(12) United States Patent
`Kessler
`
`(lo) Patent No.:
`(45) Date of Patent:
`
`US 6,323,611 B1
`Nov. 27, 2001
`
`III III IIH IIHI 1011
`
`I DIII I IDI II DII II DI II
`
`(54) CIRCUIT FOR OPERATING AN ELECTRIC
`MOTOR
`
`(75)
`
`Inventor: Martin Kessler, Buehl (DE)
`
`(73) Assignee: Robert Bosch GmbH, Stuttgart (DE)
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 490 days.
`
`(21)
`
`(22)
`
`(86)
`
`Appt. No.:
`
`08/793,365
`
`PCT Filed:
`
`Aug. 24, 1995
`
`PCT No.:
`
`PCT /DE95/01123
`
`§ 371 Date:
`
`Feb. 24, 1997
`
`§ 102(e) Date: Feb. 24, 1997
`(87) PCT Pub. No.: W096/08066
`
`PCT Pub. Date: Mar. 14, 1996
`Foreign Application Priority Data
`
`(30)
`
`(DE) ................. ............................... 44 32 058
`
`Sep. 9, 1994
`Int. Cl.'
`(51)
`(52) U.S. Cl.
`
`......................... ............................... HO2P 7/06
`. 318/430; 318/434; 318/461;
`388/903; 388/921
`(58) Field of Search ...... ............................... 318/430 -434,
`318/461, 463, 471, 473, 484; 388/903,
`921, 934
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`2/1973 Larson .
`3,716,772 *
`2/1976 Gay .
`3,936,711 *
`4,063,112 * 12/1977 Dumbeck ............................. 318/490
`
`4,307,325 * 12/1981 Saar .
`2/1982 Gille et al.
`4,314,186 *
`4/1985 Fasset et al.
`4,514,670 *
`7/1985 Sharp et al.
`4,528,898 *
`9/1985 Ohyama .
`4,541,029 *
`2/1987 Iizawa et al.
`4,641,067 *
`5,317,244 *
`5/1994 Ishikura
`5,585,705 * 12/1996 Brieden
`
`.
`
`.......... ......... ...... 318/434
`318/467
`
`318/287
`318/254
`318/467
`
`FOREIGN PATENT DOCUMENTS
`
`2228715 * 12/1972
`3034118
`3/1982
`0413893 *
`2/1991
`60 -5797 *
`1/1985
`
`(DE) .
`(DE) .
`(EP) .
`(JP) .
`
`* cited by examiner
`
`Primary Examiner -Bentsu Ro
`(74) Attorney, Agent, or Firm Venable; George H.
`Spencer; Allen Wood
`
`(57)
`
`ABSTRACT
`
`A circuit for operating an electric motor (11) includes a
`monitoring arrangement (24) for ascertaining an increased
`load state of the electric motor (11). The monitoring arrange-
`ment (24) compares an rpm difference (ND) between a
`predetermined nominal rpm value (Nsoza) and an actual
`rpm value signal (N,ST) with a predetermined limit value. If
`the limit value is exceeded, the monitoring arrangement (24)
`emits an overload signal (25) that reduces the nominal rpm
`value (NSOLL) or a control variable (SN) supplied to a drive
`stage (18), or drops it to zero. The circuit is particularly
`suited for use with a fan, in which instance the ventilator
`(22) cools the electric motor (11) and /or the drive stage (18).
`
`18 Claims, 1 Drawing Sheet
`
`24
`MONITORING
`
`21
`
`15 SENSOR
`
`11 MOTOR
`
`NISI
`
`10
`
`26 TIMER
`
`27 TIMER
`
`UM
`
`28 TIMER
`
`VALUET
`GENERATOR
`
`17 CONTROL
`VARIABLE
`LIMITER
`
`,-r
`
`5
`
`14
`
`NSOLL
`
`N'SOLL
`
`12
`NOMINAL
`VALUE
`GENERATOR
`
`13
`NOMINAL
`VALUE
`REDUCER
`
`REGULATOR
`
`16
`
`RA
`
`18
`
`(
`SN
`
`l
`
`DR VE
`STAGE
`
`20
`
`ARMANRE RESISTANCE
`
`23b
`
`23b
`
`COOLING
`BODY
`
`19
`
`

`

`UUSI, LLC
`Exhibit 2034
`2/7
`
`19
`
`_t-20
`
`SN
`
`BODY
`
`COOLING
`
`STAGE
`DRIVE
`
`23b
`
`23b
`
`ARMATURE RESISTANCE
`
`18
`
`RA
`
`FIG. 1
`
`16
`
`REGULATOR
`
`REDUCER
`
`VALUE
`NOMINAL
`
`13
`
`N'SOLL
`
`NSOLL
`
`GENERATOR
`
`VALUE
`
`NOMINAL
`
`12
`
`1
`
`LIMITER
`VARIABLE
`17 CONTROL
`
`GENERATOR
`VALUE
`I29 LIMIT
`
`UM-
`
`28 TIMER
`
`27 TIMER
`
`26 TIMER
`
`14
`
`2
`
`11 MOTOR
`
`15 SENSOR
`
`21
`
`ARRANGEMENT
`
`MONITORING
`
`24
`
`

`

`US 6,323,611 Bl
`
`1
`CIRCUIT FOR OPERATING AN ELECTRIC
`MOTOR
`
`BACKGROUND OF THE INVENTION
`
`5
`
`Related Art
`The invention is based on a circuit for operating an
`electric motor, of the type having an arrangement that
`produces a signal serving as a measure for the rpm of electric
`motor and having a monitoring arrangement for detecting an
`increased load state of the electric motor. DE -PS 30 34 118
`discloses a generic circuit that has a sensor which produces
`a signal serving as a measure for the rpm of the electric
`motor. The known circuit includes a monitoring arrange-
`ment for ascertaining an increased load state of the electric 15
`motor; the arrangement monitors rpm, comparing the actual
`rpm determined from the sensor signal to a predetermined
`limit value. The limit value is derived from an initial actual
`rpm value established after a predetermined time following
`startup of the known circuit. The known circuit for operating
`an electric motor is used in electronic monitoring of an
`opening and closing process of electrically -operated motor
`vehicle parts. The limit value is tailored to the task of
`detecting jammed objects or body parts. The known circuit
`is not provided with an increased load state of the electric 25
`motor, or of a provided end stage, that can lead to a thermal
`overload of these parts.
`
`2
`Aparticularly advantageous modification of the circuit of
`the invention provides that the limit value for the rpm
`difference, which is provided in the monitoring arrangement,
`is determined as a function of the predetermined nominal
`rpm value. With this measure, the limit value can be adapted
`to different operating relationships.
`An advantageous embodiment provides that the predeter-
`mined nominal rpm value is reduced when the overload
`signal is emitted. With another advantageous measure, when
`the overload signal occurs, a control variable of a controlled
`voltage source is reduced, which source is instrumental in
`the actuation of the drive stage. Implementing one of these
`measures ensures that, despite an increased load state, the
`electric motor can continue to be operated reliably without
`the threat of thermal destruction.
`In a particularly advantageous modification, the monitor-
`ing arrangement does not emit the overload signal until a
`predeterminable period of time has passed. The predeter-
`minable time is a delay time that takes into account the
`run -up of the electric motor, for example starting from the
`off state. The unsteady state that occurs during mn -up and
`could lead to erroneous generation of the overload signal can
`be kept in check with this measure.
`Another advantageous modification provides that the
`overload signal is suppressed following a predetermined
`time. If the electric motor is further overloaded, the overload
`signal is emitted again. In this operation, periodic attempts
`are made to turn on the electric motor. The times during
`which the overload signal occurs or is suppressed are
`advantageously measured such that, despite an overload or
`complete blockage of the electric motor, the average power
`is limited to a value that does not represent a danger of
`thermal overload of the electric motor and /or the drive stage.
`Further advantageous embodiments and advantageous
`modifications discussed in the description below.
`
`BRIEF DESCRIPTION OF THE DRAWING
`
`The drawing FIGURE shows a block diagram of a circuit
`of the invention for operating an electric motor.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`The FIGURE shows an rpm -regulating circuit 10 that
`regulates the rpm of an electric motor Il at a predetermined
`command or rpm value NsoLL. The nominal rpm value
`NsoLL, is produced by a command or nominal value gen-
`erator 12. The nominal value generator 12 transmits the
`nominal rpm value NsoLL to a nominal value reducer 13,
`which conducts the nominal rpm value Nsom, further, as a
`limited nominal rpm value N'soLL, to an adder 14. The adder
`14 forms an rpm difference ND between the limited nominal
`rpm value N'soLL and an actual rpm value signal Nisi. The
`actual rpm value signal NIST is a measure for the rpm of the
`electric motor 11 that is produced by an rpm sensor 15.
`The adder 14 transmits the rpm difference ND to a
`regulator 16 that determines a control variable SN. The
`regulator 16 includes a control variable limiter 17. The
`control variable SN enters an end stage or drive stage 18
`connected to a heat sink or cooling body 19. The drive stage
`18 connects the electric motor 11 to an energy source, not
`shown in detail, by way of a first connection 20 and a second
`connection 21. The drive stage 18 is controlled with the
`control variable SN in such a way that the rpm of the electric
`motor 11 corresponds to the predetermined nominal rpm
`value NSOLL
`
`UUSI, LLC
`Exhibit 2034
`3/7
`
`30
`
`40
`
`SUMMARY OF THE INVENTION
`It is the object of the invention to provide a circuit for
`operating a motor that in particular assures the protection of
`an end or drive stage and /or the electric motor against
`thermal overload.
`The object is accomplished by a circuit of the above
`mentioned type which is characterized in that the monitoring 35
`arrangement compares an rpm difference, between a prede-
`termined nominal rpm value and the actual rpm determined
`from the actual rpm signal, to a predetermined limit value,
`and emits an overload signal if the limit value is exceeded.
`A monitoring arrangement provided in accordance with
`the invention compares the difference between a provided
`nominal rpm value and an actual rpm value determined from
`a sensor signal. If the limit value is exceeded, the monitoring
`arrangement emits an overload signal.
`The concept underlying the circuit of the invention is that, 45
`in the steady operating state, the difference between the
`predetermined nominal rpm value and the detected actual
`rpm value either lies within specific limits as a function of
`a predetermined rpm regulator or is zero. Sluggishness of the
`electric motor or of a part driven by the motor, as well as
`complete blockage, cause the limit value to be exceeded, and
`thus lead to triggering of the overload signal.
`An advantage of the circuit of the invention for operating
`an electric motor is that an increased load state or complete 55
`blockage can be recognized with electrical signals that can
`be detected with simple means. No further sensors, such as
`a temperature sensor, are necessary.
`The circuit of the invention for operating an electric motor
`is particularly suited for use in a fan, in which instance the 60
`fan is used to cool an electric motor and /or the drive stage
`simultaneously.
`In comparison to establishing a limit value based on a
`predetermined rpm value, the circuit of the invention for
`operating an electric motor has the advantage that both the 65
`electric motor and the drive stage only need to be designed
`for low thermal stress.
`
`50
`
`

`

`US 6,323,611 Bl
`
`15
`
`35
`
`3
`A current flowing through the electric motor 11 leads to a
`motor voltage UM, which corresponds to the voltage drop at
`an armature resistance RA, to which an electric -motor coun-
`tervoltage (EMK) is added.
`The electric motor 11 actuates a ventilator 22 that emits a 5
`first air current 23a in the direction of the electric motor 11
`and a second air current 23b in the direction of the cooling
`body 19.
`The rpm difference ND and the nominal rpm value Nsou
`are supplied to a monitoring arrangement 24 that produces 1°
`an overload signal 25, which is transmitted to both the
`nominal value reducer 13 and the control variable limiter 17.
`The monitoring arrangement 24 includes a first, a second
`and a third timer 26, 27 and 28, respectively, and a limit
`value generator 29.
`The illustrated circuit of the invention for operating the
`electric motor 11 operates as follows:
`The rpm- regulating circuit 10 regulates the rpm of the
`electric motor 11 in such a way that the rpm difference NIST
`between the nominal rpm value NSOLL produced by the
`nominal value generator 12 and the actual rpm value signal
`NIST produced by the rpm sensor 15 is as low as possible, or
`is even zero. To regulate the rpm, the rpm -regulating circuit
`10 includes the adder 14, which determines the rpm differ- 25
`ence ND, as a deviation, from the actual rpm value signal
`NIST and the limited nominal rpm value N'soLL. The regu-
`lator 16 establishes the control variable SN as a function of
`the rpm difference Nd. The regulator 16 can be configured in
`accordance with the extensive background literature on 30
`regulating technology, for example as a proportional or
`proportional- plus -integral regulator. Both analog and digital
`regulators are suitable. The control variable SN can be an
`analog signal that is supplied to the drive stage 18. The
`control variable SN is preferably a digital, pulse -width-
`modulated signal that effects a clocked operation in the drive
`stage 18. In this clocked operation, the electric motor 11 is
`connected to the energy source not shown in detail, or
`completely shut off, in rapid temporal sequence. The result
`is an average voltage UM, that leads to a specific motor 40
`current as a function of the load set by the ventilator 22. The
`drive stage 18 can be characterized as a controlled voltage
`source that sets the motor voltage UM variably at a value at
`which the rpm difference ND is as low as possible or is zero.
`The clocked operation of the drive stage 18 with the pulse 45
`width control permits the drive stage 18 to be designed for
`a switching operation that results in minimal energy loss in
`the drive stage 18 that must be dissipated via the cooling
`body 19. The cooling body 19 is either separate and con-
`nected to the end stage 18, or a specially- worked component
`of the drive stage 18.
`The rpm of the electric motor 11 is detected by the rpm
`sensor 15. It is emphasized that the rpm of the ventilator 22
`or the rpm of a drive not shown in detail can also be detected
`instead of the motor rpm. The only essential point is that the 5s
`rpm sensor 15 produces the actual rpm value signal Nis,. as
`a measure for the rpm of the electric motor 11.
`The rpm sensor 15 may operate on, for example, an
`optoelectronic basis. A light barrier is suitable. The rpm
`sensor 15 preferably operates on a magnetic basis, for
`example detecting a magnetic field. Hall sensors, magne-
`toresistive elements or inductive receivers are examples of
`suitable devices. The detection of commutations signal
`components in the motor current is also particularly suited.
`The rpm is preferably detected indirectly through the evalu- 65
`ation of the operating data of the electric motor 11. The rpm
`is proportional to the induced countervoltage, which in turn
`
`50
`
`60
`
`4
`can be determined from the motor terminal voltage and the
`motor current with a known internal resistance.
`A feature of the circuit is the monitoring arrangement 24
`that compares the rpm difference ND to the limit value
`produced by the limit value generator 29. If the rpm differ-
`ence ND exceeds the limit value, the monitoring arrange-
`ment 24 emits the overload signal 25. The overload signal 25
`can trigger a warning signal, for example. In the illustrated
`embodiment, the overload signal 25 can, for example, lower
`the nominal rpm value NsoLLpredetermined by the nominal
`value generator 12 by a predetermined amount, or even
`make it zero, in the nominal value reducer 13. The lowered
`nominal rpm value NsoLL is characterized as a limited
`nominal rpm value N'SOLL that is supplied to the adder 14.
`It is also possible for the overload signal 25 to lower, for
`example, the control variable SN of the regulator 16 by a
`predetermined amount or to zero with the control variable
`limiter 17 included in the regulator 16.
`A particularly advantageous embodiment provides that
`the limit value produced by the limit value generator 29 is
`established as a function of the predetermined nominal rpm
`value N50Ly. Therefore, in addition to the rpm difference
`ND, the nominal rpm value Nso2L is supplied to the moni-
`toring arrangement 24 as an input signal. With a high
`nominal rpm value Nso2L the limit value is preferably
`established to be lower than with a lower nominal rpm value
`NSOLL
`Another advantageous embodiment includes the first
`timer 26 in the monitoring arrangement 24. The first timer 26
`is set at a time that corresponds to the mn -up of the electric
`motor 11, for example from standstill to the predetermined
`normal- rating operation, at which the nominal rpm value
`Nsou is reached. During the time predetermined by the first
`timer 26, emission of the overload signal 25 is suppressed.
`The first timer 26 recognizes the turning on of the electric
`motor 11, for example through a change in the presetting of
`the nominal rpm value NsoLL.
`The second and third timers 27, 28 permit a periodic,
`recurring attempt to start up the electric motor 11 despite an
`ascertained overload state or increased -load state. The sec-
`ond timer 27 starts, for example, simultaneously with the
`occurrence of the overload signal 25. The time set by the
`second timer 27 therefore establishes the shutoff time of the
`electric motor 11 or the time of reduced power. After the
`time predetermined by the second timer 27 has expired, the
`overload signal 25 is suppressed during the time predeter-
`mined by the third timer 28. Therefore, during the time
`predetermined by the third timer 28, an attempt is made to
`resume normal- rating operation of the electric motor 11 with
`the predetermined nominal rpm value NsoLL A temporary
`blocked state or temporary sluggishness is identified with
`this measure, and has no further effects on continued opera-
`tion. Because the third timer 28 predetermines a turn -on time
`and the second timer 27 predetermines a shutoff time or the
`time of reduced power, it is possible to keep thermal
`overload of both the electric motor 11 the drive stage 18
`cooled by the cooling body 19 within preset limits, even if
`overload occurs during long -term unsteady operation. A
`suitable setting can be selected, for example, in that the
`average current IM flowing through the electric motor 11 is
`selected to meet the following condition:
`
`/,=T,,l(T,, +Tas)x(Uer..
`
`/RA)
`
`where Te3n is the turn -on time, Taus is the shutoff time and
`UM,,,ax is the maximum motor voltage. Thermal overload is
`precluded with an average motor current set in this way.
`
`UUSI, LLC
`Exhibit 2034
`4/7
`
`

`

`US 6,323,611 Bl
`
`5
`
`15
`
`30
`
`5
`A preferred use of the circuit of the invention for oper-
`ating an electric motor 11 is in a fan, preferably one disposed
`in a motor vehicle and serving to ventilate the interior. A
`modification of the use in a fan in accordance with the
`invention provides that the drive stage 18 and /or the electric
`motor 11 is or are cooled by the air current 23a 23b of the
`ventilator 22 itself. With this measure, it is possible to
`provide an inexpensive end stage 18 whose permissible
`continuous energy loss can have a lower value than a drive
`stage 18 that does not benefit from additional cooling. A io
`crucial feature of this modification, therefore, is that, when
`the electric motor 11 is sluggish or complete blockage exists,
`the motor current in the drive stage 18 and therefore the
`energy loss of the drive stage are reduced after the additional
`cooling by the ventilator 22 has ended.
`A transistor, preferably a field -effect transistor, is particu-
`larly suited to be the drive stage 18. In a bipolar transistor,
`the control variable SN is a control current that flows into the
`base during analog operation. In a field -effect transistor, the
`control variable SN is a control voltage that impinges upon 20
`the gate. In all cases, a pulse -width -modulated, digital
`control variable SN is provided in clocked operation; this
`variable operates the drive stage 18 as a controlled voltage
`source that predetermines the average motor voltage Um.
`In principle, it is also possible to operate the circuit of the 25
`invention without an rpm -regulating circuit 10. Instead of
`rpm regulation, an rpm control is provided, with the moni-
`toring arrangement 24 detecting the rpm difference ND in
`controlled operation, just as in the former case.
`What is claimed is:
`1. An improved circuit for operating a DC electric motor,
`the circuit having an arrangement that produces a signal
`serving as a measure for the rpm of the electric motor and
`having a monitoring arrangement for detecting an increased
`load state of the electric motor, wherein the improvement 35
`comprises:
`the monitoring arrangement (24) compares an rpm dif-
`ference (ND) between a predetermined nominal rpm
`value (Nsozz,) and the actual rpm determined from the
`actual rpm value signal (N,-) to a predetermined limit 40
`value, and emits an overload signal (25) if the limit
`value is exceeded.
`2. A circuit according to claim 1, wherein the limit value
`is a function of the predetermined nominal rpm value
`(Nsozz)
`3. A circuit according to claim 1, wherein the monitoring
`arrangement (24) includes a first timer (26) that takes into
`account a run -up process of the electric motor (11) with
`respect to setting of the nominal rpm value Mom) by
`suppressing the overload signal (25).
`4. A circuit according to claim 1, wherein the arrangement
`that produces a signal serving as a measure for the rpm
`includes an rpm sensor.
`5. A circuit according to claim 1, wherein the arrangement
`that produces a signal serving as a measure for the rpm 55
`detects the motor current and the motor terminal voltage,
`and determines the rpm from the detected motor current and
`the motor terminal voltage.
`6. A circuit according to claim 1, in combination with a
`fan that is driven by the electric motor (11), wherein the
`circuit further comprises a drive stage (18) for driving the
`electric motor (11) and the fan cools at least one of the
`electric motor (11) and the drive stage (18) using air cur-
`rents.
`7. An improved circuit for operating a DC electric motor,
`the circuit having an arrangement that produces a signal
`serving as a measure for the rpm of the electric motor and
`
`45
`
`50
`
`60
`
`65
`
`6
`having a monitoring arrangement for detecting an increased
`load state of the electric motor, wherein the improvement
`comprises:
`the monitoring arrangement (24) compares an rpm dif-
`ference (ND) between a predetermined nominal rpm
`value (N50,) and the actual rpm determined from the
`actual rpm value signal (NJST) to a predetermined limit
`value, and emits an overload signal (25) if the limit
`value is exceeded; and
`the current further comprises a nominal value reducer (13)
`that receives the overload signal (25) and that lowers
`the nominal rpm value (Nsozz) to a limited nominal
`rpm value (N'sou) in response to the overload signal
`(25).
`8. An improved circuit for operating a DC electric motor,
`the circuit having an arrangement that produces a signal
`serving as a measure for the rpm of the electric motor and
`having a drive stage for driving the electric motor in
`response to a control variable, the circuit additionally having
`a monitoring arrangement for detecting an increased load
`state of the electric motor, wherein the improvement com-
`prises:
`the monitoring arrangement (24) compares an rpm dif-
`ference (ND) between a predetermined nominal rpm
`value (Nsozz) and the actual rpm determined from the
`actual rpm value signal (NJST) to a predetermined limit
`value, and emits an overload signal (25) if the limit
`value is exceeded; and
`the circuit further comprises a regulator (16) which gen-
`erates the control variable (SN) as a function of the rpm
`difference (ND), the regulator (16) including a control
`variable limiter (17) that receives the overload signal
`(25) and that reduces the control variable (SN) supplied
`to the drive stage (18) to a predetermined value in
`response to the overload signal (25).
`9. An improved circuit for operating an electric motor, the
`circuit having an arrangement that produces a signal serving
`as a measure for the rpm of the electric motor and having a
`monitoring arrangement for detecting an increased load state
`of the electric motor, wherein the improvement comprises:
`the monitoring arrangement (24) compares an rpm dif-
`ference (ND) between a predetermined nominal rpm
`value (Nsozz) and the actual rpm determined from the
`actual rpm value signal (NzsT) to a predetermined limit
`value, and emits an overload signal (25) if the limit
`value is exceeded, and
`the monitoring arrangement (24) includes a timer (27) that
`limits the duration of the overload signal (25) to a time
`(Taus) predetermined by the timer (27), and a further
`timer (28) that predetermines a time (T,,) during
`which the overload signal (25) is then suppressed.
`10. A circuit according to claim 9, further comprising a
`drive stage (18) for driving the electric motor (11), and
`wherein the two times (Tas, Tet) predetermined by the two
`timers (27, 28) are measured so as to preclude thermal
`overload of at least one of the electric motor (11) and the
`drive stage (18).
`11. A circuit for operating a motor in response to a
`nominal rpm signal, comprising:
`means for producing an actual rpm signal which serves as
`a measure of the rpm of the motor;
`means for generating a control variable signal which is a
`function of the difference between the nominal and
`actual rpm signals;
`means for comparing the difference between the nominal
`and actual rpm signals to a limit value and generating
`an overload signal if the difference exceeds the limit
`value;
`
`UUSI, LLC
`Exhibit 2034
`5/7
`
`

`

`US 6,323,611 Bl
`
`7
`means for reducing the control variable signal if the
`overload signal appears; and
`means for driving the motor in response to the control
`variable signal.
`12. A circuit according to claim 11, wherein the limit
`value is a function of the nominal rpm signal.
`13. A circuit according to claim 11, wherein the means for
`generating a control variable signal comprises an adder
`which receives the nominal and actual rpm signals and
`generates a different signal from them, and a nominal value
`reducer which reduces the nominal rpm signal before it is
`received by the adder if the overload signal appears.
`14. A circuit according to claim 11, wherein the means for
`generating a control variable signal comprises an adder
`which receives the nominal and actual rpm signals and
`generates a difference signal from then, and a regulator
`which generates the control variable signal from the differ-
`ence signal, the regulator including a control variable limiter
`
`8
`which limits the magnitude of the control variable signal if
`the overload signal appears.
`15. A circuit according to claim 11, wherein the means for
`generating an overload signal comprises a timer which
`suppresses the overload signal during run -up of the motor.
`16. A circuit according to claim 15, wherein the means for
`generating an overload signal further comprises another
`timer which limits the duration of the overload signal and an
`additional timer which then times an interval during which
`the overload signal is suppressed.
`17. A circuit according to claim 11, wherein the motor is
`a DC motor, wherein the control variable signal is a pulse -
`width modulated signal, and wherein the means for driving
`the motor selectively connects the motor to a power source
`in response to the control variable speed.
`18. A circuit according to claim 11, wherein the motor is
`a DC motor.
`
`5
`
`10
`
`15
`
`UUSI, LLC
`Exhibit 2034
`6/7
`
`

`

`UNITED STATES PATENT AND TRADEMARK OFFICE
`CERTIFICATE OF CORRECTION
`
`PATENT NO.
`DATED
`INVENTOR(S)
`
`: 6,323,611 B1
`: November 27, 2001
`: Kessler
`
`Page 1 of 1
`
`It is certified that error appears in the above -identified patent and that said Letters Patent is
`hereby corrected as shown below:
`
`Title page,
`Item [ *], Notice, delete "490" and insert -- 981 - -.
`
`Signed and Sealed this
`
`First Day of July, 2003
`
`JAMES E. ROGAN
`Director of the United States Patent and Trademark Office
`
`UUSI, LLC
`Exhibit 2034
`7/7
`
`