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
`
`Related U.S. Application Data
`Division of Ser. No. 843,604, Feb. 28, 1992.
`62)
`51 Int. Cl.......................... H02P 5/00; HO2H 7/08;
`G01P 3/48
`52 U.S. C. .................................... 318/268; 318/434;
`318/464; 388/903; 388/909
`58) Field of Search ............... 318/565, 652, 653, 640,
`318/647, 463,254, 590, 602,618, 135, 138, 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
`Re. 32,857 2/1989 Luneau .
`1,438,616 12/1922 Staege.
`3,757,183 9/1973 Nola .
`3,916,272 10/1975 Grunleitner et al. .
`3,969,659 7/1976 Thode .
`4,078,189 3/1978 Nash et al. .
`4,208,621 6/1980 Hipkins et al. .
`
`(56)
`
`US005.349276A
`Patent Number:
`Date of Patent:
`
`11
`45
`
`5,349,276
`Sep. 20, 1994
`
`4,228,396 10/1980 Palombo et al. .
`4,292,577 9/1981 Cesarz et al. .
`4,305,025 12/1981 Arnold .
`4,386,398 5/1983 Matsuoka et al. .
`4,449,082 5/1984 Webster .
`4,492,902 1/1985 Ficken et al. .
`4,570,110 2/1986 Bloom et al. .
`4,572,999 2/1986 Coulon, Jr. .
`4,686,437 8/1987 Langley et al. .
`4,712,050 12/1987 Nagasawa et al. .
`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 Horbruegger et al. .
`Primary Examiner-Bentsu Ro
`Attorney, Agent, or Firm-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 elec
`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
`SPEED
`FORWARD/NORMAL MONITOR
`MONTORING
`FULL SPEED MONITOR 30
`RAMPING DOWN OR
`STOPPED MOTOR
`
`RIDE
`CONTROL
`COMPUTER
`(RCC)
`
`POWER DISCONNEC COMMAND 44
`MOTOR RUN COMMAND 4
`
`EMERGENCY STOP COMMAND
`
`
`
`
`
`
`
`
`
`1
`
`

`

`US. Patent
`
`Sep
`
`. 20, 1994
`
`Sheet 1 of 4
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`5,349,276
`
`ma:
`
`5528
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`@828
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`

`

`U.S. Patent
`
`Sep. 20, 1994
`
`Sheet 2 of 4
`
`5,349,276
`
`VELOCITY
`
`
`
`3
`
`

`

`U.S. Patent
`US. Patent
`
`Sep. 20, 1994
`Sep. 20, 1994
`
`Sheet 3 of 4
`Sheet 3 of 4
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`5,349,276
`5,349,276
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`mm
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`
` No—
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`4
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`

`

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

`

`1.
`
`CONTROL SYSTEM FOR REGULATING MOTOR
`SPEED
`
`5
`
`10
`
`15
`
`30
`
`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
`20
`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
`25
`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
`35
`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
`45
`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
`50
`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 down
`55
`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
`65
`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.
`
`5,349,276
`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 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 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
`
`6
`
`

`

`10
`
`15
`
`5,349,276
`3
`4.
`lished that are high when power should be applied to
`(VFD) that provides a sequence of drive signals to each
`the motor, when the motor should operate at full speed,
`phase of a motor 14 and a speed monitoring interface
`or when the motor should be stopped, and are low
`unit 16 that receives speed data from a tachometer 18
`and provides speed monitor signals to a ride control
`otherwise.
`Proper operation of the motor is indicated by the
`computer 20 that, in turn, provides motor command
`intersection of signal values. For example, if the mini
`signals to the VFD 12 to produce the desired drive
`mum full speed signal is high and the safe maximum
`signals and control the motor. The speed monitoring
`speed signal is low, then the motor is running over
`interface unit 16 monitors the motor speed received
`speed. If the VFD has been commanded to generate
`from the tachometer 18, compares it against a motor
`drive signals to operate the motor at full speed and the
`speed profile, and signals an error if there is a sufficient
`minimum full speed signal is low, then the motor has
`discrepancy. The ride control computer 20 checks for
`failed to reach full speed. To avoid false failure indica
`the occurrence of particular combinations of signal
`tions, each possible failure combination is assigned a
`values that are not expected if the motor 14 is properly
`following the speed profile. If an unexpected combina
`time limit. If a combination of signals indicates a failure,
`tion value persists beyond an acceptable time period
`then the condition must exist for at least the assigned
`time limit before operation will be halted. The time
`that depends on the particular combination, then the
`period for each failure combination is restarted each
`control system 10 indicates a failure and halts operation
`of the motor. In this way, the control system ensures
`time the error condition ceases.
`A motor control system in accordance with the in
`that the motor operates in accordance with the motor
`vention also advantageously determines the rotational
`speed profile and does not exceed a safe speed, deceler
`20
`speed and direction of the motor by using an electronic
`ates in a controlled, comfortable manner, and does not
`unexpectedly operate in reverse.
`tachometer that senses the current in at least two poles
`of the motor, removes the high-frequency components
`The motor 14 is used, for example, in an amusement
`of the sensed current signals, and provides a signal that
`park ride (not illustrated) and therefore safe, reliable
`indicates the fundamental frequency of the sensed cur
`operation is of extreme importance. The control system
`25
`rents and therefore the speed and direction of the mo
`10 increases the likelihood of safe operation by includ
`ing a three-phase output contactor 22, which acts as a
`tor. The motor speed can therefore be monitored and
`controlled electronically without the reliability and
`master on/off switch that can be opened to quickly
`maintenance problems associated with mechanical ta
`disconnect the motor 14 from the VFD 12 and allow
`chometers and with comparable accuracy. Such elec
`the ride vehicle to stop. The contactor 22 is closed by a
`30
`tronic speed determination is relatively simple to con
`combination of two signals, a command signal received
`struct and is easily integrated into the drive system of a
`from the ride control computer 20 over a power discon
`nect command line 24 and a power signal received from
`motor.
`The frequency of the sensed currents can be provided
`the VFD 12 over a contactor signal line 26. If either
`by current sensors attached to each one of the phase
`signal is absent, the contactor 22 will open. When the
`35
`leads attached to the motor. The sensed current signals
`contactor is closed, it allows drive signals from the
`can be filtered by a low-pass filter that removes substan
`VFD 12 to be provided to windings 13 of the motor,
`tially all frequency components greater than the maxi
`which define the motor poles and which create a mov
`mum expected operating speed. The pulsed signal that
`ing magnetic field that causes rotation of the rotor 15 of
`indicates the frequency of the filtered current signal can
`the motor. The contactor 22 produces a contactor mon
`be provided by a zero crossing detector that produces a
`itor signal that is high when the contactor is closed and
`low to high or high to low transition at each zero cross
`low when the contactor is open, and that is provided to
`ing of the filtered current signal. All of these compo
`the ride control computer 20 over a signal line 28.
`nents can be easily obtained and incorporated into a
`The tachometer 18 determines the speed of the motor
`motor control system.
`14 and provides this data to the speed monitoring inter
`45
`Other features and advantages of the present inven
`face unit 16. In the preferred embodiment, the tachome
`tion should be apparent from the following description
`ter is an electronic tachometer, which is described in
`of the preferred embodiments, which illustrate, by way
`greater detail below, but alternatively can be a conven
`of example, the principles of the invention.
`tional tachometer, such as a mechanical tachometer
`attached to the shaft of the rotor 15. The speed data
`BRIEF DESCRIPTION OF THE DRAWINGS
`from the electronic tachometer comprises a pulse train
`FIG. 1 is a block diagram of a motor control system
`that is provided to the speed monitoring interface unit
`constructed in accordance with the present invention.
`16, which compares the speed data against the motor
`FIG. 2 is a graph that shows a typical motor speed
`speed profile and produces three speed monitor signals
`profile for the motor illustrated in FIG. 1, along with
`that are either high or low depending on whether the
`the three status signals for the ride control computer.
`speed of the motor meets certain conditions. The sig
`FIG. 3 is a schematic diagram of an electronic ta
`nais, for example, can be 24-volt signals generated from
`chometer in accordance with the present invention, for
`contact switches.
`use with the motor control system illustrated in FIG. 1.
`The VFD 12 changes the speed of the motor 14 by
`FIG. 4 is a block diagram of a motor control system
`changing the cycle time of signals it provides to the
`constructed in accordance with the present invention
`motor. Typically, the VFD will provide two running
`speeds, full speed and jog speed. Full speed is the nor
`and applied to a linear motor.
`mal maximum running speed of the motor and jog speed
`DESCRIPTION OF THE PREFERRED
`is used to intermittently operate the motor and, for
`EMBODIMENTS
`example, park a ride vehicle. This allows the ride vehi
`65
`cle to be precisely positioned, such as during a parking
`With reference to FIG. 1, a motor control system 10
`constructed in accordance with the present invention
`maneuver. The VFD 12 provides the drive signals nec
`includes a variable frequency drive signal generator 12
`essary for commanding full speed, jog speed, and ramp
`
`50
`
`55
`
`7
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`

`15
`
`10
`
`5,349,276
`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.
`20
`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
`25
`FIG. 2 graph as "Full--' 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
`30
`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
`provided by the VFD 12 is 60 Hz for the motor at full
`speed, then the maximum acceptable Full-- frequency
`35
`is 62 Hz and the minimum acceptable Full-frequency
`is 58 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
`45
`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 bound indication will be
`50
`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
`55
`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/Normal
`Speed monitor signal that are sent over signal lines 30,
`65
`32, and 34, respectively. The following table shows the
`states of these three signals and their respective mean
`1ngs:
`
`SIGNAL 1
`SIGNAL 2 SIGNAL 3
`RAMP DOWN FULL FORWARD
`OR STOP
`SPEED NORMAL MEANING
`O
`O
`0.
`RUNNING IN
`REVERSE
`(REVERSE
`ERROR)*
`RUNNING
`BELOW FULL
`SPEED
`RUNNING TOO
`FAST
`(OVERSPEED
`ERROR)*
`RUNNING FULL
`SPEED
`STOPPEd
`RAMPING OOWN
`AND BELOW
`FULL SPEED
`RAMPING DOWN
`AND RUNNING
`TOO FAST
`RAMPING DOWN
`ANDAT
`FULL SPEED
`
`'error modes
`
`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 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
`Down-or-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 FIG. 2.
`The Full-Speed monitor signal is on, or is 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. When this
`signal is high, it indicates that the motor 14 is running at
`or above its full speed.
`The Forward/Normal-Speed monitor signal is set
`high when the motor speed is greater than the 0-value
`and less than the Full-l 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.
`
`8
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`5,349,276
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`8
`The speed monitoring interface unit 16 includes pro
`command signals produced by the ride control com
`gramming that is stored in non-volatile EPROM inte
`puter are provided to the VFD 12 over signal lines 44,
`grated circuits. The software in the speed monitoring
`46, and 48, and comprise a Motor Run command signal,
`interface unit generates these signals according to a
`a Motor Speed command signal, and an Emergency
`Stop command signal, respectively.
`precise methodology based on the information obtained
`from the tachometer 18, according to the signal that
`The Motor Run command signal is set high by the
`will be produced. For example, the Ramping-Down-or
`ride control computer 20 whenever the ride control
`Stopped monitor signal is determined by examining the
`computer determines that the VFD 12 should operate
`velocity indicated from the tachometer as well as the
`the motor 14. This is determined by comparing the state
`rate of change of that velocity. In particular, if the
`of the ride and operator inputs against the speed profile.
`velocity of the motor 14 is greater than or equal to an
`The Motor Speed command signal selects the speed at
`absolute stopped condition, and is less than or equal to
`which the motor will run, full speed or jog speed. The
`the 0-- level, then the Ramping-Down-or-Stopped
`Motor Speed command signal is set high when the ride
`monitor signal is set high. If the motor velocity is nega
`control computer wants the motor to run at full speed
`tive, as is the case when the motor is running back
`and is set low when it wants the motor to run at jog
`wards, the Ramping-Down-or-Stopped monitor signal
`speed. The Emergency Stop command signal is set high
`is set low. If the motor velocity is decreasing from any
`at all times when the ride control computer determines
`positive speed and is decreasing within the rates speci
`that the motor 14 should be operated. The signal is low
`fied by the Ramp- and Ramp-limits, then the Ramp
`only when the ride control computer 20 wants the VFD
`ing-Down-or-Stopped monitor signal is set high. The
`12 to perform an emergency deceleration to a complete
`speed monitoring interface unit 16 will analyze the
`stop. Finally, the Power Disconnect command signal is
`speed data in the sequence listed above to determine
`a fail-safe signal that closes the contactor 22 and enables
`whether the Ramping-Down-or-Stopped monitor sig
`the motor 14 to be driven by the VFD 12. If the signal
`nal should be set high or low. Therefore, if the motor
`is set low, the contactor is open and the motor 14 cannot
`velocity is decreasing but is negative, then the Ramp
`25
`1.
`ing-Down-or-Stopped monitor signal will be properly
`The ride control computer 20 selects combinations of
`command signals and monitor signals, checks their sta
`set low.
`Care is taken to provide a Ramping-Down-or
`tus against expected values, and halts operation if dis
`Stopped monitor signal whose output is steady. Thus,
`agreement persists beyond a set time period by generat
`the speed monitoring interface unit 16 ensures that, if 30
`ing the Power Disconnect command signal. The ride
`the motor 14 is at full speed, then the Ramping-Down
`control computer detects failure modes by using a pro
`or-Stopped signal will remain low, even if there is noise
`grammable logic controller that implements in soft
`on the speed signal from the tachometer 18. Moreover,
`ware, what are known to those skilled in the art as
`when the motor begins ramping down to a stop, the
`disagreement timers. In operation, at each point in the
`Ramping-Down-or-Stopped monitor signal remains
`motor speed profile graph in the upper portion of FIG.
`high, even with noise on the speed signal, until the
`2 and for various predetermined combinations of the
`motor speed reaches absolute zero. If the 0-- level is
`command signals and monitor signals, there is a correct
`above the jog speed level, then this monitor signal re
`state. Whenever a command signal/monitor signal com
`mains high while the motor runs at jog speed. This is
`bination is not in the correct state, they are said to dis
`illustrated in the lower portion of FIG. 2, which shows
`agree and the ride control computer 20 software will
`40
`that the Ramping-Down-or-Stopped monitor signal is
`keep track of the time during which there is disagree
`set low when the motor speed is greater than 0-- at time
`ment. If the time during which there is disagreement
`T1 and is set high when ramping down beginning at
`exceeds safe limits, i.e., if a particular disagreement
`time T4 through time T8.
`timer is allowed to run for a sufficient period so that it
`The speed monitoring interface unit 16 sets the Full
`reaches a predetermined elapsed time, different for each
`45
`Speed monitoring signal to a high value by examining
`timer, then the ride control computer 20 indicates a
`the velocity of the motor 14 as provided by the tachom
`failure and initiates a failure response, usually a shut
`eter 18. If the motor velocity is greater than or equal to
`down of the motor 14. The ride control computer resets
`the Full-level, then the Full-Speed monitoring signal
`the elapsed time for each disagreement timer to zero
`whenever a particular command signal/monitor signal
`is set high, and the signal is otherwise set low. Also, if 50
`the motor is running in reverse, the Full-Speed monitor
`combination is in the correct state, or is in agreement.
`ing signal is set low.
`In the preferred embodiment, the ride control com
`The speed monitoring interface unit 16 produces the
`puter 20 software implements nine disagreement timers.
`Forward/Normal-Speed monitor signal by examining
`The first disagreement timer is referred to as the Failed
`the velocity of the motor 14. If the motor velocity is
`to-Run timer and is set to indicate a failure when the
`55
`greater than or equal to the 0-- level and less than or
`Motor Run command signal and Contactor monitor
`signal are in disagreement for the time it ordinarily takes
`equal to the Full-- level, then the Forward/Normal
`Speed monitor signal is set high and otherwise is set
`the contactor 22 to close. The two signals are in dis
`low. Also, if the motor speed indicates the motor is
`agreement, for example, when the Motor Run com
`running in reverse, then the Forward/Normal-Speed
`mand signal is high and the Contactor monitor signal is
`60
`monitor signal is set low.
`low. The second disagreement timer is a Failed-to-Stop
`The ride control computer 20 operates according to a
`timer, and is set to indicate a failure when the Motor
`clock cycle and therefore receives updated signals at
`Run command signal is low and the Contactor monitor
`regular clock intervals. The ride control computer pro
`signal is high, and the signals are in this condition for
`duces four command signals in response to the three
`the time it ordinarily takes the motor 14 to stop from
`65
`status signals it receives from the speed monitoring
`full speed, plus the time it ordinarily takes the contactor
`interface unit 16 and in response to the Contactor moni
`22 to open. The next disagreement timer is the Failed
`tor signal it receives from the contactor 22. Three of the
`to-Run-Forward disagreement timer and indicates a
`
`35
`
`9
`
`

`

`10
`
`5,349,276
`10
`failure when the Motor Run command and Motor
`The drive signals produced by the VFD 12 are char
`Speed command signals are high and the Forward/Nor
`acterized by a great deal of noise, including high fre
`mal monitor signal is low, and are in this condition for
`quency transients. Each of the current sensors 66, 68,
`the time it ordinarily takes the motor to go from a
`and 70, which can be Hall-effect detectors, is coupled to
`stopped condition to the 0-- level.
`a stator wire 60, 62, and 64, respectively, that carries
`The ride control computer 20 software implements a
`current to one pole of the motor 14. The current signal
`Failed-to-Run-Full-Speed disagreement timer that indi
`is provided to the signal processing block 72, which
`produces a pulsed signal whose frequency corresponds
`cates a failure when the Motor Run command signal
`and Motor Speed command signal are high, the Full
`to the frequency of the changing current in the stator.
`Speed monitor signal is low, and the signals are in this
`The pulsed signal is provided via an output line 74 to an
`condition for the time it ordinarily takes the motor 14 to
`open collector transistor output 76 and to the speed
`ramp up to full speed. A Running-in-Reverse disagree
`monitoring interface unit 16.
`ment timer indicates a failure when the Ramping
`The speed monitoring interface unit 16 determines if
`Down-or-Stopped monitor signal, Full-Speed monitor
`the frequency of the speed signal, which corresponds to
`signal, and Forward/Normal-Speed monitor signal are
`the speed of the motor 14, is within a predetermined
`15
`all low and remain in that condition for the maximum
`range. For example, if the motor is used to drive an
`input update time for the ride control computer 20. A
`amusement park ride, the interface unit can determine if
`Run