the slide, the carrier retracts into the objective housing. Generally, such carriers are capable of being retracted up to about ¼ inch (6.4 mm). At this point, the carrier reaches an internal stop which prevents it from retracting further into the objective housing. Such retractable objective carriers are seldom employed with lower power objectives, such as 2× through 10× objectives. Occasionally, they are found on 20× objectives, but, more commonly, they are used only on objectives of 40× or 100× or greater. The reason for this is that the higher power lenses typically have a much shorter working distances. For example, the working distance of a 100× objective is about 0.6 mm. Thus, even a minor amount of adjustment of the stage can result in breakage of the slide. As a result, the retractable objective carrier has not provided a complete solution to the slide breakage problem.  
           [0008]    Another approach that has been taken is the providing of mechanical stops that limit the upward travel of the stage. Such stops may work in cooperation with the fine and coarse adjustment mechanisms, and are generally adjustable. The stop is generally intended to be set to prevent the coarse adjustment mechanism from raising the stage above a user-selected point. Typically, manuals for microscopes having such stops suggest that the stops be set using the highest power objective, which is typically 100×. The sample is first placed in focus at this setting, and the stop is then set. Since most modern microscopes are parfocal (all lenses focus on a given sample at the same stage elevation), no lens should need to have the stage raised beyond this point. This provides the two benefits of reducing slide breakage and allowing the focusing the microscope a single time, and achieve focus with any lens by adjusting the coarse focus until the stop is reached. Stops are generally not associated with the fine focus.  
           [0009]    Unfortunately the use of stops has not eliminated slide breakage. First, few users know how to adjust the stops properly. In addition, many users who are familiar with the stop mechanism choose not to take the time to set it up and use it. Those users who do set the slide mechanism properly frequently do not check the adjustment on a daily basis. Finally, commercially-available slides vary in thickness, as do samples that are to be observed. As a result, frequent resetting of the stop would be necessary for each sample to ensure that slide breakage is avoided. Even if the stop is properly set, it should be noted that current stops only affect the coarse adjustment. Slide breakage frequently occurs as a result of use of the fine adjustment mechanism.  
           [0010]    Thus, there remains an unfulfilled need for a system that will prevent slide breakage during adjustment of the height of the stage.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention provides a method and apparatus for reducing slide breakage due to raising of the stage into contact with an objective. This is accomplished by the use of retractable objective carriers slidably mounted in the objective housings. A proximity sensor is positioned above the carrier, and is configured to detect the proximity of the carrier before the upper stop is reached. When the proximity sensor detects the proximity of the carrier (or an extension of the carrier), the system is activated to emit an audible signal and to extinguish the stage light that illuminates the sample. The extinguishing of the light serves as an indication that the stage has been raised too high. Further attempts to focus the microscope on the sample by further raising the stage are discouraged by the fact that the sample generally is not sufficiently visible for focusing once the light has been extinguished.  
           [0012]    Unlike systems which incorporate stops to prevent excessive raising of the stage, the present system has the advantage of not requiring any expertise on the part of the user. The sounding of the tone and the extinguishing of the light are generally sufficient to stop even an inexperienced microscope user with no knowledge of the system from continuing to turn the focus adjustment knobs. It also has the advantage of continuing to function properly despite changes in slide or sample thickness. The system can be assembled with a single proximity sensor mounted to the stationary portion of the turret, so that a separate proximity sensor is not needed for each objective, and so that no wiring needs to extend into the objective housing, with the added complexity, need for slip rings or other contacts, and cost that would otherwise be entailed.  
           [0013]    Many different types of proximity sensors may be used, including leaf springs, microswitches, break-beam sensors, magnetic and inductive proximity sensors, and pressure sensors. One inexpensive, adjustable, reliable sensor that has been found to function well for this application is the reflective object sensor, such as that sold by Optek Technology, Inc. of 1215 Crosby Road, Carrollton, Tex. 75006 under the model number OPB6808A. Such sensors may consist of an infrared emitting diode and an NPN silicon phototransistor mounted beside one another, with both devices being mounted on parallel axes. The devices are unfocused and are contained in a housing that is sufficiently transparent to the infrared light emitted by the infrared emitting diode, but which blocks a significant portion of the visible spectrum. The sensitivity of the device can be adjusted by an external resistance device such as a resistor or potentiometer, so the microscope according to the present invention may be calibrated to signal retraction of the retractable portion of an objective before it reaches the internal stop. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a side elevation of a microscope according to the present invention with one objective shown in cross-section.  
         [0015]    [0015]FIG. 2 is a cross-sectional view of a retractable tip objective of the prior art.  
         [0016]    [0016]FIG. 3 is a cross-sectional view of a retractable tip objective according to the present invention.  
         [0017]    [0017]FIG. 4 is a schematic diagram of a controller circuit for the device according to the present invention.  
         [0018]    [0018]FIG. 5 is a flow diagram of the operating program for the device according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    Referring first to FIG. 1, a typical microscope  10  has a frame  11 , a stage  12  slidably mounted to the frame, an illuminator system  13  for transmitting light from a bulb  14  through an aperture in the bottom of the stage  12 . The microscope is typically fitted with three or more objectives  15 - 17  which are mounted on a turret  18 . The objectives receive light from the bulb  14  and transmit it along a light path to the eyepiece  21 .  
         [0020]    The principal means of focusing the microscope is by use of the coarse adjustment  22  and fine adjustment  23 . The coarse adjustment  22  is turned to raise and lower the stage. The fine adjustment  23  moves the stage  12  a smaller amount per rotation than the coarse adjustment to facilitate precise focusing. Typically, a specimen is mounted on the microscope stage by placing it on a slide  24  and placing the slide on the stage  12 . The coarse and fine adjustment knobs  22 ,  23  are then used to adjust the position of the stage nearer to or farther away from the selected objective  15 - 17  in order to bring the specimen into focus.  
         [0021]    Conventional retractable tip objectives  25 , such as that shown in FIG. 2, have been known in the art for some time. Such objectives include a barrel  26 , a retractable tip  27  slidably mounted in the barrel  26 , a retaining annulus  28  and a spring  31  mounted between and acting between the lower surface of the retaining annulus  28  and the upper surface of the retractable tip  27 . The lower end of the barrel  26  is flanged inwardly and the upper portion of the retractable tip  27  is flanged outwardly such that the retractable tip  27  is maintained in the barrel  26 , but is free to slide up into the barrel  26  against the force of the spring  31 . The amount of travel allowed, however, is not unlimited. An annular stop  32  is positioned in the barrel to restrict the upward travel of the retractable tip  27  in the barrel  26 . Lenses  33 ,  34  are mounted in the retractable tip  27  of the objective  25 .  
         [0022]    Focusing of microscopes is generally accomplished by raising or lowering the stage relative to the objective. Some microscopes, however, are focused by raising and lowering the objective relative to a stage which is fixed to the frame, but the present invention works equally well, and in essentially the same manner, with such microscopes. Accordingly, reference will be made herein only to the moveable stage type microscopes.  
         [0023]    Unfortunately, the task of focusing a microscope is not error free. If the user believes that the microscope stage  12  needs to be raised in order to bring the sample into focus, the stage may be raised into contact with the objective. The user may not realize that the focus is being turned in the wrong direction because the image may be so out of focus that continuing to turn the coarse adjustment  22  or fine adjustment  23  in the wrong direction does not cause a change in the image that can be interpreted as further defocusing rather than as travel toward the proper focus point. Eventually, the retractable tip  27  may be retracted far enough to contact the annular stop  32 . At this point, any further turning of the coarse or fine adjustment  22 ,  23  can cause excessive pressure on the slide, which can break the slide  24 . This can result in several problems in addition to the slide breakage. First, the sample may be spoiled. This will require preparation of another sample, assuming additional sample material is available. Another problem that may result is that the tip of the objective and/or the lens may become contaminated.  
         [0024]    A preferred objective  35  according to one embodiment of the present invention is shown in FIG. 3. The present invention greatly reduces the risk of such problems by providing a simple, reliable, inexpensive method of detecting retraction of the retractable tip  37  into the barrel  35  and warning the microscope user before the retractable tip  37  reaches the annular stop.  
         [0025]    The objective  35  of the preferred embodiment comprises a barrel  36 , a retractable tip  37  slidably mounted in the barrel  36  and retained therein by an inward flange  36   a  at the lower end of the barrel  36 . The flange  36   a  cooperates with an outwardly-extending flange  37   a  on the retractable tip  37  to prevent the retractable tip  37  from sliding out of the lower end of the barrel  36 . A retaining annulus  38  is mounted toward the upper end of the barrel  36 , and a spring  41  is mounted between the annulus  38  and the upper surface of the retractable tip  37  to bias the retractable tip toward the lower end of the barrel  36 . Upward travel of the retractable tip  37  into the barrel  36  is limited by an annular stop  42  affixed to the interior of the barrel  36 . The lenses  43 ,  44  of the objective  36  are mounted in the retractable tip  37 .  
         [0026]    An activator tube  45  is mounted coaxially with the retractable tip  37  as by screw threads or pressing and extends upward therefrom. A lens or lenses could be mounted in the activator tube in addition to the lens or lenses  43 , 44  in the retractable tip  37 . The upper end of the activator tube  45  includes a flange  46 , the upper surface of which is reflective to infrared light. The tube  45  extends through the center opening of the retaining annulus  38  and is of a diameter that permits free movement therethrough when the retractable tip  36  is moved axially within the barrel  36 . The inside diameter of the activator tube  45  is sufficiently great that it does not interfere with the transmission of light along the light path between the lenses  43 ,  44  of the objective  35  and the eyepiece  21  of the microscope  10 .  
         [0027]    Referring next to FIGS. 1 and 3, the turret  18  of the microscope  10  includes the objective carrier  47  which is rotatably mounted to the upper, fixed portion of the turret  48 . Rotation of the objective carrier  47  moves the objectives  15 - 17  in turn into the light path.  
         [0028]    A sensor  51  is mounted to the fixed portion  48  of the turret  18  adjacent to the light path.  
         [0029]    This sensor  51  is preferably a reflective object sensor that includes an infrared light emitting diode (“ILED”) and a phototransistor mounted with their axes parallel to one another. Preferably, both the ILED and the phototransistor are contained in a single package that is opaque to visible light but which transmits infrared light. The devices are configured such that light does not shine directly from the ILED to the photo transistor. One such device is the sensor sold by Optek Technology, Inc. of Carrollton, Tex. under the model number OPB 608A. This sensor  51  is contained within an opaque housing and the ILED and phototransistor are encapsulated in a filtering epoxy which further reduces ambient light noise. The sensor  51  must be mounted sufficiently close to the objective carrier  47  portion of the turret  18  that it can sense the proximity of the flange  46  of the activator tube  45  when the activator tube  45  has been moved upward through the barrel  36  by upward movement of the retractable tip  37 .  
         [0030]    The activator tube  45  is sufficiently long and the flange  46  sufficiently broad that the sensor  51  will detect the proximity of the activator tube  45  before the retractable tip  37  of the objective  35  reaches the annular stop  42 . The activator tube, however, must not be so long as to contact any structure in the interior of the fixed portion  48  of the turret  18 , including the sensor  51 , which is mounted to the fixed portion  48  of the turret  18 .  
         [0031]    Some or all of the objectives  15 - 17  of the microscope may be equipped with activator tubes. The activator tubes may of necessity be of different lengths for different objectives, given differences in the length of the barrels  36 . It is important, however, that the length of the activator tubes  45  for each objective be chosen such that an alert can be issued before the associated objective has been retracted into the barrel  36  far enough to contact the annular stop  42 .  
         [0032]    The present embodiment of the invention is also highly desirable as no wires or other structure needs to protrude into the objectives  15 - 17  or from the fixed portion  48  of the turret  18  into the objective carrier. Further, there is no need for slip rings or other such connections in order to transmit power into the rotatable section of the turret  18  and its associated members.  
         [0033]    The sensor  51  is connected to a controller  52 , which, referring to FIG. 5, may include a microcontroller device. Of course, the sensor  51  function of the controller is to monitor the output of the sensor  51  and, upon the sensor  51  sensing the flange  46  of the activator tube, to output an alert, which may comprise an audio tone output via a speaker or buzzer or the extinguishing of the bulb  14 , or, preferably, both. FIG. 4 is an electrical schematic of a microcontroller operated circuit for practicing the invention. In the embodiment of the invention depicted in this figure is based on a microcontroller U 1  such as the model PIC16C71 microcontroller with analog-to-digital inputs sold by Microchip Technologies, Inc. of Chandler Ariz. This microcontroller U 1  incorporates the microprocessor, RAM and non-volatile memory onto a single integrated circuit, together with a plurality of analog to digital inputs. The microcontroller U 1  is connected to a timing crystal X 1  and associated electronics in a known manner, and to a terminal block S 2  which is in turn connected to a speaker and lamp dimmer potentiometer (not shown).  
         [0034]    Still referring to FIG. 4, power is applied to the system through terminal block S 1 , in which the alternating current power is applied to pins  1  and  2 . Pins  3  and  4  of the terminal block S 1  are connected to the lamp  14  in the illuminator system  13 . AC power flows from the terminal block S 1  to the full wave rectifier U 6 , and direct current is applied from the full wave rectifier U 6  to the 5V voltage regulator U 7 , which supplies regulated direct current power to the circuitry as indicated.  
         [0035]    An AC optoisolator U 4 B is connected across pins  1  and  2  of the terminal block S 1  to which the AC power is applied. This provides a signal to an analog input of the microprocessor U 1  for each zero volt crossing of the AC power. This signal is used to restart the logic sequence of the microcontroller U 1 .  
         [0036]    Potentiometer R 3  is connected to another analog input of the microcontroller U 1 . This potentiometer R 3  is also connected between the 5V DC power and ground circuitry and provides a sensitivity adjustment for the proximity detector circuitry.  
         [0037]    Optotriac U 3  is connected to an output of the microcontroller for operating the bulb. When a signal is received by the optotriac U 3  from the microcontroller U 1 , the optotriac U 3  triggers the triac U 5  to provide power to the bulb in the illuminator system  13 . In the absence of such signal from the microcontroller U 1  the optotriac U 3  and the triac U 5  reset when the AC power crosses zero volts.  
         [0038]    AC optoisolator U 4 A is connected across the bulb  14  of the illuminator system  13 , and is used to check whether the bulb  14  is on, and is connected to an input of the microcontroller U 1 . The proximity detector is connected to an analog input of the microcontroller U 1 .  
         [0039]    The software installed in the non-volatile memory of the microcontroller operates the circuitry in the following manner. Referring to FIG. 5, the microcontroller U 1  begins execution at the start  60 . The first step  61  is a loop in which the microcontroller continuously checks for receipt of a signal from AC optoisolator U 4 B indicative of a zero voltage crossing by the AC power applied to the circuitry. Upon receiving such a signal, the microcontroller U 1  executes the next step  62  of reading the digitized value of the signal output by the proximity detector  51 . This value is compared in the subsequent step  63  with a value generated from the analog input based on the setting of the adjustment potentiometer R 3  in the next step  64 .  
         [0040]    At this stage  64 , if the comparison value indicates that proximity of the surface  46  of the activator tube  45  has been detected, thus indicating that the trigger point has been reached, the microcontroller U 1  activates the speaker, and returns to the step  61  of looping until a zero volt crossing in the AC power is detected without activating the optotriac U 3  and hence without providing power to the lamp  14 .  
         [0041]    If the trigger point has not been reached, the microcontroller U 1  proceeds to the next step  66 . In this step  66 , a delay value is calculated based on a minimum delay value plus a delay value derived from the digitized value of the voltage received from the dimmer potentiometer (not shown) connected to the terminal block S 2 . This potentiometer is connected between the 5V DC power and ground and is adjustable in like manner to potentiometer R 3  to provide a selected voltage output to the microcontroller U 1 .  
         [0042]    The microcontroller U 1  uses this calculated value in the next step  67 . The microcontroller executes a delay loop based on the calculated value and decrements the value on each iteration of the loop until the value has been decremented to zero. At this stage, the microcontroller U 1  activates the optotriac U 3  which, in turn, activates the triac U 5  which supplies power to the lamp The optotriac U 3  and triac U 5  continue to provide power to the lamp until the next zero volt crossing of the AC power supplied to the system. As such, the greater the calculated value, the longer the delay will be before the lamp begins receiving power. The delay is calculated such that it is never more than one half of a power cycle of the AC power.  
         [0043]    Upon expiration of the delay cycle and activation of the optotriac U 3 , the program jumps back to the start  60  and commences the step of waiting for a zero voltage crossing in the AC power to the system.  
         [0044]    The sensor  51  of the preferred embodiment has been described herein as an infrared proximity detector device. Other devices, such as leaf springs, microswitches, break-beam sensors, magnetic and inductive proximity sensors, and pressure sensors might be used in lieu of the infrared proximity detector described herein all within the scope of the present invention. Of course, the use of different types of detectors may dictate changes in the configuration of the activator tube  45 . For example, a magnet might be attached thereto in the event that a magnetic proximity detector were used.