U.S. patent application number 11/840698 was filed with the patent office on 2007-12-06 for resonant shaking.
This patent application is currently assigned to Bose Corporation, a Delaware corporation. Invention is credited to Ricardo F. Carreras.
Application Number | 20070280036 11/840698 |
Document ID | / |
Family ID | 36912523 |
Filed Date | 2007-12-06 |
United States Patent
Application |
20070280036 |
Kind Code |
A1 |
Carreras; Ricardo F. |
December 6, 2007 |
Resonant Shaking
Abstract
A resonant shaker includes a support tray for supporting a
target carrier. A sensor generates an electrical signal that is
related to an acceleration of the support tray. A linear drive
motor includes an armature that is coupled to the support tray. The
linear drive motor provides an oscillating drive force to the
support tray in response to a drive current applied to the linear
drive motor. The resonant shaker also includes a controller. The
controller receives the electrical signal from the sensor and a
drive signal that is related to the drive current. The controller
transmits a modified drive current to the linear drive motor in
response to a predetermined phase relationship between the
electrical signal and the drive signal.
Inventors: |
Carreras; Ricardo F.;
(Southborough, MA) |
Correspondence
Address: |
FISH & RICHARDSON PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
Bose Corporation, a Delaware
corporation
|
Family ID: |
36912523 |
Appl. No.: |
11/840698 |
Filed: |
August 17, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11063367 |
Feb 23, 2005 |
7270472 |
|
|
11840698 |
Aug 17, 2007 |
|
|
|
Current U.S.
Class: |
366/116 |
Current CPC
Class: |
B01F 11/0022 20130101;
B01J 2219/0024 20130101; B01J 2219/00207 20130101; Y10S 366/601
20130101; B06B 1/0261 20130101; B01J 19/285 20130101; B01J
2219/00191 20130101 |
Class at
Publication: |
366/116 |
International
Class: |
B01F 11/00 20060101
B01F011/00 |
Claims
1. A method for use in connection with mixing of materials that
have been loaded into a structure, the method comprising:
identifying a mechanical resonance frequency of the loaded
structure, and automatically controlling a driving frequency of an
actuator to cause the structure to shake at a shaking frequency
that has a predefined relationship to the mechanical resonance
frequency.
2. The method of claim 1 in which controlling the driving frequency
comprises: changing the driving frequency to maintain the
predefined relationship in response to a change in the identified
mechanical resonance frequency.
3. The method of claim 1 wherein the controlling comprises closed
loop control.
4. The method of claim 1 wherein causing the structure to shake
comprises causing the structure to shake substantially only along a
particular axis.
5. The method of claim 1 wherein causing the structure to shake
comprises causing the structure to shake vertically.
6. The method of claim 1 wherein causing the structure to shake
comprises causing the structure to shake horizontally.
7. The method of claim 1 wherein the actuator comprises a linear
actuator.
8. The method of claim 1 wherein the predefined relationship
comprises having the shaking frequency be equal to the mechanical
resonance frequency.
9. The method of claim 1 wherein the predefined relationship
comprises having the shaking frequency be near to the mechanical
resonance frequency.
10. A method for use in connection with mixing of materials that
have been loaded into a structure, the method comprising:
identifying a mechanical resonance frequency of the loaded
structure, and automatically controlling via closed loop control a
driving frequency of an actuator to cause the structure to shake
vertically at a shaking frequency that has a predefined
relationship to the mechanical resonance frequency.
Description
[0001] This application is a continuation and claims the benefit of
priority under 35 USC 120 of U.S. application Ser. No. 11/063,367,
filed Feb. 23, 2005. The disclosure of the prior application is
considered part of and is incorporated by reference in the
disclosure of this application.
BACKGROUND OF THE INVENTION
[0002] Processing materials, such as biological materials or
chemical materials often requires the mixing of these materials
within a container. The container can be a test tube or beaker, for
example. A rack that supports multiple containers is sometimes used
when mixing batches of materials. Mixing can be achieved by shaking
the container or by using a stirring rod or impeller immersed in
the material. Some mixers use a coated magnet placed inside the
container. The coated magnet is magnetically driven in a rotary
motion to mix the contents of the container. Non-invasive mixers,
such as shakers, can be advantageous because they do not introduce
stirrers, mixing blades, or other mechanical devices into direct
contact with the materials to be mixed, thus avoiding potential
contamination of those materials by the blades or other mechanical
devices.
SUMMARY OF THE INVENTION
[0003] In one aspect, the invention is embodied in a resonant
shaker. The resonant shaker includes a support tray for supporting
a target carrier. A sensor generates an electrical signal that is
related to an acceleration of the support tray. The sensor can be
attached to the support tray. A linear drive motor includes an
armature that is coupled to the support tray. The linear drive
motor provides an oscillating drive force to the support tray in
response to a drive current applied to the linear drive motor. The
resonant shaker also includes a controller. The controller receives
the electrical signal from the sensor and a drive signal that is
related to the drive current. The controller transmits a modified
drive current to the linear drive motor in response to a
predetermined phase relationship between the electrical signal and
the drive signal.
[0004] The linear drive motor can provide a reciprocating motion to
the support tray. The target carrier can be a bioreactor chamber.
Alternatively, the support tray can be integrated with a
bioreactor. The target carrier can be a beaker, a test tube, and a
multiple tube rack. The target carrier can contain a specimen
including a chemical material, a biological material, a cell
culture, a tissue, and a tissue construct. The specimen can include
a particulate substance, a slurry, and a fluid.
[0005] The armature of the linear drive motor can be coupled to the
support tray through an elastic element. In this configuration, the
predetermined phase relationship is an absolute value of a
difference in phase between the electrical signal and the drive
signal of substantially ninety-degrees. Alternatively, the armature
can be coupled to the support tray through a rigid coupling. An
elastic element can be coupled between the support tray and a
housing of the linear drive motor. In this configuration, the
predetermined phase relationship is an absolute value of a
difference in phase between the electrical signal and the drive
signal of substantially zero-degrees.
[0006] In one configuration, the desired shaking frequency of the
specimen causes the combination at least two materials. In one
configuration, the desired shaking frequency of the specimen causes
the separation of at least two materials. The desired shaking
frequency can be a resonant frequency of movable elements of the
resonant shaker.
[0007] The elastic element can be a grommet, a torsional spring, a
coil spring, a leaf spring, a disc spring, an elliptical spring, a
helical spring, an air spring, or a cantilever spring.
[0008] In one aspect, the controller controls at least one of a
frequency and an amplitude of an oscillation of the armature of the
linear drive motor. An amplitude of a modified drive current
applied to the linear drive motor displaces the armature of the
linear drive motor by a predetermined amount. A phase detector can
be integrated with the controller.
[0009] The controller can adjust a frequency of the drive current
in response to the predetermined phase relationship between the
electrical signal and the drive signal. The controller can modify
at least one of a frequency and an amplitude of the drive current
based on a measure of viscosity of the specimen.
[0010] The sensor can be attached to the support tray, the
armature, or the target carrier. The sensor can be a position
sensor, a velocity sensor, a jerk sensor, or an accelerometer. In
addition to acceleration, the electrical signal from the sensor can
be related to at least one of a displacement of the support tray, a
velocity of the support tray, and a jerk of the support tray. The
sensor can be an optical sensor.
[0011] In another aspect, the invention is embodied in a method of
shaking using a resonant shaker. The method includes oscillating a
support tray of the resonant shaker with a linear drive motor that
is driven by a drive current and generating a drive signal that is
related to the drive current. The method further includes
generating an electrical signal that is related to an acceleration
of the support tray. The drive current is modified in response to a
predetermined phase relationship between the electrical signal and
the drive signal to generate a modified drive current. The linear
drive motor is driven with the modified drive current to oscillate
the support tray. The support tray can be oscillated at a resonant
frequency of the system. The method can further include loading a
target carrier containing the specimen onto the support tray of the
resonant shaker.
[0012] The modified drive current can control an amplitude of an
oscillation and/or a frequency of an oscillation of the support
tray. The support tray can be displaced by a predetermined
amount.
[0013] The support tray can be coupled to the linear drive motor
through an elastic element. In this configuration, the
predetermined phase relationship is an absolute value of a
difference in phase between the electrical signal and the drive
signal of substantially ninety-degrees. Alternatively, the support
tray can be coupled to the linear drive motor through a rigid
coupling. An elastic element can be coupled between the support
tray and a housing of the linear drive motor. In this
configuration, the predetermined phase relationship is an absolute
value of a difference in phase between the electrical signal and
the drive signal of substantially zero-degrees.
[0014] The desired shaking frequency can be a resonant frequency of
movable elements of the resonant shaker. Modifying the drive
current can include adjusting a frequency of the drive current in
response to the predetermined phase relationship between the
electrical signal and the drive signal.
[0015] Modifying the drive current can include adjusting at least
one of a frequency and an amplitude of the drive current based on a
measure of viscosity of the specimen. Additionally, modifying the
drive current can include adjusting at least one of a frequency and
an amplitude of the drive current based on a measure of a PH value
of the specimen. Modifying the drive current can include adjusting
at least one of a frequency and an amplitude of the drive current
based on a measure of temperature of the specimen.
[0016] In addition, modifying the drive current can include
adjusting at least one of a frequency and an amplitude of the drive
current based on a measure of turbulence of the specimen. Modifying
the drive current can include adjusting at least one of a frequency
and an amplitude of the drive current based on a measure of
conductivity of the specimen. In addition, modifying the drive
current can include adjusting at least one of a frequency and an
amplitude of the drive current based on a measure of resistivity of
the specimen. Modifying the drive current can include adjusting at
least one of a frequency and an amplitude of the drive current
based on a measure of chemical composition of the specimen.
[0017] In another aspect, the resonant shaker can include a support
tray for supporting a target carrier. A linear drive motor includes
an armature that is coupled to the support tray. The linear drive
motor provides an oscillating drive force to the support tray in
response to a drive current applied to the linear drive motor. A
controller is electrically coupled to the linear drive motor. The
controller receives a signal that is indicative of a measured
parameter of the linear drive motor. The controller transmits a
modified drive current to the linear drive motor in response to the
signal.
[0018] The measured parameter can include an input impedance of the
linear drive motor. The measured parameter can also include at
least one of an input current, input power, or input voltage to the
linear drive motor. The measured parameter can include at least one
of a displacement, a velocity, an acceleration, and a jerk of the
armature of the linear drive motor.
[0019] A sensor can be coupled to the support tray. The target
carrier can contain a specimen that is chosen from the group
comprising a chemical material, a biological material, a cell
culture, a tissue, and a tissue construct. The target carrier can
contain a specimen that is chosen from the group comprising a
particulate substance, a slurry, and a fluid. In one embodiment, a
frequency of oscillation of the support tray causes the combination
at least two materials. In one embodiment, a frequency of
oscillation of the support tray causes the separation of at least
two materials.
[0020] The armature can be coupled to the support tray through an
elastic element. Alternatively, the armature can be coupled to the
support tray through a rigid coupler. In this configuration, an
elastic element is coupled between the support tray and a housing
of the linear drive motor. The controller can control at least one
of a frequency and an amplitude of an oscillation of the armature
of the linear drive motor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 illustrates a block diagram of a system for shaking a
specimen according to the invention.
[0022] FIG. 2 illustrates a flowchart of a process of shaking a
specimen according to the invention.
[0023] FIG. 3 illustrates a block diagram of a resonant shaker
according to the invention.
[0024] FIG. 4 is a graphical representation of phase response as a
function of frequency for the resonant shaker of FIG. 3.
[0025] FIG. 5 illustrates a block diagram of another resonant
shaker according to the invention.
[0026] FIG. 6 is a graphical representation of phase response as a
function of frequency for the resonant shaker of FIG. 5.
DETAILED DESCRIPTION
[0027] Processing chemical materials, biological materials, and
other materials, such as screws, nails, nuts, and bolts, and/or
particulates or fluids often requires the mixing or separating of
materials within a container. An apparatus according to the
invention can effectively shake a specimen at a desired frequency.
The desired frequency can be the resonant frequency of the system
including the container or target carrier containing the specimen
to be mixed. The resonant frequency of the system can provide
efficient mixing or separating of the specimen while minimizing the
input energy required to maintain the mixing or separating. The
apparatus is generally configured for use in a vertical dimension,
but can also be configured for use in a horizontal dimension.
[0028] The apparatus can automatically adjust the amplitude and/or
the frequency of the shaking mechanism as properties of the
specimen change during the shaker (e.g., viscosity, mass,
temperature, PH value, resistivity, conductivity, etc.).
Additionally, to achieve significant leverage from the motor, the
mechanical system can be designed as a resonant structure with a
high Q value. This can make the system sensitive to small changes
in the properties of the specimen and/or the mechanical system. The
closed-loop control scheme can employ a feedback circuit. To
automatically adjust the amplitude and/or the frequency of the
shaking mechanism, the closed-loop control scheme is used to
maintain the system driven near resonance despite changes in the
target specimen or the mechanical system. For example, depending on
the system configuration, the phase relationship between a signal
that is related to a characteristic of the movable elements of the
system (e.g., displacement, velocity, acceleration, and/or jerk)
and a drive signal applied to the driving motor of the system can
be used to determine a desired shaking frequency of the specimen
(i.e., the resonant frequency of the system).
[0029] In other configurations, a linear drive motor provides an
oscillating drive force to a support tray in response to a drive
current applied to the linear drive motor. A controller is
electrically coupled to the linear drive motor. The controller
receives a signal that is indicative of the measured parameter of
the linear drive motor. The signal can be generated by a load
sensor, such as an ohm meter, for example. The controller transmits
a modified drive current to the linear drive motor in response to
the measured parameter. The modified drive current applied to the
linear drive motor can drive the movable elements of the system
near resonance despite changes in the target specimen or the
mechanical system.
[0030] The measured parameter can include an input impedance of the
linear drive motor, for example. In this embodiment, the behavior
of the impedance load of the linear drive motor can be measured at
the input terminals of the motor. The behavior of the impedance
load can be related to the resonance of the moving elements of the
system.
[0031] The measured parameter can also include at least one of an
input current, input power, or input voltage to the linear drive
motor. The measured parameter can include at least one of a
displacement, a velocity, an acceleration, and a jerk of the
armature of the linear drive motor.
[0032] The resonant shaker of the present invention can be used to
cause the mixing or combination of two or more media (including
liquids, gases, and solids) either as an intermediate material or
as a final product.
[0033] Additionally, the resonant shaker can be used to separate
materials in a resonant separation application. A resonant
separation application includes applications intended to cause
sifting, filtering, sorting, cleaning, dividing, and/or isolating
of two or more media (including liquids, gases and solids) either
as an intermediate material or as a final product. For example, the
material or specimen can be a particulate substance, a slurry, or a
fluid.
[0034] The resonant shaker can be used to promote cell culturing
which can include the cultivation of cells in the laboratory.
Cultures must provide sources of energy and raw material for
biosynthesis, as well as a suitable physical environment. Cultures
isolated from nature are usually mixed; pure cultures are best
obtained by subculturing single colonies. Viruses are often grown
in cultures of a host cell, and may be isolated as plaques in a
continuous lawn of those cells.
[0035] In ordinary cultures the cells are at all possible stages in
their division cycle and the composition of the medium changes
continually as a result of their metabolism (until growth ceases,
in the stationary phase of the culture). On transfer of a
relatively minute number of cells (e.g., inoculum) to fresh medium,
there may be a lag phase, without multiplication, followed by a
phase of exponential growth. Synchronous cultures are achieved by
blocking growth or harvesting cells at a specific stage; the cells
then divide in synchrony for several generations. In continuous
cultures, fresh medium flows into the vessel and full-grown culture
flows at the same rate (such as in a chemostat); the cells are
therefore harvested from a medium of constant composition.
Laboratory cultures are often made in small flasks, test tubes, or
covered flat dishes (petri dishes). Industrial cultures for
antibiotics or other microbial products are usually in fermentors
of 10,000 gallons (37,850 liters) or more. The resonant shaker can
separate the cells from the culture fluid by centrifugation or
filtration.
[0036] Specific procedures are employed for isolation, cultivation,
and manipulation of microorganisms, including viruses and
rickettsia, and for propagation of plant and animal cells and
tissues. The inoculum is introduced into a sterilized nutrient
environment, the medium. The culture medium in a suitable vessel or
target carrier is protected by cotton plugs or loose-fitting covers
with overlapping edges so as to allow diffusion of air and to also
prevent access of contaminating organisms from the air or from
unsterilized surfaces. The transfer, or inoculation, usually is
done with the end of a flamed, then cooled, platinum wire. Sterile
swabs may also be used and, in the case of liquid inoculum, sterile
pipets.
[0037] The aqueous solution of nutrients may be left as a liquid
medium or may be solidified by incorporation of a nutritionally
inert substance, most commonly agar or silica gel. Special gas
requirements may be provided in culture vessels closed to the
atmosphere, as for anaerobic organisms. Inoculated vessels are held
at a desired constant temperature in an incubator or water bath.
The resonant shaker can mechanically agitate the liquid culture
media during incubation. Maximal growth, which is visible as a
turbidity or as masses of cells, is usually attained within a few
days, although some organisms may require weeks to reach this
stage.
[0038] Cell culturing may be used for the purpose of, for example,
the production of useful products such as proteins, recombinant
proteins, metabolites, secondary metabolites, monoclonal
antibodies, and pharmaceuticals. Cell culturing may also be used to
produce useful quantities of cells for medical or therapeutic
applications.
[0039] Cell culturing can also include direct or indirect actuation
of cells organized into tissues or tissue constructs. The term
"direct actuation" means the application of stress, strain, flow,
temperature or nutrient environment to cells or tissues within a
bioreactor chamber. The term "indirect actuation" means the
mechanical excitation of an entire chamber containing cells or
tissues. Thus, the resonant shaker can be used to process chemical
materials, biological materials, cell cultures, and/or tissues or
tissue constructs through indirect actuation.
[0040] FIG. 1 illustrates a block diagram of a system 100 for
shaking a specimen 102 according to the invention. The system 100
includes a support tray 104 that is configured to support a target
carrier 106 containing the specimen 102. The support tray 104 is
coupled to an armature 107 of a linear drive motor 108 through a
coupler 110. The coupler 110 can rigidly couple the support tray
104 to the armature 107 of the linear drive motor 108. In this
configuration, optional members 111 can be positioned between the
support tray 104 and a housing 112 of the linear drive motor 108.
The optional members 111 can be elastic elements, such as springs,
for example.
[0041] Alternatively, the coupler 110 can couple the support tray
104 to the armature 107 of the linear drive motor 108 through an
elastic element, such as a spring (not shown). In this
configuration, optional members 111 can be positioned between the
support tray 104 and the housing 112 of the linear drive motor 108.
Here, the optional members 111 can be guide rods that guide and
stabilize the support tray 104, for example. The optional members
111 can be slides, telescoping members, or any other mechanism that
guides and stabilizes the support tray 104. The optional members
111 can also be elastic elements, such as springs. Various
techniques for coupling the support tray 104 to the armature 107 of
the linear drive motor 108 are described in more detail herein.
[0042] The specifications and requirements of the linear drive
motor 108 can change depending on the coupling between the armature
107 of a linear drive motor 108 and the support tray 104. For
example, when the coupling between the armature 107 of a linear
drive motor 108 and the support tray 104 is through an elastic
element, the linear drive motor 108 should exhibit relatively high
force coupled with relatively low displacement. Conversely, when
the coupling between the armature 107 of a linear drive motor 108
and the support tray 104 is through a rigid coupler, the linear
drive motor 108 should exhibit relatively low force coupled with
relatively high displacement.
[0043] A controller 113 is electrically coupled to an amplifier
114. The amplifier 114 is electrically connected to the linear
drive motor 108. The amplifier 114 receives a drive control signal
from the controller 113 and provides a drive current to the linear
drive motor 108. In addition to providing a drive control signal,
the controller 113 can also provide signal conditioning and phase
detection, which is described in more detail herein.
[0044] The controller 113 can include a phase detector 116, an
analog-to-digital (A/D) converter 118, a microprocessor 120, and a
digital-to-analog (D/A) converter 122. The components 116, 118,
120, and 122 can be configured in a different manner. Additionally,
the controller 113 can include various other components.
Alternatively, the controller can encompass different components
than shown.
[0045] A sensor 124 is rigidly attached to the support tray 104.
The sensor 124 can be a position sensor, a velocity sensor, an
accelerometer, or a jerk sensor, for example. The sensor 124 is
electrically coupled to the controller 113. The sensor 124 provides
an electrical signal to the controller 113. The electrical signal
can be related to the displacement, velocity, acceleration and/or
jerk of the support tray 104. The sensor 124 can include any sensor
that provides position, velocity, acceleration, or jerk information
relating to the support tray. For example, the sensor 124 can
include an electrical sensor, an electromechanical sensor, an
electro-fluidic sensor, or an optical sensor.
[0046] In one configuration, the sensor 124 is an accelerometer
that generates an acceleration signal. The acceleration signal can
be used to generate other information (besides acceleration) about
the support tray 104. For example, the integration of an
acceleration signal results in a velocity signal and the
integration of a velocity signal results in a displacement signal.
Thus, when the sensor 124 is an accelerometer, the controller 113
can use acceleration, velocity or displacement of the support tray
104 as a measurement parameter. However, when processing a
waveform, it is generally desirable to include high-frequency
information. When integrating a signal from acceleration to
velocity, the high-frequency response is generally reduced in level
due to approximations in the integration (i.e., through the use of
a low-pass filter). Thus, many small irregularities in the waveform
can disappear.
[0047] Additionally, the sensor 124 can be any type of
accelerometer. For example, the accelerometer can be a seismic
instrument, such as a translational accelerometer which measures
acceleration without regard to a reference point. In general, the
type of sensing device used to measure the acceleration determines
whether the accelerometer is considered a mechanical or
electromechanical device. One type of mechanical accelerometer
includes a liquid-damped cantilever spring-mass system. In an
electromechanical device, the type of electromechanical sensing
device classifies the accelerometer as a variable resistance,
variable inductance, piezoelectric, piezotransistor, or servo type
of instrument or transducer.
[0048] A current sensor 126 is coupled between the amplifier 114
and the linear drive motor 108. The current sensor 126 measures the
drive current supplied to the linear drive motor 108 by the
amplifier 114. The current sensor 126 is electrically coupled to
the controller 113 and provides a drive signal to the controller
113. In one embodiment, a voltage sensor (not shown) is used to
measure the voltage supplied to the linear drive motor 108. The
voltage sensor could be electrically coupled to the controller 113
and could provide a voltage signal to the controller 113.
[0049] A power supply 128 is electrically coupled to the controller
113. The power supply 128 can be an alternating current (AC) power
supply, a direct current (DC) power supply or a radio-frequency
(RF) power supply. The power supply 128 is configured to supply
power to the controller 113.
[0050] The system 100 can also include a display 130 that is
coupled to the controller 113. The display 130 can be used to
display data relating to properties of the specimen 102 as well as
data relating to properties of the system 100, such as the
frequency and amplitude of the shaking process. A keypad 132 can
also be coupled to the controller 113. The keypad 132 can be used
to input control parameters into the controller 113 to control the
system 100. For example, the control parameters can include on/off,
time, frequency, and/or amplitude of the shaking process.
[0051] The system 100 can also include a computer 134 that is
coupled to the controller 113. The computer 134 can control the
system 100 from a remote location, for example. Additionally, the
computer 134 can collect and store data relating to the process,
such as data from the sensor 124, data from the current sensor 126,
and/or data from sensors (not shown) that monitor the specimen 102,
for example.
[0052] The system 100 can be connected to the computer 134 via a
network, such as a local area network (LAN) (not shown). In this
configuration, the computer 134 can be used to control and collect
data from several systems 100 to facilitate batch processing for
example.
[0053] The system 100 processes the specimen 102 using the
following general operating principles. The specific operating
principles of the system 100 generally depend on the specific
system configuration and are described in more detail herein. The
target carrier 106 containing the specimen 102 is loaded onto the
support tray 104. The system 100 is activated through functions on
the keypad 132 or the computer 134. Once the system 100 is
activated, the linear drive motor 108 begins oscillating the
support tray 104 at a predetermined frequency.
[0054] The sensor 124 measures a specific parameter of the moving
support tray 104. For example, in one configuration, the sensor 124
is an accelerometer that measures an acceleration of the support
tray 104. The sensor 124 transmits an electrical signal that is
related to the acceleration of the support tray 104 to the phase
detector 116. The phase detector 116 is shown integrated with the
controller 113, but can alternatively embody a separate
component.
[0055] The current sensor 126 measures the drive current supplied
to the linear drive motor 108 by the amplifier 114. A drive signal
from the current sensor 126 representative of the drive current is
transmitted to the phase detector 116.
[0056] The phase detector 116 can measure the phase between two
independent input signals. For example, the phase detector 116 can
measure the absolute value of a difference in phase between the
electrical signal and the drive signal. The resonant frequency of
the system is related to the phase relationship between the
electrical signal and the drive signal. In one configuration, the
resonant frequency of the system is reached when the absolute value
of the difference in phase between the electrical signal (i.e., the
signal from the accelerometer) and the drive signal (i.e., the
measured drive current that drives the linear drive motor 108) is
maintained at ninety-degrees. This phase relationship assumes that
the armature 107 of the linear drive motor 108 is coupled to the
support tray 104 through an elastic element, such as a spring, for
example.
[0057] In one embodiment, the sensor 124 is a velocity sensor. In
this embodiment, the sensor 124 transmits an electrical signal to
the phase detector 116 that is related to the velocity of the
support tray 104. The resonant frequency of the system is reached
when the absolute value of the difference in phase between the
electrical signal (i.e., the signal from the velocity sensor) and
the drive signal (i.e., the measured drive current that drives the
linear drive motor 108) is maintained at zero-degrees or
180-degrees. This phase relationship assumes that the armature 107
of the linear drive motor 108 is coupled to the support tray 104
through an elastic element, such as a spring, for example.
[0058] In another embodiment, the sensor 124 is a displacement
sensor that transmits an electrical signal to the phase detector
116 that is related to the displacement of the support tray 104.
The resonant frequency of the system is reached when the absolute
value of the difference in phase between the electrical signal
(i.e., the signal from the position sensor) and the drive signal
(i.e., the measured drive current that drives the linear drive
motor 108) is maintained at ninety-degrees. This phase relationship
assumes that the armature 107 of the linear drive motor 108 is
coupled to the support tray 104 through an elastic element, such as
a spring, for example.
[0059] The phase detector 116 transmits an analog signal to the A/D
converter 118 that is related to the phase relationship between the
electrical signal and the drive signal. The A/D converter 118
converts the analog signal to a digital signal and transmits the
digital signal to the microprocessor 120. The microprocessor 120
generates a modified drive control signal having a different
frequency and/or amplitude than the instant drive control signal to
modify the phase relationship between the electrical signal and the
drive signal. The modified drive control signal is converted to an
analog signal by the D/A converter 122. The modified drive control
signal is transmitted by the controller 113 to the amplifier 114.
The amplifier 114 converts the modified drive control signal to a
drive current that is suitable for driving the linear drive motor
108.
[0060] In general, for a shaker having multiple masses and multiple
spring elements, the phase relationship between the drive signal
and the acceleration signal can be complex. The techniques taught
herein can be used in such complex systems. In many of these
complex systems, the signals can have approximately a monotonic
phase relationship over a desired frequency range of the drive
signal.
[0061] In one embodiment, the system 100 uses a "hunting" algorithm
to determine and maintain the appropriate frequency that drives the
linear drive motor 108 in order to shake the specimen at the
resonant frequency of the moving elements of the system 100. The
hunting algorithm is described in more detail herein. It should be
noted that there are various other techniques that can be used to
determine and maintain the drive frequency, such as by measuring
and monitoring the displacement of the armature 107 and/or the
support tray 104 and transmitting the displacement measurement to
the controller 112. Other techniques can involve monitoring the
drive current supplied to the linear drive motor using a feedback
mechanism and/or monitoring another parameter of the system and
supplying the monitored information to the controller 112.
[0062] FIG. 2 illustrates a flowchart 200 of a process of shaking a
specimen 102 (FIG. 1) according to the invention. In a first step
202, the target carrier 106 (FIG. 1) containing the specimen 102 is
initially loaded onto the support tray 104 (FIG. 1). In a second
step 204, the controller 113 transmits a drive current having a
first frequency to the linear drive motor 108 to oscillate the
support tray 104 at the first frequency. The first frequency is a
low frequency that is below the target resonant frequency of the
system.
[0063] In a third step 206, the sensor 124 measures the
acceleration of the support tray 104 and generates an electrical
signal. The controller 113 receives the electrical signal that
corresponds to the measured acceleration of the support tray 104.
Additionally, the current sensor 126 measures the drive current and
generates a drive signal. The controller 113 receives the drive
signal that corresponds to the measured drive current. The
measurement of the acceleration of the support tray 104 and the
measurement of the drive current can occur simultaneously or in any
order, providing that the phase relationship between the electrical
signal and the drive signal is significantly preserved.
[0064] In a fourth step 208, the phase detector 116 which, in this
example, is integrated with the controller 113, measures the phases
of the drive signal and the electrical signal. The phase detector
116 then waits for the phase measurement to stabilize. For example,
the wait time is generally proportional to the Q of the system.
Thus, for a high Q system, the wait time for the phase measurement
to stabilize is generally longer than a wait time for a system
having a lower Q.
[0065] In a fifth step 210, the controller 113 compares the
absolute value of the difference in phase between the drive signal
and the electrical signal. If the absolute value of the difference
in phase between the drive signal and the electrical signal equals
ninety-degrees (the value of the difference in phase depends on the
system configuration), the mixing process proceeds using the
instant drive current according to a sixth step 212. The instant
drive current applied to the linear motor causes the movable
elements of the system to oscillate at the resonant frequency. The
controller 113 continues to monitor the acceleration of the support
tray 104 and the drive current supplied to the linear drive motor
108 according to step 206 in the event that system disturbances
and/or drifts drive the system out of resonance.
[0066] If the absolute value of the difference in phase between the
drive signal and the electrical signal does not equal
ninety-degrees (for this system configuration), the drive current
is modified according to a seventh step 214. The controller 113
modifies the drive current according to a "best-guess" hunting
algorithm that is discussed in more detail herein.
[0067] In one embodiment, the algorithm determines whether the
phase is above or below ninety-degrees. The absolute value of the
difference is used when the system is configured to use a phase
difference of zero-degrees or 180-degrees. Thus, at the fifth step
210 the controller 113 checks to see if the difference in phase is
above or below ninety-degrees. If the difference in phase is above
ninety-degrees, then the controller 113 decreases the frequency of
the drive current. If the difference in phase is below
ninety-degrees, then the controller 113 increases the frequency of
the drive current.
[0068] The controller 113 applies the modified drive current to the
linear drive motor 108 which oscillates the support tray according
to an eighth step 216. The modified frequency of the oscillation
changes the measurement of the acceleration from the sensor 124. In
step 206, the phase detector 116 measures the phases of the
modified drive signal and the electrical signal corresponding to
the new value of the acceleration of the support tray 104.
[0069] This loop continues until a predetermined phase relationship
between the electrical signal from the sensor 124 (e.g., the
accelerometer) and the drive signal from the current sensor 126 is
achieved. In one embodiment, the predetermined phase relationship
corresponds to the resonant frequency of the moving elements of the
system 100. The system can be driven off resonance by allowing the
user to set the desired phase set-point to a value other than the
value corresponding to the predetermined phase relationship.
[0070] FIG. 3 illustrates a block diagram of a resonant shaker 300
according to the invention. The resonant shaker 300 includes an
enclosure 302 that houses a power supply 304, a controller 306 and
a linear drive motor 308. The enclosure 302 can also include feet
309. The feet 309 can be composed of an elastic material, such as
rubber, to dampen vibrations from the resonant shaker 300 and to
prevent the resonant shaker 300 from moving in a lateral direction
during operation. Other suitable materials can also be used to
reduce vibration and/or prevent the resonant shaker 300 from moving
during operation. The resonant shaker 300 can also include an
optional analyzer 310 that can analyze certain properties of a
specimen 311 contained within a target carrier 312. The resonant
shaker 300 is generally placed on a solid surface 313 such as a
table, a pedestal, a floor, or a shelf.
[0071] The power supply 304 is configured to supply power to the
controller 306, the analyzer 310, and any other necessary and/or
optional components. For example, the power supply 304 supplies
power to the controller 306 through a power transmission line 313.
Similarly, the power supply 304 supplies power to the analyzer 310
through a power transmission line 314.
[0072] The controller 306 couples power to the linear drive motor
308 through a power transmission line 316. A current sensor 318 is
coupled to the power transmission line 316. The current sensor 318
measures the drive current supplied to the linear drive motor 308
and generates a drive signal. The current sensor 318 communicates
the drive signal to the controller 306 through a signal
transmission line 320.
[0073] The linear drive motor 308 includes an armature 322 that is
coupled to a support tray 324 through an elastic element 326, such
as a spring. The elastic element 326 can include, but is not
limited to, a coil spring, a leaf spring, a torsional spring, a
disk spring, an elliptic spring, a helical spring, an air spring, a
cantilever spring, a rubber element, such as a grommet, or any
element that stores energy as a function of displacement and when
released, eventually recovers its basic form and position.
Additionally, one or more optional guide rods 325 can be used to
guide and stabilize the support tray 324. In this configuration,
the support tray 324 can include bearings (not shown) that ride on
the guide rods 325.
[0074] Although the system 300 is shown having an elastic element
326 including a single coil spring that couples the armature 322 to
the support tray 324, the system can include multiple elastic
elements and multiple masses configured in various forms. In these
configurations, the armature 322 is elastically coupled to the
support tray 324 as opposed to being rigidly attached to the
support tray 324. Configurations in which an armature is rigidly
attached to the support tray 324 are described herein.
[0075] The linear drive motor 308 can embody a moving coil or a
moving magnet-type linear motor. The linear drive motor 308 can
also include additional elements, such as a coil (not shown) and a
permanent magnet (not shown). The linear drive motor 308 can also
include a mechanism (not shown) for maintaining the armature 322 at
a predetermined position within the core before current is applied
to the coil of the linear drive motor 308. For example, the
mechanism can include a spring (not shown) that supports the mass
of the support tray 324, the target carrier 312, the specimen 311,
and any other moving elements, so that the linear drive motor 308
is not required to expend energy supporting a static load.
[0076] In one embodiment, the linear drive motor 308 can embody a
moving magnet-type linear motor of the type described in U.S. Pat.
No. 5,216,723, entitled "Permanent Magnet Transducing." The entire
disclosure of U.S. Pat. No. 5,216,723 is incorporated herein by
reference.
[0077] As previously described, a sensor 328 is rigidly coupled to
the support tray 324. The sensor 328 can be a position sensor, a
velocity sensor, an accelerometer, or a jerk sensor. The sensor 328
measures a parameter of the support tray 324 and generates an
electrical signal. The sensor 328 communicates the electrical
signal to the controller 306 through a signal transmission line
330.
[0078] An optional sensor (not shown) can be coupled between input
terminals (not shown) of the linear drive motor 308. The optional
sensor can be a load sensor that measures an impedance load of the
linear drive motor 308. The optional sensor can be configured to
send a signal indicative of the impedance load to the controller
306. The value of the impedance load can be related to the resonant
frequency of the moving elements of the system 300. Other sensors
for measuring electrical properties of the linear drive motor 308
can also be used.
[0079] An optional sensor 331 can be rigidly attached to the
armature 322. The sensor 331 can be a position sensor, a velocity
sensor, an accelerometer, or a jerk sensor. The sensor 331 measures
a parameter of the armature 322 and generates an electrical
armature signal. The sensor 331 communicates the electrical
armature signal to the controller 306 through a signal transmission
line 332. The controller 306 can use the electrical armature signal
to determine characteristics of the system 300. For example, the
electrical armature signal can be compared with the drive signal
from the current sensor 318 to determine performance
characteristics of the linear drive motor 308. The electrical
armature signal from the sensor 331 can also be used to determine
the resonance of the system 300. For example, the resonant
frequency of the system 300 corresponds to a frequency at which the
armature 322 has a minimum displacement.
[0080] The resonant shaker 300 can optionally include a probe 333
that can measure a property of the specimen 311. For example, the
property can include viscosity, mass, temperature, PH value,
resistivity, conductivity, etc. The probe 333 can be positioned so
as to be in contact with the specimen 311. In one embodiment, the
probe 333 can be a device that is designed to measure the
turbulence of a fluid, such as a pressure sensor. Alternatively,
the probe 333 can be a device that is designed to measure the
temperature of the specimen 311, such as a thermocouple. Examples
of probes for measuring the properties of specimens are described
in U.S. Pat. No. 5,033,321, entitled "Method and Apparatus for
Measuring the Degree of Mixing in a Turbulent Liquid System," the
entire disclosure of which is incorporated herein by reference.
[0081] The probe 333 communicates a probe signal to the analyzer
310 through a signal transmission line 334. The analyzer 310
analyzes the probe signal and generates an analyzer signal that is
transmitted to the controller 306 though a signal transmission line
336. The controller 306 processes the analyzer signal and
determines whether or not to continue processing or to adjust the
frequency and/or amplitude of the processing.
[0082] The resonant shaker 300 can also optionally include an
optical instrument 337, such as a spectrophotometer, a polarimeter,
or an ellipsometer, for example, that can measure a property of the
specimen 311 insitu. The optical instrument 337 can include an
emitter section 338 and a detector section 339. The optical
instrument 337 is coupled to the analyzer 310 through a signal
transmission line 340. Alternatively, the optical instrument 337 is
coupled to a different analyzer (not shown), a processor (not
shown), or to the controller 306.
[0083] The resonant shaker 300 can also include a keypad 341 that
can be mounted to the enclosure 302. The keypad 341 can include
control buttons 342 and/or rotary control knobs 344. The resonant
shaker 300 can also include a display 346, such as a liquid crystal
display (LCD) or a light emitting diode (LED) display. The display
346 can display system parameters, such as the shaking frequency,
elapsed time, information from the optical instrument 337, or other
parameters from the sensors 328, 331, and 333, for example. The
keypad 341 and/or the display 346 can be connected to the
controller 306 through a bi-directional signal line 348.
Alternatively, the keypad 341 and the display 346 can each be
connected to the controller 306 using two individual signal
transmission lines (not shown).
[0084] The resonant shaker 300 can also include one or more
input/output ports 350 for connecting the resonant shaker 300 to a
computer network, to another resonant shaker, or to external
equipment (not shown). For example, multiple resonant shakers 300
can be networked together and controlled by an external computer
(not shown) in order to facilitate batch processing.
[0085] The operation of the resonant shaker 300 is described with
reference to FIG. 4. FIG. 4 is a graphical representation 400 of
phase response as a function of frequency for the resonant shaker
of FIG. 3. The Y-axis 402 of FIG. 4 represents the absolute value
of the difference in phase between the electrical signal from the
sensor 328 (FIG. 3) and the drive signal from the current sensor
318 (FIG. 3). The X-axis 404 represents the frequency of
oscillation of the movable elements of the resonant shaker 300
including the specimen 311.
[0086] The frequency of the oscillation can be the resonant
frequency of the system 300. For example, the resonant frequency
provides thorough mixing of the specimen 311 while minimizing the
energy required to maintain the mixing. This assumes that the
linear drive motor 308 is not required to support the static mass
of the moving elements of the system 300 (e.g., the linear drive
motor can include suitably stiff armature centering springs). Thus,
it can be desirable to mix the specimen 311 at the resonant
frequency.
[0087] As previously described, the resonant frequency of the
system 300 is achieved by maintaining a predetermined phase
relationship between the drive signal and the electrical signal
from the sensor 328 (FIG. 3). If the sensor 328 is an
accelerometer, the predetermined phase relationship is
ninety-degrees. If the sensor 328 is a velocity sensor, the
predetermined phase relationship is zero-degrees. If the sensor 328
is a position sensor, the predetermined phase relationship is
ninety-degrees.
[0088] In another example, the frequency of the oscillation can be
off resonance. In this example, the control algorithm drives the
system below the resonant frequency. The control algorithm can also
drive the system above the resonant frequency. In one embodiment,
the control algorithm can use this information to determine that
the resonant frequency does indeed exist.
[0089] Additionally, the controller 306 can also adjust the
amplitude of the oscillation during the processing of the specimen
311 by supplying an appropriate amplitude of drive current to the
linear drive motor 308. The linear drive motor 308 can drive the
support tray 324 to various different vertical displacements during
the operation of the resonant shaker 300. The amplitude of the
vertical displacement depends on the specimen 311 and the desired
mixing parameters. The maximum amplitude adjustment is related to
the maximum excursion of the armature 322 of the linear drive motor
308.
[0090] As shown in FIG. 4, the phase response has a substantially
monotonic behavior over an illustrative frequency range of
interest. The desired ninety-degree phase value is located in the
substantially linear range between approximately 45 Hz and
approximately 55 Hz. The resonant frequency can change as mass is
added to the system. For example, if the system 300 is operated
without a target carrier containing a specimen 311, the resonant
frequency can be approximately 60 Hz. When a target carrier
containing a typical specimen 311 is added to the support tray 324,
the resonant frequency can decrease to 50 Hz, for example. The
resonant frequency decreases further as additional mass is added to
the support tray 324.
[0091] Thus, when the frequency of the drive control signal is
constrained to only operate in the vicinity of the desired resonant
frequency, substantially above lower parasitic system resonances
but substantially below higher parasitic resonances, the phase
relationship follows the substantially monotonic curve 406 shown in
FIG. 4.
[0092] Toward the low frequency end 408 of the curve 406 (35 Hz in
this example), the slope of the curve 406 is approximately zero. As
the frequency increases, the slope of the curve 406 transitions
such that the slope reaches a maximum value. The sharpness of this
transition is directly related to the Q of the mechanical system.
The curve 406 is substantially linear between approximately 45 Hz
and approximately 55 Hz. At the higher frequency range 410, the
slope of the curve 406 transitions to approximately zero.
[0093] The controller 306 (FIG. 3) attempts to adjust the frequency
of the drive control signal to operate on the center of the curve
406 in the linear region where the phase of the relationship
between the acceleration signal and the drive signal is
ninety-degrees. As previously described, the frequency depends on
the mass of the moving elements of the system 300. Since the
response is non-linear, the controller 306 implements a hunting
algorithm to locate the desired operating point at the center of
the curve 406. The details of the hunting algorithm are described
in detail herein. Other techniques and algorithms that are not
described can also be used to locate the desired operating point at
the center of the curve 406. Although a monotonic phase
relationship is illustrated, other types of phase curves, linear or
non-linear, can also be used. Additionally, the phase relationship
can also be different than ninety-degrees.
[0094] The controller 306 (FIG. 3) determines the frequency of the
drive control signal as follows. The controller 306 first drives
the system at the lower frequency bound (35 Hz) and then waits long
enough for the phase measurement to stabilize (this wait time is
proportional to the Q of the system). The controller 306 then
determines whether the phase measurement is below the desired
operating point of ninety-degrees. Alternatively, the set point can
be different than ninety-degrees. If the controller 306 determines
that the phase measurement is not below the desired set point
(ninety-degrees), the controller 306 can generate a fault
condition, such as the specimen 311 is too heavy for the system
300.
[0095] If the controller 306 determines that the phase measurement
is below the desired set point (ninety-degrees), the controller 306
changes the drive frequency to the upper frequency bound (65 Hz).
The controller 306 again waits for the phase measurement to
stabilize and determines whether the phase measurement is above the
desired set point of ninety-degrees. If the controller 306
determines that the phase measurement is not above the desired set
point (ninety-degrees), the controller 306 can generate a fault
condition, such as a sensor fault.
[0096] If the controller 306 determines that the phase measurement
is above the desired set point (ninety-degrees), the controller 306
determines that the desired set point is bracketed. The controller
306 then estimates the next frequency by choosing midpoint of the
upper and the lower frequencies last used. The controller 306 then
determines whether this next frequency is above or below the
desired phase set point, and then chooses another frequency by
bisecting the most recent frequency bracket. Once the controller
306 creates a frequency bracket (around the desired set point) that
has a width that is less than or equal to a predetermined threshold
that is related to the resolution of the controller 306, it
modifies the hunting strategy. In one embodiment, the controller
306 enters a variable stepping mode scheme.
[0097] The variable stepping mode adjusts the frequency in the
direction of the desired phase using a step size that is determined
by the magnitude of the phase error. In one embodiment, the phase
error is calculated as the difference in the output of the phase
detector in the controller 306 and ninety-degrees. The sign of the
phase error determines the direction of the correction. As the
control scheme gets closer to the desired set point, the step size
is reduced and the control scheme dithers around the desired set
point. If the system is disturbed, the controller 306 adjusts the
step size and effectively re-hunts for the set point. Since the
controller can be a digital controller having a finite step size,
the exact resonance match may not be achieved. However, the system
can be driven into resonance by dithering around the set point. The
controller 306 can also adjust the amplitude of the resonance by
supplying an appropriate amplitude of the drive current to the
linear drive motor 308. The appropriate amplitude of drive current
can reduce or intensify the displacement of the resonant
oscillation.
[0098] FIG. 5 illustrates a block diagram of another resonant
shaker 500 according to the invention. The resonant shaker 500 is
similar to the resonant shaker 300 of FIG. 3 and includes an
enclosure 502 that houses the power supply 304, a controller 503
and a linear drive motor 504. The linear drive motor 504 can have
different characteristics than the linear drive motor 308 of FIG.
3. For example, the linear drive motor 504 can require less output
power than the linear drive motor 308 and can have larger
displacement requirements. Additionally, the linear drive motor 504
does not require centering springs since the static mass of the
moving elements is supported by elastic elements 505 and not by the
linear drive motor 504 in this embodiment.
[0099] The enclosure 502 can also include the feet 309. The feet
309 can be composed of an elastic material, such as rubber, to
dampen vibrations from the resonant shaker 500 and to prevent the
resonant shaker 500 from moving in a lateral direction during
operation. Other suitable materials can also be used to reduce
vibration and/or prevent the resonant shaker 500 from moving during
operation. The resonant shaker 500 can also include the optional
analyzer 310 that can analyze certain properties of a specimen 311.
The resonant shaker 500 is generally placed on a solid surface 312
such as a table, a pedestal, a floor, or a shelf. The power supply
304 is configured to supply power to the controller 503, the
analyzer 310, and any other necessary and/or optional
components.
[0100] The controller 503 couples power to the linear drive motor
504 through the power transmission line 316. The current sensor 318
is coupled to the power transmission line 316 and measures the
drive current supplied to the linear drive motor 504. The current
sensor 318 communicates a drive signal to the controller 503.
[0101] The linear drive motor 504 includes an armature 506 that is
coupled to a support tray 507 through a rigid coupling 508. The
support tray 507 is coupled to a frame 510 of the enclosure 502
through one or more of the elastic elements 505. Alternatively, the
elastic elements 505 can couple the support tray 507 to the base of
the resonant shaker 500 or the solid surface 312. Any configuration
that locates the one or more elastic elements 505 in a parallel
arrangement with the armature 506 can be used. For example, the
system can include multiple elastic elements, such as springs
between the support tray 507 and the frame 510.
[0102] The elastic element 505 can include, but is not limited to,
a coil spring, a leaf spring, a torsional spring, a disk spring, an
elliptic spring, a helical spring, an air spring, a cantilever
spring, a rubber element, such as a grommet, or any element that
stores energy as a function of displacement and when released,
eventually recovers its basic form and position.
[0103] The linear drive motor 504 can embody a moving coil or a
moving magnet-type linear motor. The linear drive motor 504 can
also include additional elements, such as a coil (not shown) and a
permanent magnet (not shown).
[0104] As previously described, a sensor 328 is rigidly coupled to
the support tray 507. The sensor 328 can be a position sensor, a
velocity sensor, an accelerometer, or a jerk sensor. The sensor 328
measures a parameter of the support tray 507 and generates an
electrical signal that is transmitted to the controller 503.
[0105] The resonant shaker 500 can optionally include the probe 332
that can measure a property of the specimen 311. For example, the
property can include viscosity, mass, temperature, PH value,
resistivity, conductivity, etc. The probe 332 can be positioned so
as to be in contact with the specimen 311.
[0106] The probe 332 communicates a probe signal to the analyzer
310. The analyzer 310 analyzes the probe signal and generates an
analyzer signal that is transmitted to the controller 503. The
controller 503 processes the analyzer signal and determines whether
or not to continue processing or to adjust the frequency and/or
amplitude of the shaking.
[0107] The resonant shaker 500 can also include a keypad 341 that
can be mounted to the enclosure 502. The resonant shaker 500 can
also include a display 346, such as a liquid crystal display (LCD)
or a light emitting diode (LED) display. The display 346 can
display system parameters, such as the shaking frequency, elapsed
time, or other parameters from the sensor 332, for example. The
keypad 341 and/or the display 346 can be connected to the
controller 503 as previously described.
[0108] The resonant shaker 500 can also include one or more
input/output ports 350 for connecting the resonant shaker 500 to a
computer network, to another resonant shaker, or to external
equipment (not shown). For example, multiple resonant shakers 500
can be networked together and controlled by an external computer
(not shown) in order to facilitate batch processing.
[0109] The operation of the resonant shaker 500 is described with
reference to FIG. 6. FIG. 6 is a graphical representation 600 of
phase response as a function of frequency for the resonant shaker
500 of FIG. 5.
[0110] The Y-axis 602 of FIG. 6 represents the absolute value of
the difference in phase between the electrical signal from the
sensor 328 (FIG. 5) and the drive signal from the current sensor
318 (FIG. 5). The X-axis 604 represents the frequency of
oscillation of the movable elements of the resonant shaker 500
including the specimen 311.
[0111] The frequency of the oscillation can be the resonant
frequency of the system 500. The resonant frequency provides
efficient shaking of the specimen 311 while minimizing the energy
required to maintain the shaking. Thus, it can be desirable to
shake the specimen 311 at the resonant frequency.
[0112] As previously described, the resonant frequency of the
system 500 is achieved by maintaining a predetermined phase
relationship between the drive signal from the current sensor 318
and the electrical signal from the sensor 328 (FIG. 5). If the
sensor 328 is an accelerometer, the predetermined phase
relationship is zero-degrees or 180-degrees for the resonant shaker
500 of FIG. 5. Thus, the phase relationship is different for the
system 500 of FIG. 5 as compared to the system 300 of FIG. 3. This
is due to the differences in the configurations of the resonant
shaker 300 and the resonant shaker 500. Referring back to FIG. 5,
if the sensor 328 is a velocity sensor, the predetermined phase
relationship is ninety-degrees. If the sensor 328 is a position
sensor, the predetermined phase relationship is zero or
180-degrees.
[0113] As previously described, the controller 503 can also adjust
the amplitude of the oscillation during the processing of the
specimen 311. The linear drive motor 504 can displace the support
tray 324 to various different vertical positions depending on the
specimen and the desired mixing parameters. The maximum amplitude
adjustment is related to the maximum excursion of the armature 505
of the linear drive motor 504 and the amplitude of the drive
current.
[0114] As shown in FIG. 6, the phase response has a substantially
monotonic behavior over an illustrative frequency range of
interest. The desired zero or 180-degree phase value is located in
the substantially linear range between approximately 45 Hz and
approximately 55 Hz.
[0115] Thus, when the frequency of the drive control signal is
constrained to only operate in the vicinity of the desired resonant
frequency, substantially above lower parasitic system resonances
but substantially below higher parasitic resonances, the phase
relationship follows the substantially monotonic curve 606 shown in
FIG. 6.
[0116] Toward the low frequency end 608 of the curve 606 (35 Hz in
this example), the slope of the curve 606 is approximately zero. As
the frequency increases, the slope of the curve 606 transitions to
such that the slope reaches a maximum. The sharpness of this
transition is directly related to the Q of the mechanical system.
The curve 606 remains substantially linear between approximately 45
Hz and approximately 55 Hz. At the higher frequency range 610, the
slope of the curve 606 transitions to approximately zero.
[0117] The controller 503 (FIG. 5) adjusts the frequency of the
drive control signal to operate on the center of the curve 606 in
the linear region where the phase of the relationship between the
acceleration signal and the drive signal is zero-degrees. As
previously described, the frequency depends on the mass of the
moving elements of the system. Since the response is non-linear,
the controller 503 implements a hunting algorithm to locate the
desired operating point at the center of the curve 606. The details
of the hunting algorithm are described in detail with reference to
FIG. 4. Other techniques and algorithms that are not described can
also be used to locate the desired operating point at the center of
the curve 606. Although a monotonic phase relationship is
illustrated, other types of phase curves, linear or non-linear, can
also be used. Additionally, the phase relationship can also be
different than zero-degrees.
[0118] While the invention has been particularly shown and
described with reference to specific preferred embodiments, it
should be understood by those skilled in the art that various
changes in form and detail may be made therein without departing
from the spirit and scope of the invention as defined herein. For
example, although the systems and techniques are described
primarily in the context of shaking at resonant frequencies, the
systems and techniques are also applicable to shaking at other
desired frequencies. In addition, although certain examples of
control techniques and feedback mechanisms are described, the
systems and techniques may be used in connection with other control
techniques and feedback mechanisms. Accordingly, other embodiments
are within the scope of the following claims.
* * * * *