Patent Publication Number: US-2022225870-A1

Title: Ophthalmologic microscope with at least one controlled manual degree of freedom

Description:
TECHNICAL FIELD 
     The invention relates to an ophthalmologic microscope having a stand, a microscope device, at least a first and a second component manually movable in respect to each other, and a position sensor arranged to measure the relative position between the first and second components. 
     BACKGROUND ART 
     US 2011/0001931 describes a slit lamp microscope that can be manually moved, in respect to its stand, along two horizontal directions. 
     The device is equipped with electrically controlled brakes to brake any movements along these degrees of freedom. The user operates the brakes by actuating a switch on the device. 
     EP2721995 describes another slit lamp microscope having a setting-state acquiring part with a position sensor for measuring the angle of the illumination. 
     DISCLOSURE OF THE INVENTION 
     The problem to be solved by the present invention is to provide an ophthalmologic microscope of this type that has increased ease of use. 
     This problem is solved by the ophthalmologic microscope of claim  1 . 
     Accordingly, the ophthalmologic microscope comprises at least the following elements:
         A microscope device: The microscope device typically comprises a lens system for magnifying an image of the eye. It may further comprise a camera and/or an ocular.   At least a first component and a second component: These two components are manually movable in respect to each other, e.g. by being provided with a suitable linear or pivotal bearing between them.   A position sensor having a first sensor member arranged to measure a relative position between said first and second components: This first sensor member may e.g. include an angular or linear sensor. It generates an electronic signal indicative of the mutual position of the two components.   An electrically controlled brake. This brake comprises a primary brake member arranged between the first and second components.   A brake controller connected to the position sensor and the brake and adapted to operate the brake as a function of a reading of the position sensor.       

     This design of the microscope makes it possible to actuate the brake depending on the position of the two mutually movable components. Hence, even though the user can manually move the components, the device can assist in properly positioning them. 
     Advantageously, the “first component” is the base of the device or a stage translationally mounted to said base. 
     The “second component” may e.g. comprise the microscope or a light source of the microscope. 
     In an important application, the first and second component are pivotally movable in respect to each other. This is a common degree of freedom in the components of an ophthalmologic microscope, and it is expensive to motorize this degree of freedom. Hence, an assisted manual placement of the components provides great benefit to the user. 
     In an advantageous embodiment, the microscope comprises a third component, which may e.g. include a light source, manually movable in respect to the first component as well as to the second component. In this case, the brake comprises a secondary brake member arranged between the first and third component in order to generate an electrically controllable braking force between them. Further, the position sensor comprises a second sensor member arranged to measure the relative position between the first and third components. 
     The second sensor member can either make a direct measurement between the first and third component, or it may measure the relative position between the second and third component from which the relative position between the first and third component can be determined indirectly by combining it with the reading of the first sensor member. 
     The brake may further comprise two secondary brake members, with one secondary brake member arranged between the first and third component and the other secondary brake member between the second and third component. This allows to mutually fix any two of the three components to move them as a common unit against the remaining component. 
     The brake controller can be adapted to calculating the time to actuate the brake depending on a desired mutual position. In particular, the controller may comprise one or more storage positions for storing one or more desired brake positions. The current readings of the position sensor are compared to this brake position(s) in order to assist braking at these positions. 
     In order to improve braking accuracy, the brake controller may be further adapted to carry out the following steps:
         Determining the speed of motion between the components; and   Calculating the actuation time to actuate the brake depending on the desired mutual position and the speed of motion.       

     This allows an at least partial compensation of the speed-dependent braking distance of the microscope. 
     The brake controller may also be adapted to calculate the time delay between (1) actuating the brake and (2) the motion between the components coming to a standstill. This time delay can then be used to determine a more accurate actuation time for the brake. 
     As described below, this allows determining the state of the device and/or the manner in how it is used, which in turn helps to improve the timing of the braking process. In particular, the brake controller may be adapted to:
         Using a plurality of past measurements of braking processes to derive at least one parameter describing the braking distance of the brake.   Calculating the actuation time of the brake depending on this/these parameter(s).       

     Hence, the prediction of the braking distance can e.g. be adapted to the manual force a user employs to operate the device and/or to the state of the brake. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. This description makes reference to the annexed drawings, wherein: 
         FIG. 1  shows a lateral view of a slit lamp microscope, 
         FIG. 2  shows a top view of the microscope (with the slit lamp arm pivoted in respect to the microscope&#39;s optical axis), 
         FIG. 3  shows a sectional view of a hinge, and 
         FIG. 4  shows a block circuit diagram of some components of the brake controller. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     Overview 
       FIGS. 1 and 2  show an embodiment of an ophthalmologic microscope, in particular a slit lamp microscope. 
     The microscope has a base  1  resting e.g. on a desk, a translationally displaceable stage  2  mounted to base  1 , a first arm  3 , and a second arm  4 . 
     Stage  2  can be linearly displaced along horizontal directions x and z in respect to base  1 . 
     The arms  3  and  4  are mounted to stage  2  and pivotal about a common vertical pivot axis  5 , i.e. an axis parallel to vertical direction y. 
     Advantageously, arms  3  and/or  4  are manually operated, i.e. their angular position is changed manually, and they are not equipped with electric actuators for changing their angular positions. They may, however, also be provided with electric angular actuators to operate them automatically in addition to manually. 
     The device may further include a headrest  7  mounted to base  1  for receiving the patient&#39;s head. 
     Arm  3  carries a microscope device  8 , and arm  4  carries a light source  9 . 
     Microscope  8  has an optical axis  12 . It may comprise an entry objective  14 , which projects an image of eye  10  onto a camera  16  and/or an eyepiece  18 . A beam splitter  20  may be arranged to spilt light between these components. 
     Light source  9  may e.g. be a slit lamp as known to the skilled person, adapted to project a slit-shaped light beam onto the eye  10  to be examined. In the present embodiment, light source  9  comprises a light generator  22 , a spatial light modulator or adjustable mechanical slit  24 , and imaging optics  26 . 
     Light generator  22  can e.g. comprise several units emitting different wavelengths, e.g. in the red, green, blue, and infrared range of the optical spectrum. These units can be controlled separately in order to change the color of light source  22 . Imaging optics  26  projects the light from modulator  24  onto the anterior surface of eye  10 , e.g. via a mirror  28  mounted to arm  4 . 
     Light source  9  can be arranged above or below mirror  28 . 
     The device further comprises a hinge  30  connecting the arms  3  and  4  and stage  2  as well as a brake controller  32  for operating a brake of the device. 
     These components are described in more detail below. 
     Hinge Design 
       FIG. 3  shows a schematic sectional view of hinge  30  along pivot axis  5 . In this figure, parts with the same hatching style indicate parts that are rigidly connected to each other. 
     The purpose of Hinge  30  is to pivotally connect a first, a second, and a third component of the microscope to each other. In the present embodiment, the first component is stage  2 , the second component is first arm  3  with microscope device  8 , and the third component is second arm  4  with illumination source  9 . 
     These three components are pivotal in respect to each other about pivot axis  5 . 
     Hinge  30  comprises a “first hinge member”  32   a ,  32   b ,  32   c  rigidly connected to stage  2  (or base  1 ), i.e. to the first component of the microscope. 
     It further comprises a “second hinge member”  34  rigidly connected to arm  3 , i.e. to the second component of the microscope. 
     It also comprises a “third hinge member”  36   a - 36   d  rigidly connected to arm  4 , i.e. to the third component of the microscope. 
     For an embodiment of the invention where the components are pivotal, the term “rigidly” connected is to be understood as “non-pivotally” connected. 
     Hinge  30  further comprises a brake having a primary brake member  38   a  and one or two secondary brake members  38   b ,  38   c.    
     Primary brake member  38   a  comprises a first coil member  40   a  and a first brake disk  42   a , which are arranged to generate a frictional braking force between the first hinge member  32   a - 32   c  and the second hinge member  34 . 
     In the embodiment shown, first coil member  40   a  is connected to first hinge member  32   a - 32   c  and first brake disk  42   a  is connected to second hinge member  34 , even though the opposite arrangement can be used as well. 
     Secondary brake member  38   b  comprises a second coil member  40   b  and a second brake disk  42   b , which are arranged to generate a frictional braking force between the second hinge member  34  and the third hinge member  36   a - 36   d.    
     In the embodiment shown, second coil member  40   b  is connected to second hinge member  34  and second brake disk  42   b  is connected to third hinge member  36   a - 36   d , even though the opposite arrangement can be used as well. 
     Secondary brake member  38   c  comprises a third coil member  40   c  and a third brake disk  42   c , which are arranged to generate a frictional braking force between the first hinge member  32   a - 32   c  and the third hinge member  36   a - 36   d.    
     In the embodiment shown, third coil member  40   c  is connected to first hinge member  32   a - 32   c  and third brake disk  42   d  is connected to third hinge member  36   a -  36   d , even though the opposite arrangement can be used as well. The brake members  38   a ,  38   b ,  38   c  can be actuated individually and independently. 
     The coil members  40   a ,  40   b ,  40   c  as well as brake disks  42   a,    42   b ,  42   c  are advantageously annular and coaxially arranged round pivot axis  5 . 
     The brake disks  42   a,    42   b,    42   c  are of a ferroelectric material, and they are attracted to their respective coil member  38   a,    38   b,    38   c  when a current is sent through the latter. In the shown embodiment, this attraction generates a frictional force that brakes the motion between the two respective hinge members. 
     Hinge  30  further comprises a primary pivotal bearing  44   a  pivotally connecting first hinge member  32   a - 32   c  and second hinge member  34 . Its rotation axis coincides with pivot axis  5 . 
     Hinge  30  also comprises two secondary pivotal bearings  44   b,    44   c . Secondary pivotal bearing  44   b  connects second hinge member  34  to third hinge member  36   a - 36   d,  and secondary pivotal bearing  44   c  pivotally connects first hinge member  32   a - 32   c  to third hinge member  36   a    36   d.  The secondary pivotal bearings  44   b ,  44   c  are again coaxial to pivot axis  5 . 
     Hinge  30  further comprises a position sensor with a first and a second sensor member  46   a,    46   b.    
     First sensor member  46   a  is arranged between first hinge member  32   a - 32   c  and second hinge member  34 . It is adapted to measure the relative pivotal position between these two hinge members. 
     Second sensor member  46   b  is arranged between first hinge member  32   a - 32   c  and third hinge member  36   a - 36   d.  It is adapted to measure the relative pivotal position between these two hinge members. 
     The first and second sensor members  46   a,    46   b  may be magnetic angular position sensors. 
     In the embodiment of  FIG. 3 , the first component of the microscope, i.e. stage  2  and/or base  1 , is connected to a first location of hinge  30  (the lower end of hinge  30  in  FIG. 3 ). The second component of the microscope, i.e. arm  3  and microscope device  8 , is mounted to a second location of hinge  30  (the mid-section of the hinge in  FIG. 3 ). The third component of the microscope, i.e. arm  4  and light source  9 , is mounted to a third location of hinge  30  (the top end of the hinge in  FIG. 3 ). 
     The second location is located, along pivot axis  5 , between the first and third location. When using this type of design, the first hinge member  32   a - 32   c  or the third hinge member  36   a - 36   d  advantageously comprises a shaft extending through the second hinge member  34 , which allows the first and third hinge members to interact directly. 
     In the embodiment of  FIG. 3 , this shaft  36   c  is formed by the third hinge member, which allows mounting secondary brake member  38   c  and/or second sensor member  46   b  at the first location of hinge  30 . 
     In other words, the shaft is connected, at one side, to the first or third component of the microscope and, at the other side, to one of the brake members and/or sensors members. 
     Shaft  36   c  is hollow and can receive cabling, e.g. connected to the brake members  38   a - 38   c,  to microscope device  8 , and/or to light source  9 . 
     In the embodiment shown, the pivotal bearings  44   a,    44   b,    44   c  are roller bearings. Such roller bearings have very low friction when the brake is deactivated. This may not always be desirable. Hence, one or more frictional dampers  45   a ,  45   b  can be provided for damping the movement between at least one pair of the components. 
     The frictional damper(s) is/are designed to exert a permanent frictional force between the components, which is much larger than the roll resistance of the roller bearings, in particular at least 100 times larger. 
     In the embodiment shown, a first frictional damper  45   a  is provided for damping the movement between the first and second component, and a second frictional damper  45   b  is provided for damping the movement between the first and third component. 
     In more general terms, the device comprises the combination of at least one roller bearing and at least one frictional damper between at least two of the components. 
     Advantageously, there is a roller bearing  44   a  and a frictional damper  45   a  between the first and second component, and there is a roller bearing  44   c  and a frictional damper  45   b  between the first and third component. In a particularly advantageous embodiment, there is a roller bearing  44   b  but no frictional damper between the second and third component, which makes it easier to move the second or third component in respect to the first component without moving the third or second component, respectively. 
     Brake Operation 
     The microscope comprises a brake controller  50 , which is schematically illustrated in  FIG. 4 . 
     It may comprise a microcontroller or microprocessor, which can e.g. be part of the control unit of the microscope. It is programmed to carry out the various brake functions described below. 
     Brake controller  50  is connected to the position sensor, i.e. to the sensor members  46   a,    46   b,  which allows it to determine the current mutual positions of the three microscope components. 
     It is also connected to the brake members  38   a,    38   b,    38   c  to operate them. 
     Brake controller  50  is further connected to a display  52  adapted to show operating instructions and/or status information to the user. 
     In the following, we describe some functionalities that may be implemented in brake controller  50 . 
     Actuation Time 
     A first functionality relates to supporting the user in moving the components of the microscope to a certain predefined mutual position. 
     In this functionality, a storage section  54  of brake controller  50  may hold at least one “desired mutual position” between two of the components of the microscope. 
     Brake controller  50  may now be equipped to compare this desired mutual position to the current mutual position between the two components. If there is a mismatch between the two, brake controller  50  displays, on display  52 , the direction of displacement for moving one of the components to the desired mutual position. 
     For example, the desired mutual position may e.g. be an angle of 37.2° between stage  2  and first arm  3 . First sensor member  46   a  e.g. indicates the current mutual position, i.e. the current angle, to be 33.5°. One or both of these numbers may be shown on display  52 . 
     Next, brake controller  50  determines the direction to move arm  3  from its current position to the desired position. This direction is then displayed e.g. by highlighting one of two arrows  56   a,    56   b  on display  52 . 
     By displaying the direction of displacement in this manner, the user is assisted to manually move one of the components into the right direction. 
     Brake controller  50  may then assist the user further in properly braking the component being moved at the right time in order to stop the movement at the desired position. To do so, it calculates the time to actuate the brake, i.e. at least one of its brake members  38   a,    38   b,    38   c.    
     In a most simple approach, the actuation time to activate the brake may be the one where the current position matches the desired position. This may, however, lead to a poor match because the brake has a certain braking distance and may therefore come to a halt at a position beyond the desired position. 
     A more accurate algorithm takes the speed of motion between the two components into account. 
     Let us assume that x0 is the desired mutual position and x(t) is the current mutual position. In that case, the actuation time t0 for actuating the brake should be the one where x0-x(t0) equals the expected braking distance D of the microscope, i.e. 
     
       
         
           
             
               
                 
                   
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     Braking distance D is not a constant. Rather, it is typically a function of the current speed v(t)=dx(t)/dt of the motion and the reaction time Δt of the brake. It may also be a function of the force with which the user moves the component (a strong force may add to the braking distance). Hence 
     
       
         
           
             
               
                 
                   
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     with u being a user-dependent parameter 
     In a specific example, braking distance D may be approximated by 
     
       
         
           
             
               
                 
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     The speed v in Eq. (2, 3) can be calculated from the measurements of the position sensor  46   a,    46   b.  The parameters At and u may be obtained in various manner:
         The time delay At may be considered to be a device-specific delay, which can e.g. be obtained from calibration measurements at the manufacturer&#39;s site. However, it may vary over time, e.g. due to attrition or contamination of the brake, and it is therefore advantageously derived from prior braking processes as described below.   The parameter u can be assumed to be constant and be determined from calibration measurements at the manufacturer&#39;s site with a sample of typical users. However, since it depends on how a given user operates the device, it is best also derived from prior braking processes (advantageously carried out by the same user as the one currently using the microscope) as described below.       

     If one or more of the parameters Δt, u is to be derived from previous braking processes, brake controller  50  is advantageously adapted to carry out the following steps:
         Measuring, for a plurality of past braking processes, the braking distance D and the speed v(t0) upon actuating the brake.   Storing the braking distances and velocities obtained in this manner.   Using a model for the braking distance D(Δt, v, u) as a function of the speed v(t0) having the unknown parameter(s) as model parameter(s) and fitting these model parameter(s) to the stored braking distances and velocities.       

     Depending on the model used for the braking distance D(Δt, v, u) as a function of the speed v(t0), it is e.g. possible to use a linear fitting algorithm (e.g. for the model of Eq. (3)) or a non-linear fitting algorithm. 
     If at least one parameter, such as parameter u, is to be varied between user and user, brake controller  50  is equipped with a suitable input means  58  for entering a user-specific ID. In that case, brake controller  50  determines different sets of parameters for the different users. 
     The determination of one or more parameters can e.g. be refined automatically after each braking process. 
     Releasing the Brake 
     The brake may be released manually, e.g. by providing a brake release input  60 , such as a button or an area on a touchscreen. When the user operates this input, the brake is released. 
     In another embodiment, brake controller  50  may be adapted to carry out the following steps: 
     a) Detecting, while having activated the brake  38   a,    38   b,    38   c,  an increase of a force acting against the brake  38   a,    38   b,    38   c.    
     b) Upon such an increase, releasing the brake  38   a,    38   b,    38   c.    
     In this manner, the user may simply push one of the components against the force of the brake, in which case the brake is released. 
     Step a) and or b) may be suppressed for a given time, e.g. 1 second, after actuating a brake, or be suppressed while the component has not yet come to a standstill, in order to make sure that the force is an intentional effort to move the component away from its position after a completed braking process. 
     The detection of step a) may e.g. be carried out by means of a dedicated force sensor. However, if position sensor  46   a,    46   b  is of sufficient resolution, it can be used to detect an elastic deformation in hinge  30  due to the force applied to the component(s), so it can be used to detect the force without the need for a dedicated force sensor. 
     Haptically Marking Positions 
     The brake can also be operated only briefly, in a “tapping” operation, while the user moves one of the components. This will generate a haptic feedback for the user that marks certain preferred mutual positions of the components, such as an axial alignment or an alignment under certain angles. 
     In order to implement this, brake controller  50  may be adapted to activating and automatically deactivating the brake  38   a,    38   b,    38   c  for a duration of less than 1 second, in particular of less than 0.5 seconds. On the other hand, the activation duration is advantageously at least 0.1 seconds because much slower activations may not be sufficient to generate a breaking effect the user can act upon. 
     The duration may e.g. be given as follows:
         It may be a fixed time.   It may depend on the signal from the position sensor  46   a,    46   b.  If, for example, brake controller  50  detects that the speed v(t) drops quickly after actuating the brake (e.g. by more than a given percentage in a given time), it can keep the brake activated, assuming that the user has released the component and wants to stop at this location. Otherwise, it releases the brake, assuming that the user has not released the component, does not want to stop at the given position, and wants to continue moving the component.       

     Such haptic feedback implemented by temporarily actuating the brake may eliminate the need for mechanical feedback members, such as mechanical indexing mechanisms. 
     Group Operation 
     Brake controller  50  may further be equipped for grouping two of the three components into a group while letting the remaining component free to move relative to the group. 
     For example, brake controller  50  may be adapted to operate the brake  38   a,    38   b,    38   c  in at least one, in particular at least two, of the following modes:
         Actuating first brake member  38   a  while deactivating second brake member  38   b  and third brake member  38   c.  In this case, the mutual position of the first and the second components (base  2  and arm  3  in the embodiment of  FIG. 3 ) is kept fixed while the third component (arm  4 ) can be moved.   Actuating second brake member  3   8   b  while deactivating first brake member  38   a  and third brake member  38   c.  In this case, the mutual position of the second and third components (arms  3  and  4 ) is fixed, and the two can be moved as a group in relation to the first component (base  2 ).   Actuating third brake member  38   c  while deactivating first brake member  38   a  and second brake member  38   b.  In this case, the mutual position of the first and third components (base  2  and arm  4 ) is fixed, while the second component (arm  3 ) can be moved relation to them.       

     In other words, brake controller  50  may be adapted to keep one brake member activated while keeping the two other brake members deactivated, and, advantageously, the user may chose the brake member to be activated. 
     Notes 
     In the shown embodiment, the brake members are brought into their braking state by feeding a current through them. In other words, if the microscope is without current, the brake is released. This allows for a compact design of the device and/or reduces power consumption in the non-braking state. 
     In another embodiment, the brake members may be designed such that they are brought into their non-braking state by sending an electric current through them. This can e.g. be achieved by brake members having two rings urged against each other by a spring member, with an electromagnet that can be activated to act against the force of the spring. This design allows locking the microscope in the unused state in the absence of a current, and it reduces power consumption in the braking state. 
     In the embodiment above, there are three mutually movable components. The microscope may, however, also comprise only two mutually movable components, or it may comprise more than three of them. 
     In the shown examples, the components are pivotal in respect to each other, and the brake is adapted to brake the pivotal movement between the components. However, the invention may also be used for other types of relative displacement. It may e.g. be used to brake a linear displacement between components of the microscope, such as the displacement of stage  2  in respect to base  1  in the directions x and/or z or a vertical displacement of a component along direction y, such as a vertical displacement of headrest  7 . 
     The microscope described here assists the user in properly aligning the various components, e.g. in order to establish or reproduce a desired measurement configuration. 
     While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.