United States Patent
`
`[19;
`
`Mezzatesta, Jr. et al.
`
`[11]
`
`[45]
`
`Patent Number:
`
`5,349,276
`
`Date of Patent:
`
`Sep. 20, 1994
`
`I||||||||||l|||l|||||||||||Illlllllll|||l|l||||||||l|||l|||||||||||||l|||||
`USODS349276A
`
`[54] CONTROL SYSTEM FOR REGULATIING
`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]
`
`[221
`
`[62]
`
`[5 1]
`
`[52]
`
`[53]
`
`[56]
`
`App]. No:
`Filed:
`
`59,541
`
`Apr. 27, 1993
`
`Related U.S. Application Data
`Division of Ser. No. 843,604, Feb. 28, 1992.
`
`Int. CI.5 ......................... HDZP 5/00; HOZH 7/08;
`G01? 3/48
`U.S. Cl. .................................... 318/268; 318/434;
`318/464; 388/903; 388/909
`Field of Search ............... 318/565, 652, 653, 640,
`318/647, 463, 254, 590, 602, 618, 135, I38, 139,
`268, 271, 272, 434, 439, 464, 490, 494, 495, 496;
`388/809, 814, 816, 820, 903, 907.5, 909
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`Lnneaa .
`Smege .
`Noia .
`Grunleitner et al.
`Thode .
`.
`Nash et a].
`Hipkins et a].
`
`.
`
`.
`
`Re. 32,357 2/1989
`1,438,616 12/1922
`3,757,183
`9/1973
`3,916,272 10/1975
`3,969,659
`7/1976
`4,078,189 3/ 1978
`4,208,621
`6/1980
`
`4,228,396
`4,292,577
`4,305,025
`4,386,398
`4,449,032
`4,492,902
`4,5 70, 1 10
`4,572,999
`4,536,432
`4,712,030
`4,942,344
`5,015,927
`5,028,852
`5,076,399
`
`10/1980
`9/1981
`12/1981
`5/1983
`5/1984
`1/1985
`2/1986
`2/1986
`8/1987
`12/1987
`7/1990
`5/1991
`7/1991
`12/1991
`
`.
`
`.
`
`.
`.
`
`Palomho et a1.
`Cesarz et al.
`.
`Arnold .
`Matsuoka et al.
`Webster .
`Ficken et al.
`Bloom et a].
`.
`Coulon, .Tr.
`.
`Langley et a1.
`Nagasnwa et al.
`Devitt et a].
`.
`Reichard .
`Dunfield .
`Horhruegger et a1.
`
`.
`
`.
`
`Primary Examiner—Bentsu Ro
`Attorney, Agent, or Finn—Pretty, Schroeder,
`Brueggemann & Clark
`
`[57]
`
`ABSTRACT
`
`A motor control system accurately and reliably con-
`trols the speed of a motor so that the motor operates in
`accordance with a predetermined motor speed profile,
`and therefore does not exceed a predetermined safe
`speed, decelerates at a controlled rate, maintains a safe
`minimum Speed, and does not turn in reverse. If the
`motor operates out of these limits, a malfunction is
`indicated and the control system halts operation of the
`motor. The motor speed is determined using an elecF
`tronic tachometer that analyzes the current in at least
`two phases of the motor to provide extremely precise
`and reliable velocity information for the motor.
`
`20 Claims, 4 Drawing Sheets
`
`10
`
`28
`
`
`
`
`CONTACTOR MONITOR 34
`RIDE
`SPEED
`
`
`
`MONITORING
`FORWARD/NORMAL MONTTOR 32 CONTROL
`COMPUTER
`
`
`
`
`
`
`FULL SPEED MONITOR
`3:]
`(R00)
`
`WPING DOWN OR
`
`
`STOPPED MOTOR
`
`DRIVE
`
`
`
`-
`-
` FREQUENCY.
`
`'
`
`
`POWER DISCONNECT COMMAND
`
`
`44
`
`HOTOR RUN COMMAND
`45
`
`EMERGENCY STOP COMMAND
`
`1
`1
`
`Mattel Ex. 2006
`Mattel Ex. 2006
`Dynacraft v. Mattel
`Dynacraft v. Mattel
`|PR2018-00038
`IPR2018-00038
`
`

`

`US. Patent
`
`Sep.
`
`20
`
`, 1994
`
`Sheet 1 of 4
`
`5,349,276
`
`
`
`5%”meon”6:20:Sam3:mega;
`
`
`
`
`
`mm
`
`
`
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`

`

`US. Patent
`
`Sep. 20, 1994
`
`Sheet 2 of 4
`
`5,349,276
`
`LAMR.UNDDA“WWF
`
`3
`
`

`

`US. Patent
`
`Sep.20,l994
`
`Sheet 3 of 4
`
`5,349,276
`
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`US. Patent
`
`Sep. 20, 1994
`
`Sheet 4 of 4
`
`5,349,276
`
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`
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`

`

`1
`
`5,349,276
`
`CONTROL SYSTEM FOR REGUIATING 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
`motor is especially important when the motor is used to
`operate machinery that could cause injury if the motor
`malfunctions. For example, if the motor is used to pro-
`pel an amusement ride 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-
`lied 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 prepel
`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 the ride vehicle in the direction commanded by
`the profile, so that the vehicle is not moved in reverse
`when a forward motion is expected. The result of any 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 extreme reli-
`ability demanded for amusement park 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 performance so that the actual speed matches the
`speed profile or at least so that the motor is shut (10%
`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 motor is to be incorporated into a ride
`vehicle.
`
`Conventionally, the actual speed of a motor is usually
`determined by attaching a tachometer to 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
`
`35
`
`40
`
`45
`
`50
`
`55
`
`65
`
`6
`
`2
`The motor speed 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 lends itself 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 apparent that
`there is a need for a motor control system that can
`monitor and regulate motor performance with compa-
`rable accuracy and a higher degree of reliability 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 present invention satisfies
`this need.
`
`SUMMARY OF THE INVENTION
`
`A motor control system in accordance with the pres-
`ent invention reliably monitors the actual motor speed,
`compares it against a motor speed profile, and produces
`command and speed monitor signals that indicate motor
`performance. The control system includes a tachometer
`that indicates the speed of the motor and a variable
`frequency drive (VFD) that produces drive signals for
`the motor. The command and speed monitor signals are
`generated according to 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 combine
`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 monitor signals represent the actual motor
`speed in 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 motor alto-
`gether. Self-checking is designed into the control sys-
`tem by selecting the speed monitor and command sig-
`nals and by selecting the combinations of signals to be
`checked such that the 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 command signals, 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 monitor signals
`can be established that are high when the speed of the
`motor is above a minimum that constitutes full speed,
`below a safe maximum speed, or within acceptable
`error bounds for the deceleration rate, and that are low
`otherwise. Similarly, command signals can be estab-
`
`

`

`5,349,276
`
`3
`lished that are high when power should 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 motor at 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
`time limit. [fa combination of signals 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
`tachometer that 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 and is easily integrated into the drive system of a
`motor.
`
`10
`
`15
`
`20
`
`25
`
`35
`
`4
`(VFD) that provides a sequence of drive 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 expected if the motor 14 is 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 command signal received
`from the ride control computer 20 over a power discou-
`nect command line 24 and a power signal 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
`VFD 12 to be provided to windings 13 of the motor,
`which define the motor poles and which create a mov-
`ing magnetic field that causes rotation of the rotor 15 of
`the motor. The contactor 22 produces a contactor mon-
`itor signal that is high when the contactor is closed and
`low when the contactor is open, and that is provided to
`the ride control computer 2|] 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 deseribed 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 monitor signals
`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 commanding full speed, jog speed, and ramp-
`
`The frequency of the sensed currents can be provided
`by current sensors attached to each one of the phase
`leads attached to the motor. The sensed current signals
`can be filtered by a low-pass filter that removes substan-
`tially all frequency components greater than the maxi-
`mum expected operating speed. The pulsed signal that
`indicates the frequency of the filtered current signal can 40
`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
`
`45
`
`50
`
`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 motor illustrated 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
`
`55
`
`60
`
`65
`
`7
`
`

`

`5,349,276
`
`6 S
`
`SIGNAL 3
`SIGNAL 2
`IGNAL l
`FORWARD
`FULL
`RAMP DOWN
`
`
`
`NORMAL MEANINGSPEEDOR STOP
`0
`0
`0
`RUNNING IN
`REVERSE
`(REVERSE
`ERROR)‘
`RUNNING
`BELOW FULL
`SPEED
`RUNNING TOO
`FAST
`(OVERSPEED
`ERROR)‘
`RUNNING FULL
`SPEED
`STOPPED
`WING DOWN
`AND BELOW
`FULL SPEED
`RAMPING DOWN
`AND RUNNING
`TOO FAST"
`RAMPING DOWN
`AND AT
`FULL SPEED
`
`'errur modes
`
`The conditions for generating the speed monitoring
`signals are selected to maximize safety so that when the
`status signals indicate error conditions, described fiir-
`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 change state, or change from low to
`high. If one of the signals does not change state at all
`during the monitoring period, then an error is 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 down to a
`stop, or is below the 0+ speed,
`then the Ramping-
`Downer-Stopped monitor signal is on, or has a high
`value. When this monitor signal is high, it indicates that
`the motor is slowing down or is almost stopped. If the
`actual deceleration of the motor when decelerating is
`too shallow or is 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 HO. 2.
`The Full-Speed monitor signal is on, or is set to a high
`value, when the actual motor speed is geater 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. When this
`signal is high, it indicates that the motor 14 is running at
`or above its full speed.
`is set
`The Forward/Normal«5peed monitor signal
`high when the motor speed 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. When this signal is high, it indicates that the
`motor 14 is running in a forward direction and is not
`running above its full speed.
`
`5
`ing to and from these speeds. The VFD changes motor
`speed when it receives the command signals from the
`ride control computer 20. The command signals, for
`example, can be 24-volt signals provided by contact
`switches.
`
`The upper part of FIG. 2 shows a typical motor speed
`profile for the motor 14. The speed profile illustrates the
`desired motor speed for a given elapsed time after an
`initial time T0. From an initially stopped condition at
`time T0, the motor is commanded to its full speed and
`therefore the motor speed ramps up from zero at time
`T0 to full speed at time T3. After a time interval of
`Operating at full speed, the motor is commanded to stop
`and therefore the motor speed ramps down from full
`speed at time T4 to motor stop at time TS. The preci-
`sion with which the control system 10 operates is illus—
`trated by the fact that the elapsed time from T4 to T8
`for motor deceleration is approximately one second.
`Error bounds are established for the speed of the
`motor 14 during the motor speed profile. The error
`bound for the full speed of the motor represents a range
`of acceptable speed above and below the full speed. The
`maximum acceptable full speed is designated in the
`FIG. 2 graph as "Full+" and the minimum acceptable
`full speed is designated as “Full—3’ 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 range is typically quite narrow.
`For example, if the frequency of pulse-width signals
`prostided by the VFD 12 is 60 Hz for the motor at full
`speed, then the maximum acceptable Full+ frequency
`is 62 Hz and the minimum acceptable Full— frequency
`is 53 Hz.
`
`The error bound for a motor 14 to be moving and still
`considered stopped is designated “0+” and is 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+ little] 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 bound indication 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 of the ride, 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/Normaia
`Speed monitor signal that are sent over signal lines 30,
`32, and 34, respectively. The following table shows the
`states of these three signals and their respective mean-
`mgs:
`
`S
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`4s
`
`50
`
`55
`
`65
`
`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
`from the tachometer 18, according to the signal that
`will be produced. For example, the Ramping~Down-or-
`Stopped monitor signal is determined by examining the
`velocity indicated from the tachometer as well as the
`rate of change of that velocity. In particular, if the
`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
`monitor signal is set high. If the mote:- veloeity is nega-
`tive, as is the case when the motor is running back-
`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-
`iug-Down-or-Stopped monitor signal is set high. The
`speed monitoring interface unit 16 will analyze the
`speed data in the sequence listed above to determine
`whether the Ramping-Dowrr-or—Stopped monitor sig-
`nal should be set high or low. Therefore, if the motor
`velocity is decreasing but is negative, then the Ramp-
`ing-Down-or-Stopped monitor signal will be pr0per1y
`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
`the motor 14 is 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
`high, even with noise on the Speed signal, untiI 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
`that the Ramping-Down—or—Stopped monitor signal is
`set low when the motor spwd is greater than 0+ at time
`T1 and is set high when ramping down beginning at
`time T4 through time T8.
`The speed monitoring interface unit 16 sets the Full-
`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
`the motor is 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
`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 motor is
`running in reverse, then the Forward/Normal-Speed
`monitor signal is set low.
`The ride control computer 20 operates according to a
`clock cycle and therefore receives updated signals at
`regular clock intervals. The ride control computer pro-
`duces four command signals in response to the three
`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
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`35
`
`65
`
`9
`
`5,349,276
`
`8
`command signals produced by the ride control com-
`puter are provided to the VFD 12 over signal lines 44.
`4-6, and 48, and comprise a Motor Run command signal,
`a Motor Speed command signal, and an Emergency
`Stop command signal, respectively.
`The Motor Run command signal is set high by the
`ride control computer 2!) whenever the ride control
`computer determines that the VFD 12 should operate
`the motor 14. This is determined by comparing the state
`of the ride and operator inputs against the Speed profile.
`The Motor Speed command signal selects the speed at
`which the motor will run. full speed or jog speed. The
`Motor Speed command signal is set high when the ride
`control computer wants the motor to run at full speed
`and is set low when it wants the motor to run at jog
`speed. The Emergency Stop command signal is set high
`at all times when the ride control computer determines
`that the motor 14 should be operated. The signal is low
`only when the ride control computer 2|] wants the VFD
`12 to perform an emergency deceleration to a complete
`stop. Finally, the Power Disconnect command signal 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 contactor is open and the motor 14 cannot
`run.
`
`The ride control computer 20 selects combinations of
`command signals and monitor signals, checks their sta—
`tus against expected values, and halts operation if dis-
`agreement persists beyond a 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
`command signals and monitor signals, there is a correct
`state. Whenever a command signal/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,
`i.e.,
`if a particular disagreement
`timer is allowed to run for a sufficient period so that it
`reaches a predetermined elapsed time, different for each
`timer, then the ride control computer 20 indicates a
`failure and initiates a failure response, usually it shut-
`down of the motor 14. The ride control computer resets
`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 disagreement timers.
`The first disagreement timer is 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 disagreement for the time it ordinarily takes
`the contactor 22 to close. The two signals are in dis-
`agreement, for example, when the Motor Run com—
`mand signal is high and the Contactor monitor signal is
`low. The second disagreement timer is a Failed-to-Stop
`timer, and is set to indicate a failure when the Motor
`Run command signal 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 time it ordinarily takes the contactor
`22 to Open. The next disagreement timer is the Failed-
`to-Run-Forward disagreement
`timer and indicates a
`
`

`

`9
`failure when the Motor Run command and Motor
`Speed command signals 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.
`The ride control computer 240 software implements a
`Failed-to-Run-Full-Speed disagreement timer that indi-
`cates a failure when the Motor Run command signal
`and Motor Speed command signal are high, the Full-
`Speed monitor signal is low, and the signals are in this
`condition for the time it ordinarily take; the motor 14 to
`ramp up to 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 timer indicates a fail-
`ure when the Full Speed monitor signal 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 command signal is
`high, the Motor Speed command signal is low, the
`Ramping—Down-or—Stopped monitor signal 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 disagreeth timer that indicates a failure
`when the Motor Run command signal, Full Speed com-
`mand signal, 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-
`tageou