United States Patent 19
`Mezzatesta, Jr. et al.
`
`[54] CONTROL SYSTEM FOR REGULATING
`MOTOR SPEED
`
`[75]
`
`Inventors: Frank Mezzatesta, Jr., Glendale;
`Donald M. Young, Los Angeles, both
`of Calif.
`
`.
`:
`[73] Assignee: The Walt Disney Company, Burbank,
`Calif.
`[21] Appl. No.: 54,541
`[22] Filed:
`Apr. 27, 1993
`
`AQUIIRTANAA
`US005349276A
`[11] Patent Number:
`5,349,276
`[45] Date of Patent:
`Sep. 20, 1994
`
`.
`
`4,228,396 10/1980 Palomboet al.
`4,292,577
`9/1981 Cesarz et al.
`.
`4,305,025 12/1981 Arnold .
`4,386,398
`5/1983 Matsuoka etal. .
`4,449,082
`5/1984 Webster .
`4,492,902
`1/1985 Fickenetal. .
`4,570,110
`2/1986 Bloom et al.
`.
`4,572,999
`2/1986 Coulon,Jr. .
`4,686,437
`8/1987 Langley etal. .
`4,712,030 12/1987 Nagasawaetal. .
`4,942,344
`7/1990 Devitt et al.
`.
`5,015,927
`5/1991 Reichard .
`5,028,852
`7/1991 Dunfield .
`5,076,399 12/1991 Horbrueggeret al.
`
`.
`
`Related U.S. Application Data
`Primary Examiner—Bentsu Ro
`on
`Astarney, Agent: or Firm—Pretiy, Schrosser,
`Division of Ser. No. 843,604, Feb. 28, 1992.
`[62]
`Brueggemann & Clark
`[51] PE OUsccssveriesevsancnsecenes H02P 5/00; HO2H 7/08;
`GOI1P 3/48
`157]
`ABSTRACT
`[52] U.S. Ch, caesesscnsssnsesesseesessenneenee 318/268; 318/434;
`A motor control system accurately and reliably con-
`318/464; 388/903; 388/909
`[58] Field of Search ............... 318/565, 652, 653, 640,_trols the speed of a motorso that the motor operates in
`318/647, 463, 254, 590, 602, 618, 135, 138, 139,
`accordance with a predetermined motor speed profile,
`268, 271, 272, 434, 439, 464, 490, 494, 495,496;
`and therefore does not exceed a predetermined safe
`388/809, 814, 816, 820, 903, 907.5,909—speed, decelerates at a controlled rate, maintains a safe
`[56]
`References Cited
`minimum speed, and Py ee in ae If the
`U.S. PATENT DOCUMENTS
`indicatedand the control system halts operation of the
`Re. 32,857 2/1989 Luneau .
`motor. The motor speed is determined using an elec-
`1,438,616 12/1922 Staege .
`ni
`alyzes
`the current in at least
`3,757,183
`9/1973 Nola .
`fpaas tactinrcies tiie aaah res
`Grunlei
`two phases of the motor to provide extremely precise
`ee eh mae a
`and reliable velocity information for the motor.
`4,078,189
`3/1978 Nash etal. .
`4,208,621
`6/1980 Hipkinset al.
`
`motor operates out o
`
`ese limits, a
`
`ction is
`
`.
`
`20 Claims, 4 Drawing Sheets
`
`10
`
`
`
`
`SPEED
`FORWARD/NORMAL MONITOR 35 CONTROL
`MONITORING
`COMPUTER
`
`
`
`
`INTERFACE
`
`
`
`(RCC)
`
`UNIT
`
`
`
`RAMPING DOWN OR
`STOPPED MOTOR
`
`
`II
`of
`
`
`i
`a
`a| (")
`FREQUENCY — Per
`DRIVE
`
`
`
`
`POWER DISCONNECT COMMAND 44
`
`1
`1
`
`Mattel Ex. 2006
`Mattel Ex. 2006
`Dynacraft v. Mattel
`Dynacraft v. Mattel
`IPR2018-00038
`IPR2018-00038
`
`

`

`U.S. Patent
`
`Sep.
`
`20, 1994
`
`Sheet 1 of 4
`
`5,349,276
`
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`U.S. Patent
`
`Sep. 20, 1994
`
`Sheet 2 of 4
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`5,349,276
`
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`

`

`5,349,276
`
`Sheet 3 of 4
`
`U.S. Patent
`
`Sep. 20, 1994
`
`4
`
`

`

`U.S. Patent
`
`Sep. 20, 1994
`
`Sheet 4 of 4
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`5,349,276
`
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`

`1
`
`5,349,276
`
`CONTROL SYSTEM FOR REGULATING MOTOR
`SPEED
`
`This application is a division of a currently pending
`application, application Ser. No. 07/843,604, filed on
`Feb. 28, 1992,
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`This invention relates generally to control systems
`for motors and, more particularly,
`to motor control
`circuits that keep the speed of a motor within a prede-
`termined range.
`2. Description of the Related Art
`It often is important to control the speed of a motor
`with precision and reliability. Controlling the speed of a
`motoris especially important when the motoris used to
`operate machinery that could cause injury if the motor
`malfunctions. For example, if the motor is used to pro-
`pel an amusementride vehicle that carries passengers,a
`very specific motor speed profile must be followed with
`virtually no tolerance for error. In such an application,
`passengers can be injured if the motor speed increases
`during the ride such that the vehicle exceeds the speci-
`fied speed. Conventional motor control systems can
`adequately limit motor speed, but are not sufficiently
`reliable to provide the virtually error-free matching of
`actual motor speed to the desired motor speed profile,
`such as ramping the speed up or down, that also are
`particularly important in the case of motors that propel
`ride vehicles.
`Passengers can be injured if the actual motor speed
`does not reach the speed required in the profile, because
`the vehicle could have insufficient speed to safely nego-
`tiate the ride course. The actual motor speed also must
`follow the deceleration profile. For example, passengers
`can be injured if the motor allows the vehicle to speed
`up when the passengers are preparing to enter or exit
`the vehicle. Finally, the actual motor direction must
`propel theride vehicle in the direction commanded by
`the profile, so that the vehicle is not moved in reverse
`whena forward motion is expected. Theresult ofany of
`these improper motor operations can be catastrophic.
`Thus, the actual motor operation must match the motor
`speed profile. Many motor control systems cannot con-
`trol the actual motor operation with the extremereli-
`ability demanded for amusementpark rides.
`Various malfunctions can cause the actual motor
`speed to vary from what the commanded motor drive
`signals dictate, or can cause the drive signals to be dif-
`ferent from the signals that should be provided. A
`motor control system is used to regulate the actual
`motor performanceso that the actual speed matches the
`speed profile or at least so that the motoris shut down
`if the actual speed does not match. Effective motor
`control systems should include a means for obtaining
`reliable and accurate motor speed information that is
`easily integrated with the drive VFD.It is especially
`important to have accurate and reliable motor speed
`information if the motoris to be incorporatedintoa ride
`vehicle.
`Conventionally, the actual speed of a motoris usually
`determined by attaching a tachometerto the shaft of the
`motor. A mechanical tachometer includes a mechanism
`that is rotated by the shaft and thereby indicates the
`motor’s speed. The indicated speed is used to control
`the application of driving electrical power to the motor.
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`40
`
`45
`
`55
`
`60
`
`65
`
`6
`
`2
`The motorspeed data is relatively easy to integrate with
`the control system, but the mechanical tachometer can
`become unreliable as various parts wear out. An elec-
`tronic tachometer should provide greater reliability
`than a mechanical tachometer, and lendsitself to inte-
`gration with electronic motor drive systems. Such a
`tachometer, for example, can derive a speed signal by
`measuring the frequency of the motor current.
`From the discussion above, it should be apparentthat
`there is a need for a motor control system that can
`monitor and regulate motor performance with compa-
`rable accuracy and a higher degree ofreliability than is
`achieved conventionally, and that can be much more
`easily incorporated into a motor drive system for con-
`trol of the motor speed. The presentinventionsatisfies
`this need.
`
`SUMMARYOF THE INVENTION
`
`A motor control system in accordance with the pres-
`ent invention reliably monitors the actual motor speed,
`compares it against a motor speedprofile, and produces
`command and speed monitorsignals that indicate motor
`performance. The control system includes a tachometer
`that indicates the speed of the motor and a variable
`frequency drive (VFD)that producesdrive signals for
`the motor. The command and speed monitorsignals are
`generated accordingto the speed called for by the speed
`profile and the motor speed. The control system uses
`the command and speed monitor signals to check for
`failure to operate in accordance with the speed profile
`by checking for the occurrence of particular combina-
`tions of signals that are not expected if the motor is
`properly following the speed profile. If an unexpected
`combination persists beyond an acceptable time period
`that depends on the particular combination, then the
`control system indicates a failure and halts operation of
`the motor. In this way, the control system ensures that
`the motor operates in accordance with the motor speed
`profile. The required signals can be produced by rela-
`tively simple circuitry, and a control system incorporat-
`ing such signals is easily integrated with, for example,
`the drive system that is needed for a pulse-width modu-
`lation motor.
`The speed monitorsignals represent the actual motor
`speedin relation to the motor speed profile and indicate
`when the actual motor speed is within acceptable error
`bounds. The command signals command the VFD to
`change the speed of the motor or halt the motoralto-
`gether. Self-checking is designed into the control sys-
`tem by selecting the speed monitor and commandsig-
`nals and by selecting the combinationsof signals to be
`checked suchthatthe state of the signals will change at
`least once during the motor speed profile and such that
`at least two different signals must be checked to indicate
`proper functioning at any point in the speed profile. In
`this way, false indications of malfunction are avoided
`and virtually all possible error scenarios are detected.
`By checking various combinations of the speed moni-
`. tor and commandsignals, it is possible to reliably check
`for failure modes, quickly determine the nature of a
`failure, and avoid false failure indications. For example,
`the speed monitor signals and command signals are
`selected to be either high or low. Speed monitorsignals
`can be established that are high when the speed ofthe
`motor is above a minimum that constitutes full speed,
`below a safe maximum speed, or within acceptable
`error boundsfor the deceleration rate, and that are low
`otherwise. Similarly, command signals can be estab-
`
`

`

`5,349,276
`
`3
`lished that are high when powershould be applied to
`the motor, when the motor should operate at full speed,
`or when the motor should be stopped, and are low
`otherwise.
`Proper operation of the motor is indicated by the
`intersection of signal values. For example, if the mini-
`mum full speed signal is high and the safe maximum
`speed signal is low, then the motor is running over-
`speed. If the VFD has been commanded to generate
`drive signals to operate the motorat full speed and the
`minimum full speed signal is low, then the motor has
`failed to reach full speed. To avoid false failure indica-
`tions, each possible failure combination is assigned a
`timelimit. If a combinationofsignals indicates a failure,
`then the condition must exist for at least the assigned
`time limit before operation will be halted. The time
`period for each failure combination is restarted each
`time the error condition ceases.
`A motor control system in accordance with the in-
`vention also advantageously determines the rotational
`speed and direction of the motor by using an electronic
`tachometerthat senses the current in at least two poles
`of the motor, removes the high-frequency components
`of the sensed current signals, and provides a signal that
`indicates the fundamental frequency of the sensed cur-
`rents and therefore the speed and direction of the mo-
`tor. The motor speed can therefore be monitored and
`controlled electronically without
`the reliability and
`maintenance problems associated with mechanical ta-
`chometers and with comparable accuracy. Such elec-
`tronic speed determination is relatively simple to con-
`struct andis easily integrated into the drive system of a
`motor.
`
`The frequencyof the sensed currents can be provided
`by current sensors attached to each one of the phase
`leads attached to the motor. The sensed currentsignals
`can be filtered by a low-passfilter that removes substan-
`tially all frequency components greater than the maxi-
`mum expected operating speed. The pulsed signal that
`indicates the frequencyofthe filtered currentsignal can
`be provided by a zero crossing detector that produces a
`low to high or high to low transition at each zero cross-
`ing of the filtered current signal. All of these compo-
`nents can be easily obtained and incorporated into a
`motor control system.
`Other features and advantages of the present inven-
`tion should be apparent from the following description
`of the preferred embodiments, which illustrate, by way
`of example, the principles of the invention.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG.1 is a block diagram of a motor control system
`constructed in accordance with the present invention.
`FIG, 2 is a graph that shows a typical motor speed
`profile for the motorillustrated in FIG. 1, along with
`the three status signals for the ride control computer.
`FIG.3 is a schematic diagram of an electronic ta-
`chometer in accordance with the present invention, for
`use with the motor control system illustrated in FIG.1.
`FIG.4 is a block diagram of a motor control system
`constructed in accordance with the present invention
`and applied to a linear motor.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`With reference to FIG. 1, a motor control system 10
`constructed in accordance with the present invention
`includes a variable frequency drive signal generator 12
`
`4
`(VFD)that provides a sequenceofdrive signals to each
`phase of a motor 14 and a speed monitoring interface
`unit 16 that receives speed data from a tachometer 18
`and provides speed monitor signals to a ride control
`computer 20 that, in turn, provides motor command
`signals to the VFD 12 to produce the desired drive
`signals and control the motor. The speed monitoring
`interface unit 16 monitors the motor speed received
`from the tachometer 18, compares it against a motor
`speed profile, and signals an error if there is a sufficient
`discrepancy. The ride control computer 20 checks for
`the occurrence of particular combinations of signal
`values that are not expectedif the motor 14is properly
`following the speed profile. If an unexpected combina-
`tion value persists beyond an acceptable time period
`that depends on the particular combination, then the
`control system 10 indicates a failure and halts operation
`of the motor. In this way, the control system ensures
`that the motor operates in accordance with the motor
`speed profile and does not exceed a safe speed, deceler-
`ates in a controlled, comfortable manner, and does not
`unexpectedly operate in reverse.
`The motor 14 is used, for example, in an amusement
`park ride (not illustrated) and therefore safe, reliable
`operation is of extreme importance. The control system
`10 increases the likelihood of safe operation by includ-
`ing a three-phase output contactor 22, which acts as a
`master on/off switch that can be opened to quickly
`disconnect the motor 14 from the VFD 12 and allow
`the ride vehicle to stop. The contactor 22 is closed by a
`combination of two signals, a commandsignal received
`from the ride control computer 20 over a powerdiscon-
`nect commandline 24 and a powersignal received from
`the VFD 12 over a contactor signal line 26. If either
`signal is absent, the contactor 22 will open. When the
`contactor is closed,
`it allows drive signals from the
`VED 12 to be provided to windings 13 of the motor,
`which define the motor poles and which create a mov-
`ing magneticfield that causes rotation of the rotor 15 of
`the motor. The contactor 22 produces a contactor mon-
`itor signal that is high when the contactoris closed and
`low whenthe contactoris open, and that is provided to
`the ride control computer 20 over a signal line 28.
`The tachometer 18 determines the speed of the motor
`14 and provides this data to the speed monitoring inter-
`face unit 16. In the preferred embodiment, the tachome-
`ter is an electronic tachometer, which is described in
`greater detail below, but alternatively can be a conven-
`tional
`tachometer, such as a mechanical tachometer
`attached to the shaft of the rotor 15. The speed data
`from the electronic tachometer comprises a pulse train
`that is provided to the speed monitoring interface unit
`16, which compares the speed data against the motor
`speed profile and produces three speed monitorsignals
`that are either high or low depending on whether the
`speed of the motor meets certain conditions. The sig-
`nals, for example, can be 24-volt signals generated from
`contact switches.
`The VFD 12 changes the speed of the motor 14 by
`changing the cycle time of signals it provides to the
`motor. Typically, the VFD will provide two running
`speeds, full speed and jog speed. Full speed is the nor-
`mal maximum running speed of the motor and jog speed
`is used to intermittently operate the motor and, for
`example, park a ride vehicle. This allows the ride vehi-
`cle to be precisely positioned, such as during a parking
`maneuver. The VFD 12 provides the drive signals nec-
`essary for commandingfull speed, jog speed, and ramp-
`
`0
`
`25
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`7
`
`

`

`5,349,276
`
`6 S
`
`0
`1
`
`5
`ing to and from these speeds. The VFD changes motor
`speed when it receives the commandsignals from the
`SIGNAL 3
`SIGNAL2
`IGNAL!
`
`RAMP DOWN~~FULL FORWARD
`ride control computer 20. The commandsignals, for
`OR STOP
`SPEED
`NORMAL MEANING
`example, can be 24-volt signals provided by contact
`switches.
`0
`0
`0
`RUNNINGIN
`REVERSE
`The upper part of FIG. 2 showsa typical motor speed
`(REVERSE
`profile for the motor 14. The speed profile illustrates the
`ERROR)*
`RUNNING
`desired motor speed for a given elapsed time after an
`BELOW FULL
`initial time T0. From an initially stopped condition at
`SPEED
`time TO, the motor is commanded toits full speed and
`RUNNING TOO
`FAST
`therefore the motor speed ramps up from zero at time
`(OVERSPEED
`TO to full speed at time T3. After a time interval of
`ERROR)*
`operatingat full speed, the motor is commanded to stop
`RUNNING FULL
`SPEED
`and therefore the motor speed ramps down from full
`STOPPED
`speed at time T4 to motorstop at time TS. The preci-
`RAMPING DOWN
`sion with which the control system 10 operates is illus-
`AND BELOW
`trated by the fact that the elapsed time from T4 to T8
`FULL SPEED
`RAMPING DOWN
`for motor deceleration is approximately one second.
`AND RUNNING
`Error bounds are established for the speed of the
`TOO FAST*
`motor 14 during the motor speed profile. The error
`RAMPING DOWN
`AND AT
`bound forthe full speed of the motor represents a range
`FULL SPEED
`of acceptable speed above and below thefull speed. The
`“error modes
`maximum acceptable full speed is designated in the
`FIG. 2 graph as “Fuli+” and the minimum acceptable
`full speed is designated as “Full—.” The Full+ and
`Full— levels should be set such that when the motor 14
`is cruising at full speed, any normal fluctuations or noise
`in the speed signal obtained from the tachometer 18 will
`stay within an acceptable range between Full+ and
`Full—. The acceptable rangeis typically quite narrow.
`For example, if the frequency of pulse-width signals
`provided by the VFD 12 is 60 Hz for the motorat full
`speed, then the maximum acceptable Full+ frequency
`is 62 Hz and the minimum acceptable Full— frequency
`is 58 Hz.
`The error bound for a motor 14 to be moving andstill
`considered stoppedis designated “0+”andis set above
`absolute zero speed. The 0+ error bound exists be-
`cause, before the motor actually reaches absolute zero
`speed, it reaches a speed that for all practical purposes
`is zero. A collision of the ride vehicle at or below the
`0+ speed would cause no harm to the passengers. For
`example, using the full speed drive signal frequency of
`60 Hz, the 0-+- level is set to approximately 6 Hz. Prefer-
`ably, the 0+ level is greater than the jog speed level
`(illustrated in the graph extending between time T6 and
`time T7) so that no out of boundindication will be
`generated when the motor is ramped down from any
`speed to jog speed and then to a stop.
`An error bound for motor speed when the motor 14
`is decelerating, or ramping down to zero, provides a
`deceleration corridor designated in FIG.
`2
`as
`“Ramp+” and “Ramp—” speed. The extent of the
`deceleration corridor will depend on the ride path and
`the nature oftheride, but is set to provide an acceptable
`deceleration of the ride vehicle.
`Referring back to FIG. 1, the three status signals
`produced by the speed monitoring interface unit 16
`comprise a Ramping-Down-or-Stopped monitor signal,
`a Full-Speed monitor signal, and a Forward/Normal-
`Speed monitor signal that are sent oversignal lines 30,
`32, and 34, respectively. The following table shows the
`states of these three signals and their respective mean-
`ings:
`
`The conditions for generating the speed monitoring
`signals are selected to maximize safety so that when the
`status signals indicate error conditions, described fur-
`ther below, they ensure that all possible motor speed
`and direction malfunctions are detected. For example,
`the three monitor signals are selected such that, at least
`once during the normal motor speed profile, each moni-
`tor signal should changestate, or change from low to
`high. If one of the signals does not changestate at all
`during the monitoring period, then an erroris indicated
`by the ride control computer 20.
`With reference to FIG. 2, when the speed of the
`motor 14 is within the deceleration corridor between
`Ramp-+ and Ramp— speed and is ramping downto a
`stop, or is below the 0+ speed,
`then the Ramping-
`Down-or-Stopped monitor signal is on, or has a high
`value. When this monitorsignal is high, it indicates that
`the motoris slowing down oris almost stopped.If the
`actual deceleration of the motor when decelerating is
`too shallow oris too steep, as dictated by the Ramp+
`and Ramp— levels, respectively,
`then the Ramping-
`Down-or-Stopped monitor signal will be low. The
`range of motor speed values for this signal is illustrated
`by the arrows marked 36 and 38 and the corresponding
`signal 39 is indicated in the lower portion of FIG.2.
`The Full-Speed monitorsignal is on,oris set to a high
`value, when the actual motor speed is greater than the
`Full— level. The range of motor speed values for this
`signal is represented in the upper part of FIG. 2 by the
`vertical arrow 40 and the corresponding signal 41 is
`indicated in the lower portion of FIG. 2. Whenthis
`signal is high, it indicates that the motor 14 is running at
`or aboveits full speed.
`is set
`The Forward/Normal-Speed monitor signal
`high when the motorspeed is greater than the 0+ value
`and less than the Full+ speed value. The range of
`motor speed values for this signal is represented in the
`upper portion of FIG. 2 by the arrow 42 and the corre-
`sponding signal 43 is indicated in the lower portion of
`FIG. 2. Whenthis signal is high, it indicates that the
`motor 14 is running in a forward direction and is not
`running aboveits full speed.
`
`30
`
`45
`
`8
`
`

`

`7
`The speed monitoring interface unit 16 includes pro-
`gramming that is stored in non-volatile EPROM inte-
`grated circuits. The software in the speed monitoring
`interface unit generates these signals according to a
`precise methodology based on the information obtained 5
`from the tachometer 18, according to the signal that
`will be produced. For example, the Ramping-Down-or-
`Stopped monitorsignal is determined by examining the
`velocity indicated from the tachometer as well as the
`rate of change of that velocity. In particular, if the 10
`velocity of the motor 14 is greater than or equal to an
`absolute stopped condition, and is less than or equal to
`the 0+ level,
`then the Ramping-Down-or-Stopped
`monitorsignal is set high. If the motor velocity is nega-
`tive, as is the case when the motor is running back- 15
`wards, the Ramping-Down-or-Stopped monitor signal
`is set low. If the motor velocity is decreasing from any
`positive speed and is decreasing within the rates speci-
`fied by the Ramp+ and Ramp-— limits, then the Ramp-
`ing-Down-or-Stopped monitor signal is set high. The 20
`speed monitoring interface unit 16 will analyze the
`speed data in the sequence listed above to determine
`whether the Ramping-Down-or-Stopped monitor sig-
`nal should be set high or low. Therefore, if the motor
`velocity is decreasing but is negative, then the Ramp- 25
`ing-Down-or-Stopped monitor signal will be properly
`set low.
`taken to provide a Ramping-Down-or-
`Care is
`Stopped monitor signal whose output is steady. Thus,
`the speed monitoring interface unit 16 ensures that, if 30
`the motor 14is at full speed, then the Ramping-Down-
`or-Stopped signal will remain low, even if there is noise
`on the speed signal from the tachometer 18. Moreover,
`when the motor begins ramping down to a stop, the
`Ramping-Down-or-Stopped monitor
`signal
`remains 35
`high, even with noise on the speed signal, until the
`motor speed reaches absolute zero. If the 0+ level is
`above the jog speed level, then this monitor signal re-
`mains high while the motor runs at jog speed. This is
`illustrated in the lower portion of FIG. 2, which shows 40
`that the Ramping-Down-or-Stopped monitor signal is
`set low when the motorspeed is greater than 0+ at time
`T1 and is set high when ramping down beginning at
`time T4 through time TS.
`The speed monitoring interface unit 16 sets the Full- 45
`Speed monitoring signal to a high value by examining
`the velocity of the motor 14 as provided by the tachom-
`eter 18. If the motor velocity is greater than or equal to
`the Full— level, then the Full-Speed monitoring signal
`is set high, and the signal is otherwise set low. Also, if 50
`the motoris running in reverse, the Full-Speed monitor-
`ing signal is set low.
`The speed monitoring interface unit 16 produces the
`Forward/Normal-Speed monitor signal by examining
`the velocity of the motor 14. If the motor velocity is 55
`greater than or equal to the 0+ level and less than or
`equal to the Full+ level, then the Forward/Normal-
`Speed monitor signal is set high and otherwise is set
`low. Also, if the motor speed indicates the motoris
`running in reverse, then the Forward/Normal-Speed 60
`monitor signal is set low.
`Theride control computer 20 operates according toa
`clock cycle and therefore receives updated signals at
`regular clock intervals. The ride control computer pro-
`duces four commandsignals in response to the three 65
`status signals it receives from the speed monitoring
`interface unit 16 and in response to the Contactor moni-
`tor signal it receives from the contactor 22. Three of the
`
`9
`
`5,349,276
`
`8
`command signals produced by the ride control com-
`puter are provided to the VFD 12 oversignal lines44,
`46, and 48, and comprise a Motor Run commandsignal,
`a Motor Speed command signal, and an Emergency
`Stop commandsignal, respectively.
`The Motor Run commandsignal is set high by the
`ride control computer 20 whenever the ride control
`computer determines that the VFD 12 should operate
`the motor 14. This is determined by comparingthestate
`of the ride and operator inputs against the speed profile.
`The Motor Speed commandsignal selects the speed at
`which the motor will run, full speed or jog speed. The
`Motor Speed commandsignal is set high whenthe ride
`control computer wants the motorto run at full speed
`and is set low when it wants the motor to run at jog
`speed. The Emergency Stop commandsignalis set high
`at all times when the ride control computer determines
`that the motor 14 should be operated. Thesignal is low
`only whenthe ride control computer 20 wants the VFD
`12 to perform an emergency deceleration to a complete
`stop. Finally, the Power Disconnect commandsignal is
`a fail-safe signal that closes the contactor 22 and enables
`the motor 14 to be driven by the VFD 12. If the signal
`is set low, the contactoris open and the motor 14 cannot
`run.
`
`Theride control computer 20 selects combinations of
`command signals and monitor signals, checks their sta-
`tus against expected values, and halts operationif dis-
`agreementpersists beyonda set time period by generat-
`ing the Power Disconnect command signal. The ride
`control computer detects failure modes by using a pro-
`grammable logic controller that implements in soft-
`ware, what are known to those skilled in the art as
`disagreement timers. In operation, at each point in the
`motor speed profile graph in the upper portion of FIG.
`2 and for various predetermined combinations of the
`commandsignals and monitorsignals, there is a correct
`state. Whenever a commandsignal/monitor signal com-
`bination is not in the correct state, they are said to dis-
`agree and the ride control computer 20 software will
`keep track of the time during which there is disagree-
`ment. If the time during which there is disagreement
`exceeds safe limits, ie., if a particular disagreement
`timeris allowed to run fora sufficient period so thatit
`reaches a predeterminedelapsed time, different for each
`timer, then the ride control computer 20 indicates a
`failure and initiates a failure response, usually a shut-
`downof the motor 14. The ride control computerresets
`the elapsed time for each disagreement timer to zero
`whenever a particular command signal/monitor signal
`combination is in the correct state, or is in agreement.
`In the preferred embodiment, the ride control com-
`puter 20 software implements nine disagreementtimers.
`Thefirst disagreementtimeris referred to as the Failed-
`to-Run timer and is set to indicate a failure when the
`Motor Run command signal and Contactor monitor
`signal are in disagreementfor the timeit ordinarily takes
`the contactor 22 to close. The two signals are in dis-
`agreement, for example, when the Motor Run com-
`mandsignal is high and the Contactor monitorsignal is
`low. The second disagreement timer is a Failed-to-Stop
`timer, and is set to indicate a failure when the Motor
`Run commandsignal is low and the Contactor monitor
`signal is high, and the signals are in this condition for
`the time it ordinarily takes the motor 14 to stop from
`full speed,plus the timeit ordinarily takes the contactor
`22 to open. The next disagreementtimer is the Failed-
`to-Run-Forward disagreement
`timer and indicates a
`
`

`

`9
`failure when the Motor Run command and Motor
`Speed commandsignals are high and the Forward/Nor-
`mal monitor signal is low, and are in this condition for
`the time it ordinarily takes the motor to go from a
`stopped condition to the 0+ level.
`Theride control computer 20 software implements a
`Failed-to-Run-Full-Speed disagreement timer that indi-
`cates a failure when the Motor Run command signal
`and Motor Speed commandsignal are high, the Full-
`Speed monitor signal is low, and the signals are in this
`condition for the time it ordinarily takes the motor 14 to
`ramp upto full speed. A Running-in-Reverse disagree-
`ment timer indicates a failure when the Ramping-
`Down-or-Stopped monitor signal, Full-Speed monitor
`signal, and Forward/Normal-Speed monitor signal are
`all low and remain in that condition for the maximum
`input update time for the ride control computer 20. A
`Running-Overspeed disagreement timerindicatesa fail-
`ure when the Full Speed monitorsignal is high and the
`Forward/Normal-Speed monitor signal is low for the
`maximum input update time of the ride control com-
`puter. A Failed-to-Decelerate disagreement timer indi-
`cates a failure when the Motor Run commandsignal is
`high, the Motor Speed command signal is low, the
`Ramping-Down-or-Stopped monitorsignal is low, and
`the signals remain in this condition for the maximum
`time ordinarily required for the tachometer 18 to indi-
`cate a ramping down condition. A Failed-to-Stop dis-
`agreement timer indicates a failure when the Motor Run
`command signal is low,
`the Forward/Normal-Speed
`monitor signal is high, and the signals are in this condi-
`tion for the time it ordinarily takes the motor 14 to ramp
`down from full speed to the 0+ level. Finally, the ride
`control computer 20 software implements a Failed-to-
`Accelerate disagreement timer that indicates a failure
`when the Motor Run commandsignal, Full Speed com-
`mandsignal, and the Ramping-Down-or Stopped moni-
`tor signal are high, and the signals are in this condition
`for the time it ordinarily takes the motor 14 to ramp up
`to full speed.
`The motor control system 10 described above advan-
`tageously provides safe and reliable control of motor
`speed with theinclusion of an electronic tachometer. In
`particular, the preferred embodimentincludes an elec-
`tronic tachometer 18 that does not require any moving
`parts and that reliably provides accurate speed informa-
`tion andis easily incorporated with the other elements
`of the motor control system discussed above. The elec-
`tronic tachometer achieves these benefits by analyzing
`the curr