Abstract:
A compact low profile fader has an elongate support and a manually settable slider mounted for linearly slidable relative to the elongate support. A drive transmission operably interconnecting the slider and a digital encoder so that movement of the slider produces a digital output signal from the digital encoder. The digital encoder has a rotatable encoder disk and is mounted so that its longitudinal direction of extent is in alignment with that of the elongate support. The drive transmission includes a drive pulley and a loop of cord which is wound around the pulley. The pulley drives the rotatable encoder and has a helical groove in its peripheral surface. The cord is engaged in the helical groove and with the slider so that movement of the latter causes the pulley, and thereby the rotatable encoder disk, to be rotated.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is the national phase of International (PCT) Patent Application Serial No. PCT/GB02/00929, filed Mar. 4, 2002, published under PCT Article 21(2) in English, which claims priority to and the benefit of British Patent Application No. 0105196.0, filed Mar. 2, 2001, the disclosure of each of which is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   This invention relates to a signal controller for providing an output signal which is dependent upon the position of a manually settable element, more particularly the present invention is concerned with a linear motion fader having a compact low profile for mounting in a control desk. 
   Most current linear motion faders for recording studio mixing desks are analogue potential dividers with a ‘tap off’ voltage determined by the position of a manually settable slider and controlling the volume level or amplitude associated with a given channel. 
   A disadvantage associated with such analogue faders is that, as sound processing moves away from analogue and towards digital processing, the analogue output from existing faders must be converted to a digital signal, thus introducing a further processing step. 
   WO 97/13121 (and corresponding U.S. Pat. No. 5,719,570 and U.S. Pat. No. 5,986,584) discloses an optical encoder-based fader in which an elongate frame member carries a manually operable linear slider which is slidable longitudinally of the frame member. A taut string or wire is wrapped around pulleys at opposite ends of the frame member and is also connected to the slider so that linear movement of the sliders causes the pulleys to rotate. The pulleys are mounted with their axes of rotation perpendicular to the direction of sliding movement of the slider. One of the pulleys is mounted on the shaft of a rotary optical encoder, whilst the other pulley is mounted on the shaft of a motor which can be used to move the string when it is desired to “replay” a previous editing or mixing sequence. Such an arrangement is not particularly compact in the depthwise direction, particularly at both ends of the fader. Also, simply wrapping the string around the pulleys does not ensure that there a good control over the output of the encoder or a smooth feel to the slider. 
   As control desk manufacturers make their units smaller and lower, it becomes increasingly difficult to use motorised faders within the required space envelope. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a potentially compact form of signal controller which mitigates the above disadvantage. 
   According to the present invention, there is provided a signal controller including an elongate support, a manually settable slider mounted for linear reciprocatory sliding movement between limit positions relative to the elongate support, a digital encoder having a rotary encoder member, and a drive transmission including a loop of filamentary material operably interconnecting the slider and the rotary encoder member such that, in use, movement of the slider produces a digital output signal from the digital encoder, wherein the digital encoder has a longitudinal direction of extent which is in substantial alignment with that of the elongate support. 
   Conveniently, the rotary encoder member has an axis of rotation which extends in the longitudinal direction of extent of the digital encoder. 
   The drive transmission preferably includes a pair of first pulleys at or adjacent a first end of the elongate support and a pair of second pulleys at or adjacent a second, opposite, end of the elongate support, the pulleys of each pair being mutually spaced apart laterally relative to the longitudinal direction of extent of the elongate support, wherein the filamentary material passes around the first and second pulleys. 
   Preferably, the drive transmission includes a rotary transmission element which is operably connected to the rotary encoder member and around which the loop of filamentary material passes. 
   The rotary transmission element preferably has an axis of rotation which extends in the longitudinal direction of extent of the elongate support. 
   Preferably, the rotary transmission member has a slot therein in which the filamentary material is received. The slot can serve to prevent slip of the filamentary material relative to the rotary transmission member in use. The slot is preferably disposed in an end surface of the rotary transmission member so as to extend transversely with respect to the axis of rotation of the latter. Conveniently, the slot extends chordally so as to open at each end onto the peripheral surface of the rotary transmission member. 
   Preferably, the loop of filamentary material has a knot therein which joins opposite ends of a length of the filamentary material to form the loop, and the knot is disposed within the slot, preferably within an enlarged region of the slot 
   More preferably, the rotary transmission element is disposed adjacent said first end of the support and between the first pulleys but is displaced below the axis of movement of the slider, and the filamentary material passes over one of the first pulleys, several times (preferably at least 2.5 times to ensure no slippage) around the rotary transmission element and then back over the other of the first pulleys. 
   The terms “upper”, “lower” and “below” as used herein refer to the positions of the respective parts when the signal controller is mounted in a horizontal or slightly inclined control panel. 
   Preferably, the first pulleys have their axes of rotation mutually inclined such that the axis of rotation of each first pulley is approximately perpendicular to the direction of extent of a region of the filamentary material which extends between that first pulley and the rotary transmission element. This reduces wear of the filamentary material during passage over the first pulleys. 
   Preferably, the first pulleys are mounted so that they are mutually displaced in the longitudinal direction of the elongate support by a distance which corresponds approximately to the separation, along the longitudinal axis of the rotary transmission element, between those regions of the filamentary material which extend from the transmission element to the respective first pulleys. 
   Most conveniently, the rotatable encoder member has its axis of rotation coincident with that of the rotary transmission element. 
   The signal controller preferably further includes a motor which is drivingly connected with the rotary transmission element and the rotatable encoder member. The position of the slider can be altered between studio sessions and it is often important to reproduce exactly the same settings over a bank of faders from one session to the next. In order to achieve this, the positions of the sliders are stored electronically at the end of a session, and the motors are generally used to drive the sliders to the desired position at the start of a session. 
   In order to provide a particularly compact low profile arrangement, it is preferred for the motor to be displaced below the axis of movement of the slider and mounted with its longitudinal direction of extent in substantial alignment with that of the elongate support. 
   Most conveniently, there is a direct drive between the motor and the rotary transmission element and the rotatable encoder member. The rotary transmission element may be fitted on the side of the rotatable encoder member remote from the motor, but is preferably mounted between the motor and the rotatable encoder member. 
   The digital encoder may be an optical encoder wherein the rotatable encoder member is a toothed or apertured disk, or it may be a magnetic encoder including a magneto-resistive or a Hall-effect device wherein the rotatable encoder member has magnetic regions thereon. The encoder may be quadrature sensitive in order to distinguish the direction of movement of the position indicator. 
   Preferably, the rotary transmission element has a cylindrical surface with a helical groove therein, and the loop of filamentary material is wound around the cylindrical surface so as to engage in the helical groove. 
   The filamentary material may be a cord, wire, string, cable or other filamentary material of approximately circular cross-section. This facilitates implementation of the arrangement with the encoder in substantial alignment with that of the elongate support. This is because, in such an arrangement, there are three-dimensional changes in the path of movement of the filamentary material, as compared to the use of a toothed drive band. Also, the use of a toothed drive band can result in a rough feel to the slider because of the engagement of the teeth in the belt with a toothed transmission element driven by the belt. The use of a filamentary material which is wound in a helical groove in the rotary transmission element gives a smoother feel to the slider. The helical groove serves to control the position of the turns of the filamentary material on the rotary transmission element so that there is little likelihood of the turns overlapping one another during rotation of the element 
   Preferably the slider is touch sensitive to facilitate discrimination between manual operation and motor operation of the slider. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example, with reference to the accompanying drawings in which: 
       FIG. 1  is a perspective view of a signal controller according to the present invention in the form of a linear motion digital fader shown without a cover thereon; 
       FIG. 2  is a view of a first end of the fader of  FIG. 1 ; 
       FIG. 3  is a plan view of part of the fader of  FIGS. 1 and 2  showing the arrangement of pulleys at the first end of the fader: 
       FIG. 4  is a perspective view of a cover for the fader of  FIGS. 1  to  3 ; 
       FIG. 5  is a perspective view of parts of the fader of  FIGS. 1  to  4 ; 
       FIG. 6  is a perspective view showing a slider of the fader in greater detail; 
       FIG. 7  is a perspective view showing the mounting of a motor of the fader in greater detail; 
       FIG. 8  is an exploded perspective view showing a slider mounting tube of the fader in greater detail; and 
       FIG. 9  is a detail view showing a preferred embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The linear motion digital fader as illustrated in the drawings basically comprises an elongate support  10 , a manually settable slider  12 , a digital encoder  14 , a drive transmission  16  including a continuous loop of cord  18 , and an electric motor  20 . 
   The elongate support  10  is moulded from a plastics material such as an acetal resin and includes a base  10   a , a side wall  10   b  extending upwardly from one longitudinal side of the base  10   a , an end wall  10   c  at a first end of the body  10 , and an apertured flange  10   d . The end wall  10   c  has an aperture therein which is substantially aligned with that in the flange  10   d . Both the end wall  10   c  and the apertured flange  10   d  extend away from, the base  10   a  on the opposite surface thereof to the side wall  10   b . The elongate support  10  is formed with first and second mouldings  10   e  and  10   f  at its first end and its opposite, second end, respectively. The mouldings  10   e  and  10   f  have holes  22  and  24  therein which, in use, receive fixing screws (not shown) for attaching the fader together with an attached casing  26  (see  FIG. 4 ) under the panel of a control desk (not shown). The first moulding  10   e  has a pair of further holes  28  therein (see particularly  FIGS. 1 ,  3  and  8 ). The first moulding  10   e  is formed with a mounting boss  32  ( FIG. 8 ) which faces in the direction of the second end of the support  10 . 
   At the second end of the elongate support  10 , there are a pair of bushes  30  which are integrally moulded with the support  10  (see particularly FIG.  8 ). The second moulding  10   f  includes a C-shaped recess  34  which is directed towards the first end of the support  10  and which opens upwardly. The mounting boss  32  and the recess  34  are mutually aligned and receive opposite ends of a tube  36 . The boss  32  fits into one end of the tube  36  whilst the opposite end of the tube is snap-fitted into the recess  34  via its upper opening. In this way, the tube  36  is firmly held in position so that it extends longitudinally of the elongate support  10  parallel to the side wall  10   b.    
   The slider  12  (see particularly  FIG. 6 ) comprises a pair of bushes  38  through which the tube  36  passes. Thus, the tube  36  is passed through the bushes  38  before being secured in the elongate support  10 . The bushes  38  are disposed to one side of an upstanding T-shaped flange  40  of the slider  12 . On the opposite side of the T-shaped flange  40 , the slider  12  is provided with an integrally moulded shaped tang  42  which is shaped so that a first portion  42   a  thereof engages against the upper edge of the side wall  10   b , whilst a second portion  42   b  thereof engages in a groove  44  in the inner surface of the side wall  10   b . The groove  44  extends longitudinally of the elongate support  10 . It will therefore be understood that the provision of the bushes  38  which slide on the tube  36  and the tang  42  which engages against the top of the side wall  10   b  and in the groove  44  therein provides a good bearing surface for sliding movement of the slider  12  and also minimises wobble of the slider  12  in use. 
   The digital encoder  14  includes a rotatable encoder disk  46  with a multiplicity of radial slits therethrough around its circumference. The disk  46  is secured to the end of a rotary shaft  48 . The disk  46  extends into a slot  50  in a housing  52  in which a LED and one or more photodiodes or phototransistors (not shown) are mounted in alignment with the path of movement of the slits in the disk  46 . The LED is disposed on opposite side of the disk  46  to the photodiode(s)/phototransistor(s). The housing  52  is mounted on a rectangular printed circuit board  54  which is disposed below the axis of sliding movement of the slider  12 . The printed circuit board  54  is secured to the bottom edges of the end wall  10   c  and the apertured flange  10   d  by means of deformable mounting posts  58  (see FIG.  7 ). The printed circuit board  54  also carries an electrical connector  58  to enable the required electrical connections to be made to the fader. 
   The motor  20  has axial mounting bosses  56  (only one shown—see  FIG. 7 ) at opposite ends thereof. One of the mounting bosses  56  (illustrated in  FIG. 7 ) is engaged in the aperture in the end wall  10   c  whilst the other mounting boss is engaged in the aperture in the flange  10   d . The flange  10   d  is sufficiently flexible that the motor  20  can be engaged first with the end wall  10   c  and then snap-fitted into engagement with the apertured flange  10   d . In this way, the motor  20  is firmly held in position under the base  10   a.    
   The shaft  48  is in alignment with, and secured to a rotor shaft (not shown), of the motor  20 . Thus, the shaft  48  is drivable directly by the motor  20  about an axis which extends longitudinally relative to the elongate support  10  and below the slider  12 . 
   The drive transmission  16  includes a cylindrical transmission pulley  60  which is mounted on the shaft  48  between the disk  4 &amp; and the motor  20 . The pulley  60  has a cylindrical peripheral surface in which a scroll or helical groove  60   a  ( FIG. 9 ) is provided. The pitch of the helical groove  60   a  is slightly larger than the diameter of the cord  18 . Parts of the cord  18  are wound several times (in this embodiment about 5 times) around the pulley  50  so as to lie in the groove. In a preferred embodiment (see FIG.  9 ), the ends of the cord  18  are joined together by a knot  18   a  to form the continuous loop are engaged, along with the knot  18   a , in a transverse chordal slot  51  formed in the end of the pulley  50 . The knot  18   a  is engaged in an enlarged region  51   a  centrally of the slot  51 . The slot  51  opens at each end onto the peripheral surface of the pulley  50  to allow the cord  18  to be engaged in the helical groove. The portions of the cord  18  on either side of the slot  51  are wound around the groove  60   a  2.5 times in order to obtain the number of revolutions of the pulley  60  that equates to the linear stroke of the fader. The location of the cord  18  and knot  18   a  in the slot  51  serves to retain the cord  18  securely in place without risk of slipping relative to the pulley  50  in use, and avoids an arrangement where the knot  18   a  has to pass over any of the pulleys. 
   As can be seen from  FIG. 1 , the transmission pulley  60  is disposed adjacent to the outer surface of the end wall  10   c  and below the moulding  10   e  at the first end of the elongate support  10   
   Portions of the cord  18  extend upwardly from opposite sides of the transmission pulley  60  and each passes around a respective one of pair of first pulleys  62  and  64 . From the first pulley  62 ; the cord  18  runs along the elongate support  10  to the opposite, second end where it passes around a pair of second pulleys  66  and  68 . From the pulley  68 , the cord  18  passes back to the first pulley  64 . However, between the second pulley  68  and the first pulley  64 , the cord  18  is clamped to the tang  42  of the slider  12 . 
   The second pulleys  66  and  68  are rotatable about vertical axes and are mounted on the bushes  30  at the second end of the elongate support  10 . The first pulleys  62  and  64  are mounted in the holes  28  in the first moulding  10   e  so that each of their axes of rotation is approximately perpendicular to the direction of extent of the portion of the cord  18  which runs between the transmission pulley  60  and the respective first pulley  62  and  64 . This can be seen in FIG.  2 . Such arrangement reduces wear on the cord  18  against the sides flanges of the first pulleys  62  and  64 . Additionally, and as can be seen in  FIG. 3 , the first pulleys  62  and  64  are mounted in the first moulding  10   e  so that they are mutually displaced in the longitudinal direction of the elongate support  10 . The mutual displacement corresponds approximately to the separation, along the longitudinal axis of the transmission pulley  60 , between those portions of the cord  18  which extend from the transmission pulley  60  to the respective first pulleys  62  and  64 . This axial displacement is as a result of the wrapping of the cord  18  a number of times around the transmission pulley  60 . The arrangement is such that, when the slider  12  is approximately in the mid-position of its sliding movement, the cord  18  engages each first pulley  62  and  64  over an angle of 90 degrees. 
   Referring now to  FIG. 4 , the casing  26  has a slot  70  therein through which the T-shaped flange  40  of the slider  12  passes with clearance. The casing  26  is held in position by deformable fixing tabs  76  and guide tabs  78  which engage variously with the elongate support  10  and the printed circuit board  54 . The casing  26  also has integral support legs that enable the fader to be soldered into a printed circuit board directly below the fader. 
   The T-shaped flange  40  of the slider  12  is fitted with a touch-sensitive, conductive knob (not shown) which is connected by a flexible cable (also not shown) to the printed circuit board  54 . 
   The motor  20  is used to drive the slider  12 , via the transmission pulley  60  and the cord  18 , to its desired position, from a known reference position, during an initial set-up operation. The rotation of the transmission pulley  60  is also transmitted to the encoder disk  46 . 
   Upon touching the control knob on the slider  12 , an operator automatically disengages the motor  20 , in a manner known per se so that the slider  12  becomes manually operable. The manual operation of the slider  12  is translated by the cord  18  into rotation of the encoder disk  46 . 
   As the slits of the encoder disk  46  pass in front of the LED, the light passing through the slits is sensed in a quadrature sensitive manner by the photodiode(s)/phototransistor)(s) of the digital encoder  14 . The quadrature sensitive manner of the light detection allows the direction of motion of the slider  12  to be determined. The digital output from the digital encoder  14  can be either sine-wave quadrature form or Schmidt triggered. The sine-wave quadrature output gives a high-resolution output signal, whereas the Schmidt triggered output allows the use of low cost digital interfacing circuitry. 
   The position of the slider  12  relative to a reference position can be calculated from the number of pulses output from the photodiode(s)/phototransistor(s) and subsequent processing converts this into the signal associated with the given channel. 
   The arrangement of the components within the fader is a very compact and efficient arrangement, thereby increasing the response speed of operation of the slider  12  when driven by the motor  20 . Also, the resolution of motion sensing is enhanced as a result of the relatively large diameter ratio of the encoder disk  46  to the transmission pulley  60 .