WO1986002058A1

WO1986002058A1 - Device for controlling of magnetically driven mass oscillating systems

Info

Publication number: WO1986002058A1
Application number: PCT/EP1985/000479
Authority: WO
Inventors: Bruno Pross; Arthur Kobler
Original assignee: Bruno Pross; Arthur Kobler
Priority date: 1984-10-05
Filing date: 1985-09-17
Publication date: 1986-04-10
Also published as: AU4868285A; CH666359A5; EP0197136A1

Abstract

The device, which for example can be applied to conveyor of bulk materials, small pieces or the like, comprises: a first means: consisting of a device (5, 10), which can measure the resonance frequency, the phase and the oscillation amplitude of the mass oscillating system; a second means: consisting of a control device, which independently adjusts the excitation frequency to the natural frequency of the mass oscillating system and feeds the excitation energy at the optimal time and in the necessary amount to the magnetic drive (5, 4) to bring the system to the desired oscillation amplitude with minimal energy. Consequently, as a rule resonance adjustment of the mass oscillating system can be dispensed with from now on, since the device independently adjusts to the resonance with an excitation frequency.

Description

Device for controlling of magnetically driven mass oscilla- tin systems.

The invention relates to a device for controlling of magne¬ tically driven mass oscillating systems, such as conveyours or the like, in which the resonance frequencies are diffe¬ rent and moreover can vary in any way during operation.

So-called magnetic oscillating conveyors are very often used in industry for moving of bulk materials or small pie¬ ces. These devices consist of a conveyor part, which is designed as a conveyor trough, conveyor pipe or conveyor chute, in addition to a countermass (stator). The conveyor part and the countermass are connected with one another by spring elements. These devices are designated in the litera¬ ture by the full name of so-called magnetically driven 2-mass oscillating systems.

If the spring elements in each case are mounted at an angle opposite a stationary base, i.e., opposite the contermass, and the 2-mass system oscillates with the aid of an electro¬ magnet, i.e., a magnet armature and magnet coil, then the pieces on the conveyor chute that are to be conveyed begin to move in a fixed direction, corresponding to a so-called projectile motion.

Since known mechanical designs, especially mechanical oscil- lating systems, are prone to considerable oscillations only close to their resonance frequency, their resonance frequen¬ cy must be adjusted close to the driving frequency of the magnetic drive. Particularly since 50 Hz or 60 Hz are avai¬ lable from the power supply system an excitation frequency of 100 Hz or 120 Hz is necessarily produced if the electro¬ magnet is connected directly. With diode rectifiers, thyri- stors, etc being connected, 50 Hz optionally 25 Hz or 60 Hz and optionally 30 Hz is produced.

The natural frequency of a 2-mass oscillating system is calculated from

(Hz) (formula l)

Useful weight x stator weight

Total of Weights = (formula 2)

Useful weight x stator weight

Useful weight = table weight + conveyor attachment + the weight of the partly coupled material to be conveyed. (formula 3)

Now if a force with another frequency acts by the magnet coil on the system, then the system beings to oscillate with the driving frequency and not with its natural fre¬ quency. This is called a forced oscillation. The smaller the distance between the natural resonance and driving frequency, the stronger are the oscillations produced.

1 Oscillation amplitude -

1- (driving frequency/natural fre- 2 quency) (formula 4)

The object of the invention is to eliminate said disadvanta- ges with a conveyor of the type initially mentioned, so that as a rule resonance adjustment of the mass oscillating system can be dispensed with from now on, since this invention ad¬ justs to the resonance with its excitation frequency.

This object is achieved accordin_.q to the invention by the characterizing part of claim 1.

If it is possible to measure the resonance frequency, or the phase and oscillation amplitude, of the conveyor trough with a measuring device, then the excitation frequency can be adjusted to the respective resonance frequency and consequen¬ tly all problems relating to changes of masses, changes of spring constants, etc. can be avoided. The necessary excita¬ tion energy in this case is only a fraction of the previously necessary excitation energy, since now only the damping of themechanical resonant circuit must be overcome. The oscilla¬ tion amplitude also can be controlled in a simple way with the same measuring device by controlling the excitation energy.

The advantages obtained by the invention are essentially to be seen in the fact that the mechanically delicate opera¬ tions of resonance frequency adjustment are eliminated, and changes of the active masses arid spring constants no longer influence the osc.illation amplitude; also only a minimum of excitation output is required.

Finally, it is possible to work reliably and constantly with higher oscillation amplitudes, as a result of which devices of smaller dimensions than before can be used for a specific conveyor load.

The invention is explained below in greater detail by an embodiment.

In this connection, figures 1 and 2 shows representations pro¬ viding more detailed explanation of the invention;

Figure 3 shows the design of an embodiment of the oscilla¬ ting conveyor according to the invention; Figure 4 diagrammatically shows the design of the electric control and power circuit.

A conventional magnet oscillating conveyor is shown in figure 1. In this case, 1 indicates the conveyor chute,

2 the table and 3 the spring elements. The table and con¬ veyor chute together form the useful mass or useful weight. The magnet armature is indicated by 4 and the magnet coil by 5, while the countermass or stator is indicated by 6. The device rests on decoupling spring elements, especially on rubber feet 7. Spring elements 6 form, with the base of coun¬ termass 6 a spring angle of incidence 8, or °^< , while 9 indicates the projectile path of a small piece.

Figure 2 shows the relation between the oscillation ampli¬ tude and the ration of the driving frequency to the resonance frequency in the case of different dampings.

In said figure 2, the letter R indicates the resonance shift as a result of a damping change and D + G the damping and resonance influence by loading of the chute;

From figure 2 it can always be seen how in the subcritical range the influence of the additional mass coupling on the amplitude in less than in the supercritical range.

If the two frequencies coincide, i.e., if fa/fres = 1, the denominator is zero. A resonance operation with theoretical¬ ly infinitely great amplitudes is produced.

However, this operating condition is not suitable for magne¬ tic vibrators. First of all, the change of damping D + G, as occurs by diffe¬ rent materials to be conveyed or conveyor piles, results in a constant change of the oscillation width as can be seen in figure 2. Also the frequency or voltage fluctuations of the electric power supply system have too strong an effect on the oscillation width.

Further, the use of greater oscillation widths in the vici¬ nity of resonance requires setting a large air gap. However, since magnetic attraction increases in inverse proportion to the square of the air gap,, the assumptions of a constant dri¬ ving force no longer exist. Thus, a number of reasons forbid operating in the immediate vicinity of the resonance. There¬ fore, it is advisable to choose a natural frequency fe of the oscillating system that is at a certain resonance distan¬ ce from the driving frequency. Thus, the described disadvan¬ tages are partly avoided arid yet an increase of resonance of the oscillation range is attained.

Adjustment of the natural frequency is obtained by changing of the spring constants or changing of the weights, above all the useful weight.

But since in practice the spring constants are also changed by the effects of temperature, aging, etc. and above all the active masses are not constant, they change with the loa¬ ding of the conveyor trough, the object of the invention is achieved only reasonably well also in a subcritical opera¬ tional range. In addition, mechanical resonance adjustment of a 2-mass system is very time-consuming and requires great experience. In most cases the user is not capable of doing it. Today these effects on the oscillation amplitude of a conve¬ yor are partly corrected by measuring the oscillation ampli¬ tude and correcting the excitation load with a power output stage. The adjustment possibilities are, however, limited to a small part of the possibilities of the oscillating conve¬ yor.

Figure 3 corresponds to the fundamental design of a oscilla- tion conveyor of conventional construction (according to fig. l), which according to the invention was supplemented with a phase and amplitude measuring system.

The measuring system consists of a measuring coil 11 and a permanent magnet 10. If the trough oscillates perfectly, the voltage produced in the measuring coil is sinusoidal.

The produced voltage amplitude is proportional to the oscilla= tion amplitude of the trough. The crossover of the measuring voltage coincides with the maximum deviation of the trough.

The design of the electric control and power circuit is shown diagrammatically in figure 4. It consists of the following o- perating groups: - Group triac 12 which acts as an actuator for charging capa¬ citor Cl;

- Triac drive circuit 13 which provides for constant voltage on capacitor Cl;

- Rectifier 14, which transforms the ac voltage of the power supply system to a dc voltage for Cl;

- Dc energy storage 15;

- Power bridge circuit 16: if both transistors Tl and T2 be¬ come simultaneously conducting, the voltage from Cl is applied to the excitation coil of the oscillating conveyor, a current beings to flow. If the transistors are again opened and thus further rise of the coil current is interrupted, the polari¬ ty on the excitation coil immediately changes. Thus, diodes D1-D2 become conducting and recharge the decreasing coil cur¬ rent in energy storage Cl; - Permanent magnet 17 fastened to the conveyor trough;

- Measuring coil 18 which is fastened to the stator of the oscillating conveyor;

- Phase discriminator 19: the transient excitation frequen- cy and the measuring frequency are fed to it. A positive or negative voltage is formed on its output, depending on whe¬ ther the excitation frequency is greater or smaller than the resonance frequency of the oscillating conveyor;

- phase integral controller 20: it changes its output volta- ge in the correct action direction until the phase discrimi¬ nator no longer supplies any correction voltage;

- Voltage-controlled oscillator 21: it produces the excita¬ tion frequency provided by the controller;

- Measuring rectifier 23: from the measuring ac voltage it makes a dc voltage that is proportional to the amplitude of the conveyor troughj

- Amplitude controller 23: it compares the set voltage on the set-point adjuster with that from the measuring rectifi¬ er and with its output voltage drives the pulse-duration modulator;

- Pulse-duration modulator 24: it receives the correct fre¬ quency and phase position from the voltage-controlled oscil¬ lator and the information on the necessary excitation energy from the amplitude controller and makes therefrom a through- connected pulse at the correct moment and in the correct length fro transistors Tl and T2.

- Optocouplers 25:they transmit the current pulses from the control side to the power stage.

- Excitation coil 26 for driving the oscillating conveyor; - Amplitude set-point adjuster 27.

Claims

1. Device for controlling of magnetically driven mass oscil¬ lating systems, such as conveyors . or the like, in which the resonance frequencies are different and moreover can vary in any way during operation, characterized by:

a first means: consisting of a device, which can measure the resonance frequency, the phase and the oscillation amplitude of the mass oscillating system;

a second means: consisting of a control device, which in¬ dependently adjusts the excitation frequency to the natural frequency of the mass oscillating system and feeds the exci¬ tation energy at the optimal time and in the necessary amount to the magnetic drive to bring the system to the desired oscillation amplitude with minimal energy.

2. Device according to claim 1, wherein said first means consists of a measuring coil (5) and a permanent magnet (10) which are so arranged that they can measure the free oscil- lations of the system in frequency, phase and amplitude.

3. Device according to claim 1, wherein said second means is supplemented with an oscillating conveyor magnet with ar¬ mature (5, 4), in which the electric energy inductively - stored in armature coil (5) is again brought back into a ca- pacitive ener.qy storage (Cl).

4. Device according to claim 3, characterized by an electric control and power circuit, consisting of the following ope- rating groups:

- Group triac 12 which acts as an actuator for charging ca¬ pacitor Cl; - Triac drive circuit 13 which provides for constant volta¬ ge on capacitor Cl;

- Rectifier (14), which transforms the ac voltage of the power supply system to a dc voltage for Cl;

- Dc energy storage (15);

- Power bridge circuit (16): if both transistors Tl and T2 become simultaneously conducting, the voltage from Cl is applied to the excitation coil of the oscillating conveyor, a current beings to flow so that if the transistors are again opened and thus further rise of the coil current is in¬ terrupted, the polarity on the excitation coil immediately changes and diodes D1-D2 become conducting and recharge the decreasing coil current in energy storage Cl;

- Permanent magnet (17) fastened to the conveyor trough;

- Measuring coil (18) which is fastened to the stator of the oscillating conveyor;

- Phase discriminator (19): the transient excitation fre¬ quency and the measuring frequency being fed to it; a po- sitive or negative voltage being formed on its output, de¬ pending on*whether the excitation frequency is greater or smaller than the resonance frequency of the oscillating con¬ veyor-;

- Phase integral controller (20) which changes its output voltage in the correct action direction until the phase discriminator no longer supplies and correction voltage;

- Voltage-controlled oscillator (21) which produces the excitation frequency provided by the controller; - Measuring rectifier (23) which from the measuring ac volta¬ ge it makes a dc voltage that is proportional to the ampli¬ tude of the conveyor trough;

- Amplitude controller (23), which compares the set voltage on the set-point adjuster with that from the measuring rectifier and with^' its output voltage drives the pulse-dura¬ tion modulator;

- Pulse-duration modulator (24) which receives the correct frequency and phase position from the voltage-controlled - oscillator and the information on the necessary excitation energy from the amplitude controller and makes therefrom a through-connected pulse at the correct moment and in the correct length for transistors Tl and T2;

- Optocouplers (25) transmitting the current pulses from the control side to the power stage;

-Excitation coil (26) for driving the oscillating conveyor;

- Amplitude set-point adjuster (27).

5. Device according to claims 1 to 4, which is used for controlling of magnetically driven 2-mass oscillating systems.