Abstract:
A potentiometer is disclosed which comprises an opaque screen element ( 10 ) and light emitters and collectors ( 92 ) for transmitting light through the screen and detecting the light transmitted through the screen. The screen has three sections (A, V and B). The sections (A, V and B) have bars which are parallel to one another and extend transverse to the direction of movement of the screen ( 10 ). The section (A) has bars which are arranged in groups comprising the same number of bars, but each of a different thickness. The section (V) has two parts ( 35, 36 ), the first part has bars which are formed in the same manner as the section (A) except they are a mirror image to the bars in section (A) and each group comprises less bars than are in the groups in section (A). The second part of section (V) has individual bars which increase in thickness. Section (B) is a mirror image of section (A). This configuration allows for any drifting of voltage indicative of a change in light intensity which is detected by the emitter to be identified and compensated for because the intensity of light passing through the sections and plotted against position forms a U or V-shaped profile, with the apex identifying the maximum or minimum light intensity and therefore voltage at the collector.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a potentiometer and, in particular, but not exclusively, to a potentiometer for a control lever assembly for use in boats. The invention is an improvement to the potentiometer disclosed in our International Patent Application No. PCT/AU2005/001608 and corresponding Australian Provisional Patent Application Nos. 2004907143 and 2005904019. The contents of these applications are incorporated into this specification by this reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    As explained in the above International application, conventional potentiometers generally comprise variable resistors. These types of potentiometers do suffer from a number of problems. The invention in our above International application provides an optical potentiometer which addresses the disadvantages of potentiometers which comprise variable resistors. 
         [0003]    The potentiometer disclosed in our International application does operate extremely well but there is still room for further improvement in relation to the sensitivity of the potentiometer and the manner in which redundancy is provided to ensure that the potentiometer continues to operate. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention, in a first aspect, may be said to reside in a potentiometer comprising:
       a light emitter device;   a light collector device;   a screen element located between the emitter device and collector device for movement relative to the emitter device and collector device;   the screen element having at least a first section and a second section;   the first section allowing the amount of light which can pass through the first section to change from a first location of the first section to a second location of the first section; and   the second section having a first part and a second part, the first part allowing the amount of light which can pass through the first part to change from a first location of the second section to an intermediate location of the second section, and the second part allowing the amount of light which can pass through the second part to change from the intermediate location to a second location of the second part, the change in the amount of light which can pass through the first part, varying from a first one of a maximum and minimum intensity at the first location to the other of the maximum and minimum intensity at the intermediate location, and the intensity of the light which passes through the second part varying from one of a maximum and minimum intensity at the intermediate part to the other of the maximum and minimum at the second location.       
 
         [0011]    Thus, according to this aspect of the invention, the relative amount of light which passes through the second part from the first location of the second part to the second location of the second part plotted against position of the second section from the first location to the second location, is of V or U-shaped configuration. The apex of the V or U thereby providing a minimum or maximum point which can be used to readily identify a reference location such as, in the case of a boat control, a neutral drive lever position. Because this position is at a maximum or minimum, any drift due to temperature or the like can be easily compensated for because the apex will always be a maximum or minimum, notwithstanding that the actual voltage level corresponding to the light intensity may change slightly with temperature fluctuation. Thus, the neutral position can always be easily ascertained. The amount of light which passes through the first section enables a determination to be made as to which side of the apex the light intensity reference is so that a control signal relative to the minimum or maximum can be generated. Thus, in terms of a boat controller, one side of the apex of the plot can relate to forward gear and the other side of the V or U-shape plot relative to the apex indicating reverse gear. 
         [0012]    In the preferred embodiment of the invention the first part is longer than the second part. This provides greater sensitivity in the first part and in terms of a boat control, the first part can be used to indicate forward gear in which the boat will spend most of its time, thereby providing greater sensitivity and speed range in forward gear, than in reverse gear where the boat will spend less time and usually will be required to move much slower. 
         [0013]    Preferably the screen element has a third section and the amount of light which can pass through the third section of the screen element varying from a first position of the third section to a second position of the third section. 
         [0014]    Most preferably the third section is a mirror image of the first section. 
         [0015]    Preferably the screen element comprises a variable translucency screen element so that light is able to pass through the screen element from the light emitter device to the light collector device. 
         [0016]    Preferably the variable translucency of each section of the screen element is defined by a plurality of spaced apart bars of varying size which are perpendicular to the direction of relative movement between the screen element and the emitter device and collector device. 
         [0017]    Most preferably the bars in the first section comprise groups of bars of different width, each group having a plurality of bars of the same width. 
         [0018]    Preferably the first part of the second section comprises groups of bars with each group having a plurality of bars of a lesser number than those in the groups of the first section. 
         [0019]    Preferably the second part of the second section comprises individual bars of varying width. 
         [0020]    Preferably the screen element has a diffuser on both sides of the screen element. 
         [0021]    Preferably the screen element is of cylindrical configuration. 
         [0022]    Preferably the light emitter device comprises a separate light emitter for each of the sections of the screen element and the light collector device comprises a separate light collector for each section for collecting light from the corresponding light emitter. 
         [0023]    Preferably the screen element is mounted for movement and the light emitter device and light collector device are stationary. 
         [0024]    The present invention, in a second aspect, may be said to reside in a potentiometer comprising:
       a light emitter device;   a light collector device;   a screen element located between the emitter device and collector device for movement relative to the emitter device and collector device; and   a plurality of bars on the screen element to provide varying translucency of the screen element, the plurality of bars being arranged in groups with each group having a plurality of individual bars of the same thickness, and the thickness of bars in respective groups of bars being different from one another.       
 
         [0029]    Thus, according to this aspect of the invention, because groups of bars are provided with each group having bars of the same thickness, but the respective groups having bars of different thickness, a relatively long length of screen element can be provided within the confines of limitations provided by forming the bars on the screen element, to thereby provide greater sensitivity of the potentiometer. The greater sensitivity is achieved by enabling the length from a minimum thickness of the bars to a maximum thickness of the bars to be increased because of the plurality of bars in each group. 
         [0030]    Preferably the screen element has at least a first section and a second section;
       the first section allowing the amount of light which can pass through the first section to change from a first location of the first section to a second location of the first section; and   the second section having a first part and a second part, the first part allowing the amount of light which can pass through the first part to change from a first location of the second section to an intermediate location of the second section, and a second part in which the amount of light which can pass through the second part changes from the intermediate location to a second location of the second part, the change in the amount of light which can pass through the first part, varying from one of a maximum and minimum intensity at the first location to the other of the maximum and minimum at the intermediate location, and the intensity of the light which passes through the second part varying from the other of the maximum or minimum at the intermediate part to the other of the maximum and minimum at the second location.       
 
         [0033]    Preferably the screen element has a third section and the amount of light which can pass through the third section of the screen element varying from a first position of the third section to a second position of the third section. 
         [0034]    Most preferably the third section is a mirror image of the first section. 
         [0035]    Preferably the bars are perpendicular to the direction of relative movement between the screen element and the emitter device and collector device. 
         [0036]    Most preferably the bars in the first section comprise groups of bars of different width, each group having a plurality of bars of the same width. 
         [0037]    Preferably the first part of the second section comprises groups of bars with each group having a plurality of bars of a lesser number than those in the groups of the first section. 
         [0038]    Preferably the second part of the second section comprises individual bars of varying width. 
         [0039]    Preferably the screen element has a diffuser on both sides of the screen element. 
         [0040]    Preferably the screen element is of cylindrical configuration. 
         [0041]    Preferably the light emitter device comprises a separate light emitter for each of the sections of the screen element and the light collector device comprises a separate light collector for each section for collecting light from the corresponding light emitter. 
         [0042]    Preferably the screen element is mounted for movement and the light emitter device and light collector device are stationary. 
         [0043]    The invention in a still further aspect may be said to reside in a potentiometer comprising:
       a light emitter device;   a light collector device;   a screen element located between the light emitter device and the light collector device for movement relative to the light emitter device and light collector device; and   a diffuser for diffusing light before or after the light passes through the screen element.       
 
         [0048]    This aspect of the invention results in a more consistent change of the amount of light which passes through the screen element, thereby overcoming slight irregularities in the intensity detected by the light collector, and therefore providing a better control signal from the potentiometer. 
         [0049]    Preferably the light diffuser comprises a first diffuser element on one side of the screen element, and a second diffuser element on the other side of the screen element. 
         [0050]    Preferably the first and second diffuser elements comprise a housing for retaining the screen element. 
         [0051]    Preferably the screen element has at least a first section and a second section;
       the first section allowing the amount of light which can pass through the first section to change from a first location of the first section to a second location of the first section; and   the second section having a first part and a second part, the first part allowing the amount of light which can pass through the first part to change from a first location of the second section to an intermediate location of the second section, and a second part in which the amount of light which can pass through the second part changes from the intermediate location to a second location of the second part, the change in the amount of light which can pass through the first part, varying from one of a maximum and minimum intensity at the first location to the other of the maximum and minimum at the intermediate location, and the intensity of the light which passes through the second part varying from the other of the maximum or minimum at the intermediate part to the other of the maximum and minimum at the second location.       
 
         [0054]    In the preferred embodiment of the invention the first part is longer than the second part. 
         [0055]    Preferably the screen element has a third section and the amount of light which can pass through the third section of the screen element varying from a first position of the third section to a second position of the third section. 
         [0056]    Most preferably the third section is a mirror image of the first section. 
         [0057]    Preferably the screen element comprises a variable translucency screen element so that light is able to pass through the screen element from the light emitter device to the light collector device. 
         [0058]    Preferably the variable translucency of each section of the screen element is defined by a plurality of spaced apart bars of varying size which are perpendicular to the direction of relative movement between the screen element and the emitter device and collector device. 
         [0059]    Most preferably the bars in the first section comprise groups of bars of different width, each group having a plurality of bars of the same width. 
         [0060]    Preferably the first part of the second section comprises groups of bars with each group having a plurality of bars of a lesser number than those in the groups of the first section. 
         [0061]    Preferably the second part of the second section comprises individual bars of varying width. 
         [0062]    Preferably the screen element has an opaque cover on both sides of the screen element. 
         [0063]    Preferably the screen element is of cylindrical configuration. 
         [0064]    Preferably the light emitter device comprises a separate light emitter for each of the sections of the screen element and the light collector device comprises a separate light collector for each section for collecting light from the corresponding light emitter. 
         [0065]    Preferably the screen element is mounted for movement and the light emitter device and light collector device are stationary. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0066]    A preferred embodiment of the invention will be described, by way of example, with reference to the accompanying drawings, in which: 
           [0067]      FIG. 1  shows the layout of a screen element used in the preferred embodiment of the invention; 
           [0068]      FIG. 2  is a graph of transmitted light intensity versus position in respect of the screen element described with reference to  FIG. 1 ; 
           [0069]      FIG. 3  is a view of an outer diffuser used in the preferred embodiment; 
           [0070]      FIG. 4  is a view of the screen element of  FIG. 1  formed into a cylindrical shape; 
           [0071]      FIG. 5  is a view of an inner diffuser used in the preferred embodiment; 
           [0072]      FIG. 6  is a view of a light emitter and collector arrangement used in the preferred embodiment; 
           [0073]      FIG. 7  is a view of the assembled potentiometer; and 
           [0074]      FIG. 8  is a view of the potentiometer associated with a control lever for a boat. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0075]    With reference to  FIG. 1  a screen element  10  is shown which has a first section marked band A, a second section marked band V and a third section marked band B in  FIG. 1 . Each of the sections are provided with printed bars which are parallel with respect to one another and perpendicular to the direction of relative movement of the screen element  10  with respect to light emitters and collectors  92  which will be described with reference to  FIGS. 6 and 7 . Suffice it to say for the present purpose that in the preferred embodiment of the invention, one light emitter and one light collector is associated with each of the sections A, V and B as shown in  FIG. 7 . The parallel bars have centres which are spaced from one another by the same distance and are of different width to provide varying translucency because the space between edges of the bars will therefore decrease as the bars become thicker. Thus, the amount of light which is detected by the collector changes as the screen  10  moves relative to the emitters and collectors. The use of parallel bars as shown in  FIG. 1  is advantageous because any movement of the screen element in the direction of double-headed arrow D in  FIG. 1  relative to the light emitters and light collectors will have no consequence on the amount of light which is transmitted. Thus, any slight relative movement of parts of the potentiometer after assembly and in use will not create any errors because the movement will not alter the light intensity which passes through the screen element  10 . 
         [0076]    In the preferred embodiment of the invention, three sections are utilised so as to provide an output reference signal which can be used to show that a boat control lever L (see  FIG. 8 ) is in neutral, or in forward gear to give a required forward speed, or in reverse gear to give a required reverse speed, as well as providing signals which can be used to distinguish between reverse and forward gear, and also providing some redundancy in case some of the light emitters or collectors should fail during operation. 
         [0077]    In the preferred embodiment shown in  FIG. 1 , the section V provides the control signal to provide boat speed and to select neutral. The section A enables forward gear and reverse gear to be distinguished and the third section B provides for redundancy. 
         [0078]    The first section A is formed from a plurality of groups of bars with each group having three bars of the same thickness. For example, in the enlarged circle part of section A shown in  FIG. 1 , there are three bars  12  of the same thickness, then three bars  14  of larger thickness and then three bars  16  of still larger thickness. Each of the bars  12  are of the same thickness, each of the bars  14  are of the same thickness, and each of the bars  16  are of the same thickness. The reason for providing multiple bars of the same thickness in each group  12 ,  14  and  16 , etc. is to ensure that the length of the section from a first location  20  to a second location  30  can vary over a relatively long distance of the screen element  10  (for example 120°) when the screen element  10  is formed into a cylinder, as shown in  FIG. 4 . 
         [0079]    In the preferred embodiment of the invention the bars  12  are formed by printing and the greatest sensitivity which can be provided is a bar of width 0.02 mm. The bars can then be increased in thickness by doubling that thickness. For example, the bars  12  may start at the second location  30  and be of 0.2 mm thickness, the bars  14  are of 0.04 mm thickness, the bars  16  of 0.06 mm thickness and so on from the position  30  to the position  20 . If only a single bar  12 ,  14 ,  16  of one thickness is provided, the distance between the first and second locations  20  and  30  using the same graduation would be much smaller (and indeed, ⅓ the distance which is provided by using three bars of the same width in each group). The smaller distance would thereby greatly reduce sensitivity because light intensity change would go from a maximum to a minimum in a much smaller distance than if multiple bars of the same thickness are used as shown in  FIG. 1 . 
         [0080]    Section V of the screen element  10  has a first part  35  and a second part  36 . The first part  35  has a first location  31  and extends to an intermediate location  32  of the section V. The second part  36  extends from the intermediate location  32  to a second location  33 . The first part  35  is formed in the same manner as the first section A, except that each group of bars comprises two bars, such as a first group of bars  42 , a second group of bars  44 , and a third group of bars  46 , etc. The bars are formed of multiple thicknesses of 0.02 mm. The section V is the same length as the section A and also occupies 120° of the cylindrical screen element  10  shown in  FIG. 4 . However, because the groups of bars in the first part  35  comprise two bars instead of three bars, the length of the first group is effectively two thirds of the length of the section V. The second part  36  is formed of individual bars  47 ,  48  and  49  (for example) which increase in thickness by multiples of 0.02 mm and has a length of ⅓ of the section V. 
         [0081]    As is shown in the enlarged detail in  FIG. 1 , the bars in the first part  35  increase from a minimum thickness at the first location  31  to a maximum thickness at the intermediate location  32 . The bars in the second part  36  decrease from the maximum thickness at the intermediate location  32  to a minimum thickness at the second location  33 . 
         [0082]    As is shown in  FIG. 2 , when the screen element  10  moves relative to the light emitter and light collector, the light intensity transmitted through the screen element  10  from position  31  shown in  FIG. 2  to position  33  changes in a V-shaped profile. Thus, the electric control signal which is provided from the collector is of V-shaped profile  50  as shown in  FIG. 2 . The apex  51  of the signal  50  is of course a minimum and therefore the apex which provides neutral position in the case of the boat control lever L, can always be determined because it is the minimum voltage signal from the light collector. Thus, even if the voltage change slightly because of changes in temperature or other fluctuations, the minimum voltage can always be determined as the lever moves between positions  31  and  33  so that neutral position can always reliably be obtained. 
         [0083]    In an alternative embodiment, rather than having the maximum bar thickness at the intermediate position  32 , the bars in the first part  35  and the second part  36  can be reversed so that the minimum thickness bars are at the intermediate position  32 . This would mean that the V-shaped profile  50  is in effect inverted in shape to that shown in  FIG. 2 . Nevertheless, the same advantages are derived. 
         [0084]    The third section B of the screen element  10  is a mirror image of the first section A, with the minimum bar thickness being at a first location  37  and the maximum bar thickness being at the second location  38 . Once again, if desired, the location of the maximum thickness bars and minimum thickness bars in the sections A and B could be reversed to that shown in  FIG. 1 . 
         [0085]    When light passes through the section A, a light intensity variation  60  shown in  FIG. 2  is provided, and when light passes through the section B, a light intensity variation  62  shown in  FIG. 2  is provided. 
         [0086]    Thus, if the boat control lever L is moved to provide forward motion to in turn the screen element  10  relative to the respective light emitters and light collectors, to a position, for example P shown in  FIG. 2 , an output voltage V 1  from the light collector associated with the section V is obtained. However, it is not possible to determine whether that voltage V 1  corresponds to forward motion, which is the part of the trace  50  labelled  50 ′ in  FIG. 2 , or reverse motion which is the part of the trace  50 ″ in  FIG. 2 , because a lever position at P 1  shown in  FIG. 2  will also provide the same voltage output from the collector associated with section V. Thus, to determine whether the position of the lever is in fact P or P 1 , the voltage outputs from the light collectors associated with the section A or section B are considered. The voltage output V 0  from the light collector associated with section A is matched with the voltage V 1  to determine the part of the V-shaped trace that applies (in other words, forward gear is selected). For example, at position P, voltage V 1  is matched with the voltage from the collector associated with band A and if that voltage is V 0 , then the system knows that the forward gear trace  50 ′ is that which applies. If the voltage was V 2 , then the reverse gear trace  50 ″ would apply. Thus, if the voltage V 1  matches a voltage in the range Va to Vb, then forward gear and trace  50 ′ is applicable. If the voltage V 1  matches a voltage of Vb to Vc, then the trace  50 ″ is applicable and reverse gear is that which is selected. 
         [0087]    As is shown in  FIGS. 1 and 2 , the part  35  is greater than the part  36  so that more sensitivity is provided in forward gear where the boat will spend most of its time and usually require a greater speed range than reverse gear, where the boat will spend much less time and generally require much less speed range. However, if desired, the parts  35  and  36  could be the same size and, further still, if reverse gear is more important, the part  36  could be larger than the part  35 . 
         [0088]    The third section B provides redundancy in case the light emitter or collector associated with section A fails or, in fact, the light emitter or light collector associated with section V fails. The output signal from the light collector associated with section B can be used to determine which side of the apex  51  is involved, in the same manner as previously described. The light collectors associated with the sections A and B can also provide appropriate control if the light emitter or collector associated with section V fails, to enable the boat to be controlled in speed. The combination of the voltages from the collectors associated with sections A and B will enable a determination to be made as to whether reverse or forward gear is selected and the appropriate speed based on the levels of those voltages. 
         [0089]    Thus, the preferred embodiment of the invention described with reference to  FIGS. 1 and 2  provides considerable sensitivity to the control of the speed and the determination of whether forward or reverse gear has been selected, and also redundancy in case there is some failure in the light collectors or emitters or associated circuitry during use of the potentiometer. 
         [0090]      FIG. 3  to  FIG. 7  show the assembly of the potentiometer according to the preferred embodiment.  FIG. 3  shows an outer diffuser which simply comprises a transparent ring  80  which has been provided with a fusing surface so that light diffuses slightly as it passes through the diffuser  80 .  FIG. 4 , as previously mentioned, shows the screen  10  of  FIG. 1  formed into a cylindrical configuration. 
         [0091]      FIG. 5  shows an inner diffuser  82  which is of cap-shaped design having a peripheral wall  84  and a top  86 . The cylindrical strip  10  locates on the peripheral wall  84  and then the outer diffuser  80  locates over the strip  10 . Thus, a diffuser is provided on both sides of the screen element  10  for diffusing light which passes through the screen element  10  so as to provide a more stable light variation and less irregularities or peaks and troughs in the output voltages from the respective light collectors. 
         [0092]      FIG. 6  shows a circuit board  90  on which is mounted circuitry for operating the potentiometer, including three sets of light emitters and light collectors  92 . Each set of light emitters and light collectors corresponds to one of the sections A, V and B shown in  FIG. 1 . The peripheral wall  84 , with the screen element  10  and the outer diffuser  80 , locates between respective light emitters  92   a  and light collectors  92   b  of each set  92 . 
         [0093]    As is shown in  FIG. 8 , the control lever L has a hub  150  and the diffuser  84  together with the screen element  10  and outer diffuser ring  80  bolts onto hub  150  for movement with the hub  150  under the control of the lever L. Thus, the screen element  10  is moved relative to the circuit board  90  (not shown in  FIG. 8 ) which is fixed in a housing of the type shown in the aforementioned International application. 
         [0094]    In alternative embodiments of the invention, rather than providing horizontal bars as shown in  FIG. 1 , the sections may include longitudinal stripes extending in the longitudinal direction of the screen element  10  in each section, which are of generally triangular shape, to thereby provide the varying translucency of the screen element  10 . Still further, rather than providing a V-type output  50  from the section V, the output may be purely linear. Although this embodiment does not provide the advantage of the apex  51  to locate neutral, a reference voltage could still be assigned to neutral and the outputs from the collectors associated with the sections A and B could provide different bands of voltage levels for redundancy purposes and to monitor that the collector associated with the band V is operating properly. 
         [0095]    In this specification it should be understood that the word “light” means electromagnetic radiation of any wavelength and not merely visible light. 
         [0096]    Since modifications within the spirit and scope of the invention may readily be effected by persons skilled within the art, it is to be understood that this invention is not limited to the particular embodiment described by way of example hereinabove. 
         [0097]    In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise”, or variations such as “comprises” or “comprising”, is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.