Title: Rotor speed control device and method
Abstract: Kinetic energy of a rotor is substantially prevented from exceeding a predetermined amount of kinetic energy by determining a first kinetic energy of the rotor spinning at a first rotational velocity and determining whether the first kinetic energy exceeds the predetermined amount of kinetic energy. In addition, torque being applied to the rotor is modulated in response to the first kinetic energy exceeding the predetermined amount of kinetic energy. In this manner, the rotor is spun at a relatively slower rotational velocity than the first rotational velocity.
Patent Number: 6,943,509 Issued on 09/13/2005 to Schneider, et al.
| Inventors:
|
Schneider; Harvey (Southbury, CT);
Carson; David Michael (Newtown, CT)
|
| Assignee:
|
Kendro Laboratory Products, LP (Newton, CT)
|
| Appl. No.:
|
615295 |
| Filed:
|
July 9, 2003 |
| Current U.S. Class: |
318/268; 73/865.9; 318/432; 318/434; 494/7; 494/8 |
| Intern'l Class: |
H02P 005/00 |
| Field of Search: |
318/375,432,433,434,729,759,472,700
494/7-12,37
700/273,275
388/809,811,844
702/41,132
73/137,865.9
|
References Cited [Referenced By]
U.S. Patent Documents
| 4700117 | Oct., 1987 | Giebeler et al.
| |
| 4827197 | May., 1989 | Giebeler.
| |
| 4903191 | Feb., 1990 | Fries.
| |
| 5235864 | Aug., 1993 | Rosselli et al.
| |
| 5431620 | Jul., 1995 | Schenck et al.
| |
| 5467001 | Nov., 1995 | Iwashita.
| |
| 5509881 | Apr., 1996 | Sharples.
| |
| 5600076 | Feb., 1997 | Fleming et al.
| |
| 5650578 | Jul., 1997 | Fleming et al.
| |
| 5800331 | Sep., 1998 | Song.
| |
| 5837879 | Nov., 1998 | Zick.
| |
| 6204627 | Mar., 2001 | Watanabe et al.
| |
| 6205405 | Mar., 2001 | Pouvreau.
| |
| 6368265 | Apr., 2002 | Barkus et al.
| |
| 6679820 | Jan., 2004 | Barkus et al.
| |
| 6747427 | Jun., 2004 | Carson.
| |
| 2004/0033878 | Feb., 2004 | Carson et al.
| |
Primary Examiner: Ip; Paul
Attorney, Agent or Firm: Baker & Hostetler LLP
Claims
1. A system for controlling rotational speed of a rotor within a centrifuge,
the system comprising:
a motor operative to rotate the rotor;
a modulation controller configured to modulate an amount of torque generated
by the motor and thereby modulate the rotational speed of the rotor;
a speed sensor configured to sense the rotational speed of at least one of the
motor and the rotor, and transmit the sensed rotational speed to the controller;
and
wherein the controller is configured to determine an amount of kinetic energy
associated with the rotor in response to the amount of torque and the sensed rotational
speed, and is configured to compare the amount of kinetic energy associated with
the rotor to a predetermined amount of kinetic energy, the controller being further
configured to reduce the rotational speed of the motor in response to the compared
amount of kinetic energy associated with the rotor being greater than the predetermined
amount of kinetic energy.
2. The system according to claim 1, further comprising a torque sensor configured
to sense the amount torque generated by the motor and transmit the sensed torque
to the controller.
3. The system according to claim 1, wherein the controller is further configured
to calculate the amount of torque applied to rotor by the motor in response to
a predetermined motor torque characteristic and a measured amount of current applied
to the motor.
4. The system according to claim 1, wherein the controller is further configured
to compare the amount of kinetic energy associated with the rotor to the predetermined
amount of kinetic energy while the rotor is spinning at a relatively slow speed,
the relatively slow speed being below a speed sufficient to impart an amount of
kinetic energy that is greater than the predetermined amount of kinetic energy.
5. The system according to claim 1, further comprising a timer configured to
count a time increment and transmit the time increment to the controller, wherein
the controller is further configured to determine an acceleration rate of the rotor
based on a change in rotational speed during the time increment.
6. The system according to claim 5, wherein the controller is further configured
to determine a deceleration rate in response to a change in rotational speed during
an idle state of the motor for the time increment.
7. The system according to claim 1, wherein the controller is further configured
to determine the amount of kinetic energy of the rotor at a relative maximum speed
of the rotor during a run, the controller being further configured to compare the
amount of kinetic energy of the rotor at the relative maximum speed to the predetermined
amount of kinetic energy and the controller being configured to substantially prevent
the rotor from obtaining the relative maximum speed in response to the amount of
kinetic energy of the rotor at the relative maximum speed being relatively larger
than the predetermined amount of kinetic energy.
8. An apparatus for substantially preventing kinetic energy of a rotor from exceeding
a predetermined amount of kinetic energy, the apparatus comprising;
means for determining a first kinetic energy of the rotor spinning at a first
rotational velocity;
means for determining whether the first kinetic energy exceeds the predetermined
amount of kinetic energy; and
means for modulating torque being applied to the rotor in response to the first
kinetic energy exceeding the predetermined amount of kinetic energy, wherein the
rotor is spun at a relatively slower rotational velocity than the first rotational
velocity.
9. The apparatus according to claim 8, further comprising means for determining
an acceleration rate of the rotor.
10. The apparatus according to claim 9, further comprising means for determining
a deceleration rate of the rotor, wherein the first kinetic energy is determined
based on the deceleration rate, the acceleration rate, the first rotational velocity
and the torque being applied to the rotor.
11. The apparatus according to claim 8, further comprising means for determining
the first kinetic energy prior to the rotor spinning at the first rotational velocity.
12. A method of substantially preventing kinetic energy of a rotor from exceeding
a predetermined amount of kinetic energy, the method comprising;
determining a first kinetic energy of the rotor spinning at a first rotational
velocity;
determining whether the first kinetic energy exceeds the predetermined amount
of kinetic energy; and
modulating torque applied to the rotor in response to the first kinetic energy
exceeding the predetermined amount of kinetic energy wherein, the rotor is spun
at a relatively slower rotational velocity than the first rotational velocity.
13. The method according to claim 12, further comprising determining an acceleration
rate of the rotor.
14. The method according to claim 13, further comprising determining a deceleration
rate of the rotor, wherein the first kinetic energy is determined based on the
deceleration rate, the acceleration rate, the first rotational velocity and the
torque being applied to the rotor.
15. The method according to claim 12, further comprising determining the first
kinetic energy prior to the rotor spinning at the first rotational velocity.
Description
FIELD OF THE INVENTION
The present invention generally relates to a rotor speed controlling device and
method. More particularly, the present invention pertains to a device and method
of controlling rotor speed as a result of applied torque inconsistencies.
BACKGROUND OF THE INVENTION
It is generally known that centrifuges are employed to apply centripetal force
on to samples and thereby precipitate, separate or fractionate constituents within
the samples. Within the centrifuge, a rotor is generally configured to contain
the sample. The rotor is typically spun by a motor. That is, the motor applies
torque in a direction that is perpendicular to the axis of the rotor to modulate
the rotational velocity or speed of the rotor and thereby generate centripetal
force. In addition to the generation of centripetal force, the torque applied to
the rotor is converted into kinetic energy as the inertial mass of the rotor gains speed.
In the event of a failure of the rotor, the kinetic energy may cause undesirable
consequences to personnel and/or property in the vicinity. Therefore, centrifuges
typically include a containment system configured to contain and/or dissipate eject
a having a certain amount of energy. However, due to the fact that the kinetic
energy of the rotor increases as a factor of the rotational velocity squared, it
may be undesirably expensive to produce a containment system capable of containing
all conceivable amounts of energy a failed rotor may impart.
To facilitate the prevention of a failure of the rotor, rotors typically include
a maximum rated speed corresponding to a theoretical and/or empirically derived
maximum safe operating speed of the rotor. In addition, there are various conventional
rotor identification protocols configured to substantially prevent rotors from
being spun at a rate greater than their corresponding maximum rated speed. However,
there is not currently a system configured to prevent the kinetic energy of a rotor
from exceeding an amount of kinetic energy that the containment system is configured
to contain.
Accordingly, it is desirable to provide a method and apparatus capable
of overcoming the disadvantages described herein at least to some extent.
SUMMARY OF THE INVENTION
The foregoing needs are met, to a great extent, by the present invention, wherein
in one respect an apparatus and method is provided that in some embodiments substantially
prevents an amount of kinetic energy of a rotor spinning in a centrifuge from exceeding
a predetermined amount of kinetic energy.
An embodiment of the present invention pertains to an apparatus for controlling
rotational speed of a motor operable to apply torque to a rotor within a centrifuge
configured to contain a predetermined amount of kinetic energy (KE
pred)
resulting from a failure of the rotor. In this apparatus, an acceleration rate
and a deceleration rate of the rotor is determined by a processor. This processor
is further configured to determine an amount of kinetic energy of the rotor at
a set rotational speed (KE
ss) in response to the acceleration rate and
the deceleration rate and the processor is further again configured to compare
the KE
ss to the KE
pred. In this manner, the processor is
configured to substantially prevent the rotor from obtaining the set rotational
speed in response to the KE
ss exceeding the KE
pred.
Another embodiment of the present invention relates to a system for controlling
rotational speed of a rotor within a centrifuge. This system includes a motor,
controller, and speed sensor. The motor is operative to rotate the rotor. The controller
is configured to modulate an amount of torque generated by the motor and thereby
modulate the rotational speed of the rotor. The speed sensor is configured to sense
the rotational speed of at least one of the motor and the rotor, and transmit the
sensed rotational speed to the controller. In this regard, the controller is configured
to determine an amount of kinetic energy associated with the rotor in response
to the amount of torque and the sensed rotational speed. The controller is further
configured to compare the amount of kinetic energy associated with the rotor to
a predetermined amount of kinetic energy. Moreover, the controller is configured
to reduce the rotational speed of the motor in response to the compared amount
of kinetic energy associated with the rotor being greater than the predetermined
amount of kinetic energy.
Yet another embodiment of the present invention pertains to an apparatus for
substantially preventing kinetic energy of a rotor from exceeding a predetermined
amount of kinetic energy. This apparatus includes a means for determining a first
kinetic energy of the rotor spinning at a first rotational velocity, a means for
determining whether the first kinetic energy exceeds the predetermined amount of
kinetic energy, and a means for modulating torque being applied to the rotor in
response to the first kinetic energy exceeding the predetermined amount of kinetic
energy. In this manner, the rotor is spun at a relatively slower rotational velocity
than the first rotational velocity.
Yet another embodiment of the present invention relates to a method of substantially
preventing kinetic energy of a rotor from exceeding a predetermined amount of kinetic
energy. In this method, a first kinetic energy of the rotor spinning at a first
rotational velocity is determined and it is determined whether the first kinetic
energy exceeds the predetermined amount of kinetic energy. Torque being applied
to the rotor is modulated in response to the first kinetic energy exceeding the
predetermined amount of kinetic energy. In this manner, the rotor is spun at a
relatively slower rotational velocity than the first rotational velocity.
There has thus been outlined, rather broadly, certain embodiments of the invention
in order that the detailed description thereof herein may be better understood,
and in order that the present contribution to the art may be better appreciated.
There are, of course, additional embodiments of the invention that will be described
below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in
detail, it is to be understood that the invention is not limited in its application
to the details of construction and to the arrangements of the components set forth
in the following description or illustrated in the drawings. The invention is capable
of embodiments in addition to those described and of being practiced and carried
out in various ways. Also, it is to be understood that the phraseology and terminology
employed herein, as well as the abstract, are for the purpose of description and
should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which
this disclosure is based may readily be utilized as a basis for the designing of
other structures, methods and systems for carrying out the several purposes of
the present invention. It is important, therefore, that the claims be regarded
as including such equivalent constructions insofar as they do not depart from the
spirit and scope of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a centrifuge device according to an embodiment
of the invention.
FIG. 2 is a block diagram of a controller for the centrifuge device of FIG. 1.
FIG. 3 is a flow diagram illustrating steps that may be followed in accordance
with an embodiment of the method or process.
FIG. 4 is a flow diagram illustrating steps that may be followed in accordance
with an embodiment of the method or process.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
At least some embodiments of the present invention provide an apparatus that
is
configured to substantially prevent an amount of kinetic energy of a rotor spinning
in a centrifuge from exceeding a predetermined amount of kinetic energy. Other
embodiments in accordance with the present invention provide a method of substantially
preventing an amount of kinetic energy of a rotor spinning in a centrifuge from
exceeding a predetermined amount of kinetic energy. At least one advantage that
various embodiments of the invention include is essentially preventing the kinetic
energy of a rotor spinning in a centrifuge from exceeding an amount of kinetic
energy the centrifuge is configured to contain. In this manner, the various embodiments
of the invention are configured to reduce the likelihood of undesirable consequences
occurring as a result of a failure of the rotor.
The invention will now be described with reference to the drawing figures, in
which like reference numerals refer to like parts throughout. As shown in FIG.
1, a centrifuge
10 is configured to control the rotational velocity of a
rotor
12. To impart torque in a direction perpendicular to the axis of rotation
for the rotor
12, the centrifuge
10 includes a motor
14, drive
electronics
16 and a controller
18. The motor
14 is modulated
by the drive electronics
16 based upon signals received from the controller
18. For example, in response to pulse width modulation (PWM) and/or modulation
of current being applied to the motor
14, the amount of torque generated
by the motor
14 may be controlled. This torque may be applied to the rotor
12 from the motor
14 via any suitable manner such as, a drive shaft,
coupling, linkage, gyro shaft, drive cone, and the like. To determine the amount
of torque applied, the centrifuge
10 may include a torque sensor
20
configured to sense torque generated by the motor
14 and transmit measurements
associated with this generated torque to the controller
18. For example,
the torque sensor may include a magnetostrictive sensor configured to sense changes
in magnetic permeability and/or lines of magnetic flux. Measurements associated
with these sensed permeability and/or flux line changes may be relayed by the torque
sensor
20 to the controller
18. However, it is within the scope of
embodiments of the invention that the torque sensor
20 be subsumed within
the motor
14. For example, the motor
14 may include a switched reluctance
motor configured to forward measurements associated with generated toque to the
controller
18. In additional, it is within the scope of various embodiments
of the invention that the amount of torque applied may be determined in a variety
of other manners. For example, the applied torque may be calculated based on a
measured input current and predetermined motor torque characteristics. These predetermined
motor torque characteristics may be derived empirically, provided by the manufacturer,
etc. Furthermore, other examples of suitable motors include induction, brushless
DC, and the like.
The drive electronics
16 are configured to modulate the motor
14
in response to signals from the controller
18. For example, the drive electronics
may output PWM and/or current to the motor
14 in response to signals received
from the controller
18. In this regard, the controller
18 is configured
to determine and transmit these signals in response rotational velocity measurements
and run parameters. The rotational velocity measurements may be sensed by a speed
sensor
22. The speed sensor
22 may be configured to sense a rotational
velocity or angular velocity associated with the rotor
12. For example,
the speed sensor
22 may include a tachometer configured to directly sense
the angular velocity of the drive shaft or various other components of the motor
14 and/or drive train. This sensed angular velocity may correlate to the
angular velocity of the motor
14. However, it is within the scope of various
embodiments of the invention that the speed sensor
22 is configured to directly
sense the angular velocity of the rotor
14. With regard to the run parameters,
these parameters may include run duration, set speed, set temperature, ramp up
rate, ramp down rate, and the like. The run parameters may be entered via a control
interface
24 by a user for example. The control interface
24 may
include a user interface operable to receive inputs from the user.
In a typical run, the rotor
12 is accelerated to the set speed, maintained
at the set speed for the run duration and decelerated until essentially stopped.
During acceleration to the set speed, the rotor
12 gains kinetic energy
(KE
rotor) as a function of the mass inertia multiplied by the angular
velocity squared. A particular example of a suitable equation for determining the
KE
rotor may include:
##EQU1##
Where: KE
rotor is the kinetic energy in foot pounds (ft-lbs) at
speed equals S in radians per second (rad/sec) for a rotor having an inertia mass
of I
r in inch pounds per second squared (in-lbs-sec
2).
In the event of a failure of the rotor
12, this accumulated KE
rotor
will drive the rotor
12, or pieces of the rotor
12 outward from the
axis of rotation with possible undesirable consequences. In this regard, the centrifuge
10 includes a containment system
26. This containment system
26
is configured to contain and/or dissipate a predetermined amount of kinetic energy
(KE
con). For example, the containment system
26 may include a
tub having 2 cm steel sides, 6 cm steel bottom, and a 1.25 cm steel lid. In this
manner, the containment system
26 may facilitate containing at least the
KE
con. The KE
con may be determined based on a plurality of
factors such as, type or types of rotors available for the centrifuge
10,
manufacturers specifications, empirical data, maximum speed and/or torque of the
motor
14, and the like. According to an embodiment of the invention and
as described herein, the centrifuge
10 is configured to substantially prevent
the KE
rotor from exceeding the KE
con.
FIG. 2 is a block diagram of the controller
18. As shown in FIG. 2, the
controller
18 includes a processor
28, analog to digital (A/D) converter
30, input/output (I/O) port
32, clock
34, and memory
36.
The I/O port
32 is configured to receive signals from any suitably attached
electronic device and forward these signals to the A/D converter
30 and/or
the processor
28. For example, the I/O port
32 may receive signals
associated with torque generated by the motor
14 and forward the signals
to the processor
28. If the signals are in analog format, the signals may
proceed via the A/D converter
30. In this regard, the A/D converter
30
is configured to receive analog format signals and convert these signals into corresponding
digital format signals. Conversely, the A/D converter
30 is configured to
receive digital format signals from the processor
28, convert these signals
to analog format, and forward the analog signals to the I/O port
32. In
this manner, electronic devices configured to receive analog signals may intercommunicate
with the processor
28.
The processor
28 is configured to receive and transmit signals to and
from the A/D converter
30 and/or the I/O port
32. The processor
28
is further configured to receive time signals from the clock
34. In addition,
the processor
28 is configured to store and retrieve electronic data to
and from the memory
36. Furthermore, the processor
28 is configured
to determine signals operable to modulate the motor
14 and thereby control
the rotor
12 to rotate at a particular rate. For example, signals associated
with the speed of the rotor
12 may be forwarded by the speed sensor
22
and received by the processor
28. Based on the speed of the rotor
12,
the processor
28 may determine modulations to pulse width signal that will
facilitate the rotor
12 spinning at a particular rate, for example. Moreover,
the processor
28 is configured to determine an acceleration rate for the
rotor
14 (R
a) and deceleration rate for the rotor
14 (R
d).
For example, while the motor
14 is applying sufficient torque to the rotor
12 to cause acceleration of the rotor
12, the acceleration rate of
the rotor
12 may be determined by sensing a first speed of the rotor
12,
waiting an increment of time, and sensing a second speed of the rotor
12.
The difference between the first and the second speed of the rotor
12 divided
by the increment of time may be determined to be the acceleration rate. Similarly,
while the rotor
12 is spinning and the motor
14 is in an idle state,
the deceleration rate of the rotor
12 may be determined by sensing a first
speed of the rotor
12, waiting an increment of time, and sensing a second
speed of the rotor
12. The difference between the first and the second speed
of the rotor
12 divided by the increment of time may be determined to be
the deceleration rate.
According to an embodiment of the invention, the processor
28 is
configured to substantially prevent the KE
rotor from exceeding KE
con.
Generally, the greatest rotational velocity (speed) achieved by the rotor
12
during the run is essentially equal to the set speed. Consequently, the greatest
KE
rotor during the run typically occurs at the set speed. In this regard,
the processor
28 is configured to determine the KE
rotor at the
set speed (KE
ss). If the KE
ss is determined to exceed the
KE
con, the processor
28 is configured to substantially prevent
the rotor
12 from obtaining the set speed. For example, the processor
28
may reduce the set speed or stop the run. While a variety of suitable equations
may be utilized to determine the KE
ss, a particular example of a suitable
equation includes:
##EQU2##
Where: T
a is the torque applied by the motor
14; I
d
is the inertia of the drive train including some or all of the motor rotor,
coupling, gyro shaft and drive cone; R
a is the acceleration rate of
the rotor
12; R
d is the deceleration rate of the rotor
12;
and S
s is the set speed.
With regard to the I
d, this value may be empirically determined and
stored to the memory
36, for example. With regard to the T
a,
this value may be expressed in a variety of suitable manners such as total energy
applied to the motor
14, inch pounds, and/or torque per applied amperage
of current. In addition, the T
a may be determined utilizing a variety
of suitable equations such as:
##EQU3##
Where: Ke is an empirically determined amount of torque per applied ampere
of current, Ca is the applied current, and PWM is the pulse width modulation.
FIG. 3 is a flow diagram illustrating steps that may be followed in accordance
with an embodiment of a method
40. Prior to initiation of the method
40,
a great variety of pre-run steps may occur. These pre-run steps include, in no
particular order: the centrifuge
10 may be turned on, run parameters may
be entered, a set temperature may be achieved, the rotor
12 may be placed
in the centrifuge
10, the containment system
26 may be secured, a
set atmospheric pressure within the containment system may be achieved, a system
check may be performed, and a start run command may be received. Following the
pre-run steps, the run may be initiated at step
42.
At step
44, the speed of the rotor
12 (S
rotor) is sensed.
For example, the speed sensor
22 may sense the rotational velocity of the
motor
14, a drive shaft of the motor
14, the rotor
12, or
the like. In this regard, as the rotor
12 is configured for attachment to
the motor
14 via the drive train of the motor
14, it is within the
scope of embodiments of the invention that the S
rotor may be indirectly
determined based on the rotational velocity of one or more components of the drive
train of the motor
14. In addition, as the S
rotor may be calculated
based on signals utilized to control the motor
14, it is to be understood
that the S
rotor may be determined based on a calculated speed of the
motor
14.
At step
46, the S
rotor is modulated. For example, in response
to receiving measurements associated with the S
rotor, the controller
18 may determine the S
rotor. In addition, the controller
18
may, in response to determining the S
rotor, determine signals associated
with PWM and/or applied current and forward these signals to the drive electronics
16. The drive electronics
16 may, in turn, provide power to the motor
14 according to these signals. In this, or any other suitable manner, the
S
rotor may be modulated.
At step
48, it is determined if the rotor
12 has achieved the set
speed (S
s). For example, the S
rotor sensed at step
44
may be compared to the S
s. If the S
rotor is essentially equal
to or greater than the S
s, the run may be performed at step
50.
If the S
rotor is less than the S
s, it is determined, at step
54, if a check has been performed.
At step
50, the S
rotor may be maintained at the S
s for
the duration of the run. Following the duration of the run, the rotor
12
may be allowed to slow and/or a breaking force in the form of torque opposite to
the direction of rotation may be applied to the rotor
12 until the rotor
12 has essentially stopped rotating. Following the step
50, the centrifuge
10 may idle at step
52 until additional commands are received.
At step
54, it is determined whether the check has been performed. In
this
check, it is determined if the rotor
12 has achieved a check speed (S
check).
With regard to the S
check, in order to facilitate preventing the KE
rotor
from exceeding the KE
con the S
rotor is determined at a speed
at which essentially no rotor configured to function in the centrifuge would have
acquired a KE
rotor greater than the KE
con. Therefore, the
S
check may be determined to be any reasonable value from approximately
zero revolutions per minute (rpm) to about the speed at which a rotor having a
comparatively high inertia mass and configured to function in the centrifuge
10
would exceed the KE
con. To continue with the description of step
54,
if the check has been performed, the S
rotor may be sensed at step
44.
If the check has not been performed, it may be determined at step
56 if
the S
rotor has achieved the S
check.
At step
56, it is determined whether the S
rotor has achieved
the S
check. For example, the S
rotor may be compared to the
S
check. If the S
rotor is essentially equal to or greater
than the S
check, the check may be initiated at step
58. If the
S
rotor is less than the S
check, the S
rotor may
be sensed again at step
44.
At step
58, the check is initiated. In an embodiment of the invention
the
check includes comparing the KE
ss to the KE
con. The KE
con
is determined empirically and/or based upon the configuration of the containment
system
26. The KE
con may be stored to the memory
36 for
access by the processor
28. The KE
ss may be determined in any
suitable manner. In a specific example, the KE
ss may be determined utilizing
Eqn. 2 and the T
a, the I
d, the R
a, the R
d,
and the S
s as illustrated herein.
At step
60, it is determined whether an error has been detected. For example,
if it is determined, at step
58, that the KE
ss is greater than
the KE
con, an error mode may be initiated at step
62. If an error
is not detected, the S
s may be sensed at step
44.
According to various embodiments of the invention, at step
62 the
run may be stopped or the S
s may be reduced to a speed at which the
KE
ss does not exceed the KE
con. If the S
s is reduced,
it may be determined that there is not an error and thus, the run may continue.
For example, the S
s may be accessed from the memory
36, the S
s
may be suitable reduced and the modified S
s may be stored to the
memory
36. Following the reduction of the S
s, the S
rotor
may be sensed at step
44. In addition, an alarm configured to alert
the user may be activated on the control interface
24.
FIG. 4 is a flow diagram illustrating steps that may be followed in accordance
with an embodiment of the step
58 as described in FIG.
3. As shown
in FIG. 4, in the check procedure described in the step
58, the R
a
is determined at steps
64 to
72, the R
d is determined
at steps
74 to
82, and the KE
ss is determined at step
84. While according to various embodiments of the invention, these values
may be determined in a variety of suitable manners, in a specific example these
values may be determined as follows.
At step
64, the S
rotor is sensed as described at step
44.
At step
66, the T
a is sensed. For example, the torque sensor
20 may sense the T
a and transmit measurements associated with
the T
a to the controller
18. In another example, the T
a
may be calculated in a manner similar to described herein with reference
to Eqn 3. At step
68, a wait time interval may be allowed to elapse. For
example, 55μ seconds may be allowed to elapse prior to sensing the S
rotor
again at step
70. At step
72, the R
a is determined.
For example, the R
a may be calculated based on a difference in the S
rotor
sensed at steps
64 and
70. This speed difference, if present,
divided by the wait time interval may be determined to be the R
a.
At step
74, the S
rotor is sensed as described at step
44.
At step
76, the motor
14 is controlled to idle. For example, the
controller
18 may transmit signals configured to facilitate an essentially
non-powered state in the motor
14. At step
78, a wait time interval
may be allowed to elapse in a manner similar to the step
68. At step
80,
following the elapse of time at step
78, the S
rotor may be sensed
again. At step
82, the R
d is determined. For example, the R
d
may be calculated based on a difference in the S
rotor sensed at
steps
74 and
80. This speed difference, if present, divided by the
wait time interval may be determined to be the R
d.
At step
84, the KE
ss, is determined. For example, utilizing
Eqn. 2, the KE
ss may be determined in response to determining the R
a
and the R
d.
At step
86, it is determined whether the KE
ss exceeds the KE
con.
If the KE
ss is essentially equal to or greater than the KE
con,
an error state may be initiated at step
88. If the KE
ss is less
than the KE
con, the run may be continued at step
90.
At step
88, an error state is initiated. For example, the control interface
24 may be controlled to display and/or sound an alarm operable to inform
the user of an error. In addition, the run may be aborted. Alternatively, at step
92, the set speed (S
s) may be reduced to a speed at which the
KE
ss is below the KE
con. For example, if a reduction of 5%
or less in the S
s will facilitate the KE
ss being below the
KE
con, the S
s may be reduced without greatly reducing the
forces experienced by any samples present in the rotor
14. Furthermore,
the duration of the run may be modified to compensate for the reduction in the
S
s. For example, the duration of the run may be increased to compensate
for a decrease in the S
s. Following the modification of the S
s,
the run may be continued at step
90.
The many features and advantages of the invention are apparent from the detailed
specification, and thus, it is intended by the appended claims to cover all such
features and advantages of the invention which fall within the true spirit and
scope of the invention. Further, since numerous modifications and variations will
readily occur to those skilled in the art, it is not desired to limit the invention
to the exact construction and operation illustrated and described, and accordingly,
all suitable modifications and equivalents may be resorted to, falling within the
scope of the invention.
*
