APPARATUS FOR PRODUCING CONTROLLED MOVEMENT

Abstract: A motorised fader for audio or lighting controls includes a manually adjustable slider (10; 36), a linear magnetic motor with an elongate electromagnetic coil (20; 39, 40) extending over the length of movement of the slider, and a powerful permanent magnet (14; 38) secured to the slider and with its magnetic axis perpendicular to the magnetic axis of the coil. The slider (36) may have a manual control knob (44) which is electrically connected to a control circuit (Figure 5) by a switching means (86 to 90), so that upon touching the knob (44) d.c. current to the coil is cut off to enable the slider to be freely moved.

Description: Title: Apparatus for producing controlled movement Field of the invention This invention relates to apparatus for producing controlled movement of a device along a path, and is more particularly but not exclusively concerned with otorised faders for use in studios for controlling audio or video signals and/or lighting. Background to the invention In ' many applications it is necessary to move a device to a particular position or sequence of positions. For example, in studios it may be necessary to move one or more sliders for lighting or audio equipment to predetermined positions. This has heretofore been done by using known motorised faders having d.c electric motors, requiring gearboxes, moving belts and ancillary driving equipment. Summary of the invention According to one aspect of the present invention there is provided a motorised fader for use in adjusting the setting of sound or lighting, which latter includes a slider, means for manual adjustment of the position of the slider, and a linear magnetic motor comprising an elongate electromagnet extending over at least the length of the path of movement of the slider and a permanent magnet secured to the slider with its magnetic axis substantially perpendicular to the magnetic axis of the electromagnet. Since there is no mechanical or electrical coupling between the slider and the motor, the resistance to movement of the slider can be of a very low order so that smooth and easy manual adjustment of the slider position is possible. Moreover since there are no mechanical parts such as pulleys or gearboxes in the motor, the reliability and life of the device are substantially improved. According to another aspect of the invention there is provided a motorised fader for producing controlled movement of a slidable member along a path, comprising a manual control for manually positioning the slidable member along the path, a fixed electromagnetic coil extending at least the length of the path, circuit means for supplying d.c current to the coil, at least one permanent magnet secured to the slidable member and mounted with its magnetic axis substantially perpendicular to the magnetic axis of the coil and to the direction of movement and with one pole close to the coil, and switch means associated with the manual control and connected in the circuit means so that during manual movement of the slidable member electric current is reduced or cut off to enable the slidable member to move freely. The switch means may be touch sensitive. Preferably a position transducer means is associated with the slidable member to produce an electrical signal having a parameter which varies in a known manner depending on the position of the slidable member along the path. In this way the direction of flow of the current supplied to the coil can be controlled to provide the desired direction of movement, and the magnitude of the current may be controlled to give the desired acceleration and velocity of the slidable member. The position transducer preferably includes a resistive position track disposed along the path and adapted to feed a signal to the circuit means corresponding to the position of the slidable member. The path of movement is typically linear. Advantageously a second coil is disposed with its magnetic axis parallel to that of the first coil, with the spacing between the coils such that each is close to the path of one of the poles of the magnet. The permanent magnet is preferably a rare earth magnet, having a high coercive force . A preferred material for the magnet is Neodynium Iron Boron. An alternative magnetic material is Samarium Cobalt. The invention is of primary application to drive manually adjustable controls in consoles for controlling audio and lighting on stage or in studios or auditoriums. However, other analagous applications are possible, such as in robotics, telemetry, remote control and steering systems, and generally in any powered adjuster which includes and provides for manual override. By utilising a linear magnetic motor greater potential accuracy is obtained compared with prior art system, in which movement is imparted in incremental steps from a rotary drive such as a d.c motor. Brief description of the drawings The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic diagram of a drive unit for a fader, constructed as one embodiment of the invention; Figure 2 is perspective view of a drive unit for driving a fader, constructed as a second embodiment of the invention; Figure 3 is a side view, partly in section, of the drive unit of Figure 2; Figure 4 is a section taken through the line IV - IV of Figure 3 and including the fader; and Figure 5 is a circuit diagram of the control circuit for the motorised fader drive unit of Figures 2 to 4. Specific description In Figure 1 a slidable member 10 is slidable along a track 12 and includes a permanent magnet 14 and a sliding contact 16 of a linear potentiometer 18. Positioned in close proximity to the permanent magnet 14 and disposed parallel to the track 12 is an electromagnetic coil 20 wound on a magnetisable core 22. The ends of the coil 20 are electrically connected to a control unit 24 which incorporates a memory and is capable of delivering sufficient d.c electric current to the coil to cause the member 10 to move along the track 12. The magnitude and direction of such driving current are controlled by the input data at 26, which may be in analogue or digital form. Amongst such input data is a feed back control signal which, is derived from the slider 16 and which is supplied to the control unit 24 via a signal path 30. It will be understood that more than one coil such as 20 may be employed. Furthermore two or more cores 22 may be employed, and these may be in the form of tubes or discs. The track 12 may be an integral part of the magnetic assembly. The apparatus is capable of adaptation to any system which requires a device to be moved to a predetermined position along a track, or which requires a member to be moved at a desired velocity or acceleration, but which must allow for manual override. Where the unit 24 has a memory, this may store a plurality of different settings or programmed movements previously performed by the manual override, allowing a sequence of movements to be repeated when required. Figures 2 to 4 show a drive unit for a fader which can be linked to a movable element of the fader and be mounted side by side with other similar drives to control a number of parallel arranged faders in a console, for use (for example) in a recording studio, theatre or the like. An exterior casing 30 and end mouldings 32 support a pair of slide rails 34 mounted parallel one above the other. The rails 34 are made of non-magnetic material, and slidable therealong is a carriage 36 for a powerful permanent magnet 38. The magnet is made of a rare earth composition, such as of Neodyniu Iron Boron or Samarium Cobalt, and has its N-S axis disposed transverse to the axis of the rails 34, as shown in Figure 4. A pair of coils 39, 40 wound on cores 42, 43 respectively are located on opposite sides of the magnet 38. The cores 42, 43 are of rectangular section and formed from iron or other high reluctance material. The wire of each winding is typically 0.15 mm in diameter and the coil is close-wound in eight layers. A control knob 44 extends from the carriage 36 to enable the latter to be moved manually along the rails 34. Disposed opposite the upper rail 34 is a linear resistance track 52 having a total electrical resistance of 10 K ohms. The movable carriage 36 carries a pair of electrical wipers 54 which make contact with the track 52. The resistance measured from one end of the track 52 to the wipers 54 gives a position reference signal. The windings 40 are arranged in parallel and connected to a 30 yolt d.c supply in such a manner that the direction of the magnetic field produced in one coil is opposite to that of the other coil. When a current flows through the windings, the interaction between the magnetic field produced by the currents and that of the permanent magnet 38 results in a distortion of the magnetic field which produces a net force on the carriage in a direction which will cause the latter to slide along the rail 34. Typically a force of about 2 Newtons has been observed, using a magnet of 30 megaGauss Oersteds. An arm 56 extends below the carriage 36 to transmit motion to a movable control element 57 of a fader 59 (see Figure 4). Figure 5 is a control circuit for the drive unit of Figures 2 to 4. The upper half of the circuit diagram is a servo control circuit, while the lower half provides an electrical signal if the knob 44 is touched by hand (and therefore either becomes earthed or has ambient radiated mains hum applied to it by the hand), and acts to interrupt the flow of current from the power supply to the motor in response to the electrical signal. The servo control is supplied with a voltage from the wipers 54 which is buffered by an operational amplifier 60 to provide one input to a comparator 62, the other input of which is supplied from a virtual earth summing amplifier 64 the gain of which is adjustable by a feedback resistor 66 to set the amount of damping. The output from amplifier 60, shown as "SERVO OUT", feeds the data acquisition input of an external control unit (similar to the control unit 24 of Figure 1), while the input to amplifier 68, shown as "CONTROL IN", provides the feed to the motor from.the external control unit. Two back-to-back diodes 70, 72 adjust the size of the hysteresis of the comparator 62 to prevent oscillation around any desired position of the carriage 36. The output stage is driven by a phase splitter 74, 76 and comprises four power transistors 78, 80, 82, 84 arranged in a bridge circuit to control the current to the motor (not shown) . The value of the current is determined by the distance between the desired position of the carriage 36 and the actual position indicated by the track 52, the velocity of approach to the desired position also being taken into account. In accordance with the invention, as soon as the knob 44 is touched by hand the current to the motor is reduced or cut off, allowing free movement of the control knob, so that the only resistance to movement is the friction associated with the slide rails 34. This is achieved by CMOS devices 86, 88, 90 connected in cascade and having a very high input impedance. The input to device 86 is connected via a 100 Kohm resistor 92 to the manual control knob 44, which itself is of electrically conducting material. If the knob 44 is touched by a finger or thumb, the surface conductivity of the skin is sufficient either to create earth leakage or to inject an ambient mains hum to the device 86 either of which conditions causes a triggering of device 86 and hence of device 88, which produces a rise in the voltage across resistor 94 and causes device 90 to fully conduct and the output terminal 96 to shift from +5V to -0.7V. This turns off drive 98 in the input of device 76 in the phase splitting/driver stage 74, 76 and immediately results in the power transistors 78 to 84 being turned off and in turn removing the driving current from the motor.

Claims: Claims 1. A motorised fader for use in driving a manually adjustable control for audio or lighting, comprising a slider, adjustment means for manual adjustment of the position of the slider, and a linear magnetic motor including an elongate electromagnet extending over at least the length of the path of movement of the slider and a permanent magnet secured to the slider with its magnetic axis substantially perpendicular to the magnetic axis of the electromagnet. 2. A fader according to claim 1 further comprising circuit means for supplying d.c. current to the electromagnet and switch means associated with the adjustment means and connected in the circuit means so that during manual movement of the slider the d.c. current to the electromagnet is reduced or cut off to enable the slider to move freely. 3. A fader according to claim 2 in which the switch means is touch sensitive. 4. A fader according to claim 2 or claim 3 in which a position transducer is associated with the slider to produce in the circuit means an electrical signal having a parameter which varies in a known manner depending on the position of the slider along the path. 5. A fader according to claim 4 in which the position transducer includes a resistive position track disposed along the path and adapted to feed a signal to the circuit means corresponding to the position of the slider. 6. A fader according to any one preceding claim in which said path of movement is linear. T. A fader according to any one preceding claim further comprising a second electromagnet disposed with its magnetic axis parallel to that of the first electromagnet, with the spacing therebetween being such that each electromagnet is close to the path of one of the poles of the permanent magnet. 8. A fader according to any one preceding claim in which the permanent magnet is a rare earth magnet, having a high coercive force. 9. A fader according to claim 8 in which the material for the permanent magnet is Neodynium Iron Boron. 10. A fader according to claim 8 in which the material ' for the permanent magnet is Samarium Cobolt .

Inventors: WHITTAKER ROBIN, WYGNANSKI WLADYSLAW, WHITTAKER, ROBIN, WYGNANSKI, WLADYSLAW
Applicants: OUT BOARD ELECTRONICS LTD
Application year: 1988
Main classification: H04H7
IPC codes: G05B1, G05D3, H01C10, H02K41, H02P25, H04H60