GB2190995A

GB2190995A - Linear fader

Info

Publication number: GB2190995A
Application number: GB08608588A
Authority: GB
Inventors: Hugh-Peter Granville Kelly
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-04-09
Filing date: 1986-04-09
Publication date: 1987-12-02
Also published as: GB8608588D0

Abstract

A linear fader comprises a slidable control knob 14 which can be operated by hand or under the control of a digitally controlled linear motor 12, 13. An optical transducer arrangement 10, 15 and associated circuitry 18 derive a digital word representative of the position of the control knob which is used both to indicate the setting of the control knob and to achieve servo control of the position of the motor armature. <IMAGE>

Description

SPECIFICATION Digital signal control apparatus The follwing invention relates to apparatus ("faders") used for controlling the amplitude of audio or lighting signals.

Faders are most commonly used in groups in large consoles, such as sound-mixing desks for recording studios, and light controlling desks for theatres and the like. The faders are operated manually and adjust the levels of sound or light as required by the recording or lighting engineers. Typically the construction of these faders comprises a wiper or wipers travelling linearly along a resistive track, rather like an opened out "potentiometer". The faders control the signal amplitude therefore in an analogue manner.

A disadvantage arises from this method of control. Because the control is analogue, each fader can only operate with the particular channel to be controlled. For example, one fader may control the input from only one particular microphone or bank of microphones.

A physical switch, or interconnection must be re-made for the fader to control another alternative input. The ideal solution is where faders and channels controlled by them can be selected at will by an operator, without physical interconnections.

In a first aspect of this invention, a fader, and control circuitry are provided comprising an optical graticule disposed along the length of the fader, and a travelling reading head incorporating one or more optical transducers for reading movement of the head, and circuitry for digitising the outputs from the optical transducers to provide an overall binary word indicating the position of the fader.

Thus, instead of analogue control, the fader's output becomes digital. This can be passed through a digital to analogue connector for normal signal control. However, a significant advantage arises in-as-much that a digital word can be processed or routed to control a host of functions. This control can be effected by a central control computer. Furthermore, the position of any fader at any moment can be recorded digitally, eg on a hard disk, and reproduce at will. A recording engineer can reset the fader to exactly the previously recorded value. This therefore provides great flexibility over analogue systems used hitherto.

Relating now to a second aspect of the invention, automatic faders are now available which comprise the usual analogue fader apparatus as described above but which also incorporate an in-built electric motor. The motor, which is usually of the high-performance D.C. servo type, moves the wipers around using a lead screw and ball race arrangement, or alternatively, a piece of string over pulley wheels. Rotation of the motor, and therefore the position of the wipers, is effected by a closed-loop servo control, using the signal provided by the wipers themselves. These faders can therefore be positioned automatically, by sending to the motor control circuitry an analogue signal representing the desired destination position of the wipers. However, as explained above, these analogue faders can only be used with the channels already assigned to them.Furthermore, they are complicated mechanically, and prone to unreliability.

For example, the string might break, or the lead screw seize. The mechanism interferes with the "feel" of the fader, which is great aesthetic importance to sound-recording engineers.

In a second aspect of the invention, an automatic fader is provided with a linear motor to position the fader head, and specifically, a linear motor as disclosed by my granted patent No. 2079068, which is hereby incorporated by way of reference. Such a linear motor comprises a stator and an armature movable lengthwise relative to one another, the stator and armature each comprising a respective set of magnets disposed in a predetermined sequence in the direction of relative movement, the magnets of one set being arranged in a stack lengthwise of the direction of relative movement and the poles of the other set of magnets being annular and disposed around and slidable relative to the stack, one set of magnets being permanent magnets and the other set being provided by coil windings, the arrangement being such that by appropriate energisation of the coil windings a net thrust to cause relative movement of the armature and stator in a desired direction can be produced at any position in a range of relative armature and stator positions.

Movement of the linear motor is controlled by control circuitry as disclosed by my granted patent No. 2106644 which is also hereby incorporated by way of reference. This method of control includes an optical graticule disposed along the length of the fader, and two optical transducers for reading movement of the motor, which is physically attached to, or comprises part of, the actual head of the fader.

This second aspect of the invention therefore provides in combination the advantage of the first aspect of the invention, namely a digital word indicating the position of the head, and a linear motor for moving the head around under digital control. Thus, these linear motor powered faders can be sent to any digitally defined destination, and when operated manually, (with the motor disenabled), provide a digital word indicating the fader's position. Because the linear motor is the only moving part, there is no need for complicated mechanical components, and the "feel" of the fader can be made virtually identical to conventional faders.

The invention will now be described by way of example with reference to the accompanying drawings in which Fig. 1 shows a view of a linear motor powered fader.

An optical graticule 10 extends along the length of the fader body 11. A linear motor 12 travels along the length of its stator tube 13. Extending from the linear motor is a manual control knob 14. The linear motor also supports an optical transducer assembly 15 housing an infra-red emitter/receiver combination. Depending down from the transducer assembly is a block housing a permanent magnet 16. This traverses along a fixed velocity rod 17. The rod is ferromagnetic and wound with a fine wire. Movement of the magnet induces a current in the wire representing exactly the velocity of the motor. This is used for virtually noiseless closed-loop control.

Operation of the fader is as follows. If the fader is moved manually, the transducer assembly reads this movement from the graticule, and digital circuitry 18 converts the transducer signals into a binary word 19.

(This binary word is then used for controlling the desired signal amplitude). If motor movement is required, a required destination address is sent to the circuitry 18, which process the difference between the current fader position and the required destination, and causes the motor to move thereto as is disclosed in my patent No. 2106644, as mentioned above. At any point, the operator may manually override the motor, simply by holding the knob 14. Detector means on the knob (not shown) senses the presence of a finger of the operator and automatically disenables the motor.

Numerous variations on the above will be apparent to those skilled in the art.

Claims

1. A fader apparatus comprising a fader a user operable control element whose position represents the fader setting, an optical graticule disposed along the length of the fader, a travelling reading head incorporating one or more optical transducers for reading movement of the head, and control circuitry for digitising the output(s) from the optical transducer(s) to provide an overall binary word indicating the position of the control element.

2. A fader apparatus according to claim 1, and adapted for operation in a manual mode in which the setting of the fader is set by the user moving the control element and an automatic mode, the fader apparatus incorporating a linear motor for positioning the control element in the automatic mode.

3. A fader apparatus according to claim 2, wherein the control circuitry is operative in combination with the motor as a position servo for the control element, the desired position being represented as one digital word and the actual position being represented by a second digital word derived from the digitized output(s) of the optical transducers.

4. A fader apparatus according to claim 2 or 3, wherein the linear motor comprises a stator and an armature movable lengthwise relative to one another, the stator and armature each comprising a respective set of magnets disposed in a predetermined sequence in the direction of relative movement, the magnets of one set being arranged in a stack lengthwise of the direction of relative movement and the poles of the other set being annular and disposed around and slidable relative to the stack, one set of magnets being permanent magnets and the other set being provided by coil windings, the arrangement being such that by appropriate energisation of the coil windings a net thrust to cause relative movement of the armature and stator in a desired direction can be produced at any position within a range of relative armature and stator positions.

5. A fader apparatus according to claim 2, 3 or 4 and including a linear velocity transducer extending along the length of the fader, an output signal from the linear velocity transducer representing the speed of the control element being used by the fader control circuitry to achieve substantially noiseless movement of the control element.

6. A fader apparatus according to claim 2, 3, 4 or 5 and including detector means for sensing the presence of the operator's finger and for disabling the motor.

7. A fader apparatus constructed and arranged to operate substantially as hereinbefore described with reference to the accompanying drawings.