Driver unit for an electrically driven vibratory conveyor

Abstract: A drive circuit for an electromechanically excited vibratory conveyor responds to the inductance fluctuations of the conveyor drive coil due to mechanical vibration so as to feed the coil (8) with drive pulses having a repetition frequency commensurate with the natural frequency of the mechanical vibration. Phase and duration of the drive pulses are automatically regulated.

Description: The present invention relates to an electrically driven vibratory conveyor. Vibratory Conveyors comprise a stationary frame, e.g. a base plate, on which springs are mounted. The springs support a conveyor element, say, a cup, a plate or the like. The springs and the conveyor element form a vibratable mass-spring-system which may be electromagnetically driven to oscillate. For this purpose, at least one soft iron yoke carrying at least one coil is mounted on the frame while the conveyor element carries a soft iron armature defining with the yoke an air gap. If the coil or coils are excited with AC current the conveyor element will oscillate in synchronism with the AC frequency, i.e. with 100 oscillations per second on a mains frequency of 50 Hz. The exciting frequency will rarely coincide with the resonant frequency of the mass-spring-system although this would result in the configuration of least energy consumption. Moreover, the resonant frequency of the mechanical system is not constant but depends upon the (additional) mass of the conveyed parts. It is evident that a sensor may be mounted on the mechanical system so as to monitor the actual oscillation frequency and to feed it back to an amplifier which delivers the exciting currents for the coil or coils. Such conveyors are disclosed e.g. in DE-A-41 42 398 and DE-A-36 44 811. Conveyors of the type defined above, however, are not provided with such pickup systems and would have to be modified if the user wanted to operate them in the resonant, mode. US-A-4 663 574 discloses a vibratory feeder operating near the resonant frequency in which the amplitude of the vibration is calculated from the current and voltage of the driving unit. It is therefore an object of the present invention to provide a driver unit for electromagnetically vibratable conveyors to be driven at least close to the resonant mode and wherein no modifications of the mechanical system need be provided. The above underlying problems are solved according to claim 1. In accordance with the present invention, fluctuations of the inductance of the electromagnetic drive means, caused by the air gap variations due to the mechanical oscillations, are processed. Preferably, the coil is connected into an electrical oscillator circuit so as to determine the resonant frequency of the latter. This circuit forms together with amplifier circuits an electrical oscillator. The oscillations of the latter are frequency modulated with the frequency of the mechanical vibrations because the inductor varies periodically in synchronism with the mechanical vibrations. Preferably, the duration of the period of those vibrations is processed. The fluctuations of the latter, i.e. the modulation "depth" will be the higher the greater the vibration amplitude of the mechanical oscillation will be so that not only the phase position but also the intensity of the drive pulses may be controlled, preferably automatically regulated using a servo loop. An embodiment of the invention is illustrated in the attached drawings and will be explained in detail hereunder with reference thereto. Fig. 1 illustrates schematically a side elevation of a conventional vibratory conveyor. Fig. 2 illustrates the circuit diagram of the driver unit in accordance with the invention. Referring first to Fig. 1, a conveyor element which in the example is a conveyor plate 2 supported on springs 3 excited to vibrate in a direction indicated by arrow 4 so as to convey objects 1 in a direction indicated by the arrow of object 1. The springs are mounted on a base plate 5 which moreover carries a soft iron yoke 6. The yoke defines, together with an armature 7 mounted on conveyor plate 2, an air gap. A coil 8 is disposed on yoke 6, the coil being driven with driver pulses so as to excite mechanical vibrations of the spring-plate-objects-system. The repetition frequency of the driver pulses should at least approximate the natural frequency of the vibratable mechanical system. The mechanical vibration amplitude may be affected by the amplitude and/or the duration (width) of the drive pulses. The natural frequency of available conveyors is usually in a range of from about 30 Hz to 150 Hz. The inductance of the exciting system comprised of yoke, coil, and armature fluctuates in synchronism with the vibrations because the air gap varies periodically. In accordance with the present invention, those inductance fluctuations are utilized to generate a control signal for the drive unit. Referring now to Fig. 2, coil 8 is grounded with one of its ends while its other end is connected, via a switching transistor 9, to a DC voltage carrying conductor. The DC voltage may be full-wave rectified and smoothed mains voltage. Coil 8 forms together with two pairs of capacitors 10, 11 an electric resonant circuit having its own natural frequency which, in use of the conveyor, varies in synchronism with the vibrations of the latter; the circuit resonant frequency will generally be in the order of some ten KHz. The resonant circuit is excited by means of the two amplifiers 12 and 13. Two transistors 22 and 23 are disposed in a feedback path of amplifier 12, the transistors serving the purpose to balance the high voltage transients across coil 8 in that the output of amplifier 12 is coupled via resistor 25 to their base terminals. In result, the working point at the amplifier input returns rapidly to its normal position within the intervals between the drive pulses. The square voltage at the output of amplifier 13 is converted into needle pulses by means of inverter 14 and EXOR gate 15. The temporal spacings between successive needle pulses are equal to the period of the actual oscillation frequency of the resonant LC circuit. A counter 16 is incremented at its counting input with a fixed frequency of e.g. 16 MHz, and the actual count is fed to a central processing unit, e.g. a normal microprocessor. The needle pulse from gate 15 signals to the central processing unit to process the actual count, and the same needle pulse resets the counter to zero. The count thus fluctuates in synchronism with the mechanical vibrations of the conveyor so that the central processing unit may derive therefrom the actual position of the conveyor element and may calculate the most efficient instant for the drive pulse. Moreover, the difference between maximum count and minimum count represents the vibration amplitude of the conveyor, amplitude which may be adjusted or automatically regulated by a corresponding selection of the drive pulse duration. The drive pulses are triggered by the central processing unit 17 via an opto-coupler 18 at the input of switching transistor 9. The voltage peaks across the coil 8 caused by the energy stored in the windings are discharged via diodes 26, 27. The actual value of the drive pulse is fed back to the central processing unit by means of resistors 19, 20, 21. An adjustment panel 28 is connected to the central processing unit and permits to the user to set target values for the vibration amplitude of the conveyor and the phase position of the drive pulses. If a quiescent DC current is flowing in the coil AC voltages will be induced therein in synchronism with the conveyor vibrations which may be processed to generate the drive pulses under the provision that the DC current is sufficiently high to result in a convenient signal-to-noise-ratio.

Claims: A drive unit for an electromagnetically excited vibratory conveyor, the conveyor including a drive coil having an inductance periodically supplied with drive pulses generated by said drive unit, said drive unit comprising a circuit wherein fluctuation of said inductance due to mechanical vibration are processed to define at least temporal instants of drive pulse supply. The drive unit of claim 1 wherein said coil forms part of an oscillator circuit oscillating with an oscillator frequency, said oscillator frequency fluctuating in synchronism with said mechanical vibrations. The drive unit of claim 2 adapted to process a period duration of said fluctuations. The drive unit of claim 1 or 2 adapted to define an amplitude of said drive pulses. The drive unit of claim 1 or 2 adapted to define a duration of said drive pulses. The drive unit of claim 3 wherein a difference between a maximum period duration and a minimum period duration is processed as a representation of amplitudes of said mechanical vibrations. The drive unit of claim 2 including active components for stabilizing a working point of said oscillator. The drive unit of claim 1 or claim 2 including servo means for said temporal instants. The drive unit of claim 1 or claim 2 including servo means for a drive pulse duration. The drive unit of claim 1 including means for feeding said coil with a bias DC current and means to process voltage induced in said coil when said conveyor is vibrating. A vibratory conveyor, comprising: a stationary base, spring elements mounted on said base, a conveyor element supported by said spring elements and forming therewith a vibratable system, a soft iron yoke, a coil disposed on said yoke, an armature defining with said yoke an air gap, one of said yoke and armature being mounted on said base and the other of said yoke and armature being mounted on said conveyor element, and a drive unit as defined in claim 1.

Inventors: MEITINGER THOMAS DIPL-ING, MEITINGER, THOMAS, DIPL.-ING.
Applicants: MEITINGER THOMAS DIPL ING, MRW DIGIT ELECTRONICGERAETE GM, MEITINGER, THOMAS, DIPL.-ING., MRW DIGIT ELECTRONICGERAETE GMBH
Application year: 1996
Main classification: G05D19
IPC codes: G05D19, B65G27