Mixer

Details Mixer Mixer

2001-05-16

2002-12-10

Soohoo, Tony G. (Department: 1723)

Agitating

By vibration

With amplitude or frequency regulator

C366S118000, C366S332000, C366S335000, C366S601000

Reexamination Certificate

active

06491422

ABSTRACT:

OVERVIEW
This invention provides an apparatus and associated method for mixing materials, which afford exquisite control over mixing in a wide range of applications. The range extends from heavy duty agitation for preparation of concrete to delicate and precise mixing required for the pre for the preparation of pharmaceuticals and the processing of biological cultures in which living organisms must remain viable through the procedure.
The mixing of fluids involves the creation of fluid motion or agitation resulting in the uniform distribution of either heterogeneous or homogeneous starting materials that form an output product. Mixing processes are called upon to effect the uniform distribution of: miscible fluids such as ink in water; immiscible fluids such as the emulsification of oil in water; of particulate matter such as the suspension of pigment particles in a carrier fluid; mixtures of dry materials with fluids such as sand, cement and water; the chemical ingredients of oral-dosage-form pharmaceuticals; and biological specimens, such as bacteria, while growing in a nurturing media without incurring physical damage.
Mixing may be done in a variety of ways; either a rotating impeller(s) mounted onto a shaft immersed in the fluid mixture agitate(s) the fluid and/or solid materials to be mixed, or a translating perforated plate does the agitation, or the vessel itself containing the materials is agitated, shaken or vibrated. Mixing may be continuous (as when a rotating impeller is used or the containing vessel is vibrated) or intermittent as when the drive mechanism starts and stops in one or several directions.
With any conventional rotational motor, the frequency, generally measured in revolutions per minute (RPM), can be set at any value within a suitable range for different uses, but it is quite rare in fact that the RPM is varied rapidly during use. Mixers using conventional motors are set usually at one RPM, at which they run for the duration of the mixing. Sometimes the RPM may be varied during mixing, but it is either continuously changed slowly or incremented only a few times. The RPM is not usually incremented continuously or over a large number of RPM changes.
With a conventional vibrational mixer, the amplitude can be varied within very narrow limits, and the frequency is generally set at the frequency of the AC power source. Even when using a motor controller with frequency control, the vibrational frequency of a conventional vibrational mixer can be varied only within relatively narrow limits.
When biological tissue is cultivated, all cells must stay suspended in the nutrient broth; that is, the cells should not sediment to the bottom of the vessel in which they are cultivated. However, in agitating living cells so as to minimize sedimentation, the mechanical effect of the agitator should not compromise the integrity of the cells. In the case of rotating agitators, quite often the culture medium creates a turbulent vortex into which the cells are sucked. Under the turbulent vortex conditions, the cells are at greater risk of being mechanically damaged and the continuous supply of oxygen to the cells is not consistently assured.
The present invention provides a vibration mixer driven by an electronically controllable motor, adapted so as to allow virtually unlimited control of the mixing process. To accomplish this, the present invention builds on the developments of U.S. Pat. No. 5,033,321 issued to D. Gerson (the “Gerson Patent”), hereby incorporated by reference in its entirety.
The Gerson patent concerns an apparatus and method for measuring the degree or rate of mixing during the mixing process. The Gerson patent discloses a closed-loop feedback system for use with then available vibration mixers. The Gerson system comprises a sensor that detects certain physical or chemical parameters that indicate the degree of mixing, i.e., the degree of turbulence, which in turn provides a quantitative measure of the degree of homogeneity of the mixed fluid. Through a feedback loop of testing when the key parameters achieve certain values, the Gerson sensor aids in determining that the mixing has achieved a desired level of homogeneity. In developing the feedback system, the Gerson patent reveals that optimal mixing results are achieved by simultaneously adjusting both the amplitude and the frequency of the vibration mixing device. However, the heretofore available vibration mixers have not readily allowed the simultaneous and independent adjustment of both the amplitude and the frequency of vibration in order to take advantage of the Gerson technology. The heretofore available vibration mixers have been restricted to a narrow range of both frequencies and amplitudes. Thus, the present invention provides a vibration mixer that can take ready advantage of the Gerson technology.
In accordance with the present invention, a vibration mixer comprises a motor, controlled by an electronic controller, and an agitator, driven by the motor to agitate a fluid to be mixed; this fluid is sometimes hereinafter called the “mixant.” The mixant, which may be entirely liquid or may contain particulates with or without liquid, or foam, generally starts out heterogeneous and is intended to be made at least somewhat more homogeneous. Alternatively, in other embodiments, the mixant is a fluid that is to be agitated in order to maintain a desired state of homogeneity or to aerate or circulate nutrients in a biological fermenter, or the like.
The present invention permits independent and simultaneous adjustment of both the frequency and the amplitude of a vibrational mixer thereby allowing almost unlimited control of the mixing process. Additionally, this invention permits the adjustment of the vibrational rate from extremely low frequencies to frequencies in the order of 10 Hz or greater. Furthermore, this invention permits the adjustment of the amplitude of vibrational travel from micrometers to meters, depending on the size and scale of the mixer vessel. Additionally, this invention permits the adjustment of the waveform of the vibrational mixing to sinusoidal, pulsatile, square-wave, or to a complex waveform, any of which can be programmed into the control unit.
There are numerous alternative embodiments of the vibration mixer of the present invention, any and all of which can be selected depending on the user's needs and the mixing process being performed. One embodiment is a configuration to provide up and down (or alternatively a horizontal back and forth) oscillatory motion of the agitator to bring about the desired mixing. In still another embodiment the mixer may be configured to provide discrete steps in rotational motion to effect the desired mixing.
Where the motor provides rotational motion, as by a stepper motor, the rotational velocity, or instantaneous RPM, may be caused to change rapidly many times during each revolution or up-and-down oscillation. In this invention, an operator may program the changes at will RPM so as to create any step-by-step pattern desired. In comparison to a conventional rotational mixer, the instantaneous RPM can be varied in very small intervals of time and rotation, such that one rotational step can be fast or slow, or forwards or backwards, within broad limits.
In accordance with the present invention, the motor may be a linear motor, a stepper motor or a DC continuous motor. Selection of the preferred motor may depend on the agitating profile which may include, for example, the speed, the direction, the continuity or intermittency of agitation, and the amount of energy required to agitate the mixant to the degree appropriate to the task.
The agitator may be, for example, an impeller driven in a circular motion, a perforated stirrer plate moved translationally, or some other means for agitating the mixant. As it relates to a vessel in which the mixant is contained, such an impeller or stirrer plate may have a diameter almost equal to that of the vessel or extend only a small percentage of the cross-sectional area of the vessel. Optionally, s

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