Devices and Methods for Controlling a Railroad Crossing Gate Mechanism

Aspects of the present disclosure generally relate to railroad crossing gates and more particularly, to devices and methods for controlling a railroad crossing gate mechanism and associated gate arm(s).

Railroad crossing gates, which typically are raised by default and lowered when a train approaches and crosses an intersection of a road and railroad track (i.e., a crossing, also referred to as level crossing), are provided for roadway and pedestrian safety. In some instances, there may be separate gates for the roadway and the pedestrian path. For public safety reasons, it is essential that these crossing gates operate correctly.

Typically, railroad crossing gates utilize electrical and mechanical components to ensure that the gates perform their intended functions correctly. For example, gate arms are lowered using a motor located in a gate control mechanism. A crossing gate mechanism may be described as a gate control box housing multiple electric and electronic components for operating and controlling the signal control equipment and warning devices, such as the crossing gates. The gate control box includes a housing with a cover or door, so that the control box may be opened for maintenance or other services. The same mechanism uses or is connected to counterweights to counterbalance the gate arms during movement of the arms.

Per the American Railway Engineering and Maintenance-of-Way Association (AREMA), a crossing gate mechanism must lower and raise its gate arm(s) within a specified time limit. Further, the crossing gate mechanism should operate consistently over a wide operating voltage range, for example in different voltage environments in the U.S.A. and in Europe. To meet these different requirements, an improved gate control mechanism is desirable.

Briefly described, one or more embodiments of the present disclosure provide for a gate crossing mechanism, including techniques for controlling a gate crossing motor and crossing gate arm(s) associated with the gate crossing motor.

A first aspect of the present disclosure provides a crossing gate mechanism comprising a brushless direct current (BLDC) motor with at least one sensing device, a crossing gate arm operated via the BLDC motor, a control unit configured to control the BLDC motor to raise or lower the crossing gate arm in response to a gate control signal, wherein the control unit comprises position and speed proportional-integral-derivative (PID) controllers configured to output a pulse width modulation (PWM) command to a commutator logic, wherein the PWM command is converted to a motor direction and PWM duty cycle, and wherein the PWM duty cycle is variable depending on a motor input voltage.

A second aspect of the present disclosure provides a method for controlling a crossing gate mechanism, the method comprising measuring ascent time or descent time of a crossing gate arm, scaling a desired motor speed, receiving a gate control command to lower or raise the gate arm, sampling a motor input voltage, and creating a PWM command limit based on a sampled motor input voltage.

To facilitate an understanding of embodiments, principles, and features of the present disclosure, they are explained hereinafter with reference to implementation in illustrative embodiments. In particular, they are described in the context of devices or systems and methods for a crossing gate mechanism and controlling an arm of a crossing gate mechanism.

The components and materials described hereinafter as making up the various embodiments are intended to be illustrative and not restrictive. Many suitable components and materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of embodiments of the present disclosure.

A gate crossing mechanism protects motorists, pedestrians, and the like from oncoming trains by blocking level crossings or points at which public or private roads cross railway lines at the same level. As one example, a gate crossing mechanism can include an arm or “gate” that, using a motor, selectively lowers/raises depending upon whether a train or other vehicle is passing through the level crossing. For example, if a train is approaching a level crossing, a gate can be lowered to prevent traffic on the road or path from crossing the railway line. A level crossing can be equipped with multiple crossing mechanisms. For example, each side of the railway line can include a gate crossing mechanism. In larger intersections, each side of the railway line can include two (or more) gate crossing mechanisms. Gate crossing mechanisms can further include lights, sirens, bells, or other similar devices that can provide visual and/or aural warnings.

Conventional gate crossing mechanisms can be susceptible to failures, malfunctions, etc., which can reduce their reliability to control a level crossing safely. It is, therefore, desirable to improve efficiency and reliability of conventional gate crossing mechanisms. Gate crossing mechanisms having the features and functionality described herein improve efficiency and address problems associated with conventional gate crossing mechanisms.

illustrates a railroad crossing gatein a lowered or horizontal position. At many railroad crossings, at least one railroad crossing gatemay be placed on either side of the railroad track to restrict roadway traffic in both directions. At some crossings, pedestrian paths or sidewalks may run parallel to the roadway. To restrict road and sidewalk traffic, the illustrated railroad crossing gateincludes a separate roadway gateand pedestrian gate. The roadway gateand pedestrian gatemay be raised and lowered, i.e. operated, by gate control mechanism.

The example railroad crossing gatealso includes a poleand signal lights. The gate control mechanismis attached to the poleand is used to raise and lower the roadway and pedestrian gates,. The illustrated railroad crossing gateis often referred to as a combined crossing gate. When a train approaches the crossing, the railroad crossing gatemay provide a visual warning using the signal lights. The gate control mechanismwill lower the roadway gateand the pedestrian gateto respectively restrict traffic and pedestrians from crossing the track until the train has passed.

As shown in, the roadway gatecomprises a roadway gate support armthat attaches a roadway gate armto the gate control mechanism. Similarly, the pedestrian gatecomprises a pedestrian gate support armconnecting a pedestrian gate armto the gate control mechanism. When raised, the gatesandare positioned so that they do not interfere with either roadway or pedestrian traffic. This position is often referred to as the vertical position. A counterweightis connected to a counterweight support armconnected to the gate control mechanismto counterbalance the roadway gate arm. Although not shown, a long counterweight support arm could be provided in place of the short counterweight support arm.

Typically, the gates,are lowered from the vertical position using an electric motor contained within the gate control mechanism. The electric motor drives gearing connected to shafts (not shown) connected to the roadway gate support armand pedestrian gate support arm. The support arms,are usually driven part of the way down by the motor (e.g., somewhere between 70 and 45 degrees) and then gravity and momentum are allowed to bring the arms,and the support arms,to the horizontal position. In another example, the support arms,are driven all the way down to the horizontal position by the electric motor of the gate control mechanism.

illustrates a perspective view of crossing gate mechanismin accordance with an exemplary embodiment of the present disclosure.

The crossing gate mechanismcomprises an enclosurehousing multiple electric and electronic components, such as for example gearing, electric motordriving the gearing, and control unit. The control unitcomprises a printed circuit board (PCB)with the necessary electronics for operating and controlling the gate mechanismand associated crossing gate equipment, such as crossing gate arm(s), see for example. Further, the PCBcomprises for example display(s) and/or light emitting diodes (LEDs), used for example to indicate or display status of the gate mechanism, such status including for example ‘Power on’, ‘Gate Control’, ‘Brake On’, ‘Health’ etc.

The enclosurecan be opened and closed via door or cover, for maintenance, repair, or other services. The coveris moveable between a closed position and an open position, whereinshows the coverin the open position. The coveris closed via hingeand latch platein connection with a latch rod (not shown).

The electric motorincludes sensing devices, such as Hall effect sensors. The crossing gate arm(see) is operated via the electric motorand a controller, for example control unit, with at least one processor and control logic. The control unitis configured to control the electric motorto raise or lower the crossing gate armin response to a gate control input signal, provided for example by a gate control device. The gate control device provides gate control input signals, and can be for example a grade crossing controller, constant warning time device or another type of control equipment arranged wayside adjacent to a railroad track, for example in a crossing bungalow. When a gate control input signal is high, the gate armis being commanded to go up until it has reached a programmed, near-vertical gate-up position. When the gate control input signal is low, the gate armis being commanded to go down until it has reached a fixed, horizontal gate-down position.

illustrates a block diagram of a motor controller firmware design, including flow chart, for a control unit of a crossing gate mechanism in accordance with an exemplary embodiment of the present disclosure.

For example, with reference toand, control unitof gate mechanismfor controlling electric motorto raise or lower gate arms,can be designed to operate and/or perform functions as described herein.

In an example, a motor controller, for example control unit, is implemented as a field-programmable gate array (FPGA), which is selected for its real-time responsiveness and ability to handle multiple activities at once. In other examples, the motor controller is designed or implemented in a real-time central processing unit (CPU), an application-specific integrated circuit (ASIC), a complex programmable logic device (CPLD) or a system-on-chip (SoC). In case of a SoC, the SoC comprises a CPU and an FPGA.

In an embodiment, the electric motor(see), controlled and/or operated by the control unit, is an electric brushless direct current motor, herein referred to as BLDC motor, with at least one sensing device. For example, the electric BLDC motor can be a 10-pole BLDC motor with three (3) Hall effect sensors. However, it should be noted that the electric motormay be another type of electric motor, such as a brushed DC motor or other type of DC- or AC-motor. Further, the at least one sensing device may be another type of sensor(s) that can detect position and direction (speed) of the electric motor.

In an exemplary embodiment of the present disclosure and with reference to, Hall UVWare Hall effect sensor input signals received from the BLDC motor, specifically the Hall effect sensors installed in the BLDC motor. The Hall UVWsensor input signals are debounced, by Hall UVW Debounce, to minimize extraneous edge detections.

A Hall State Encoderdetermines a current Hall State as well as a motor direction of the BLDC motor. In an example, the Hall effect sensor input signals are received as a sequence represented by vector <U V W>, where U is the most significant bit and W is the least significant bit. The sequence is encoded into the Hall State. When the Hall State is received in a first order, the Hall State Encoderindicates that the BLDC motor is turning in a forward direction, which for Position Estimatorresults in an actual position of the gate arm, measured in Hall-state units, counting upward. When the Hall State is received in a second order, then the Hall State Encoderindicates that the BLDC motor is turning in a reverse direction, which for the Position Estimatorresults in the actual position of the gate arm, measured in Hall-state units, counting downward. Further, the Hall State is also used by a commutation block, see Commutator, to determine a correct firing sequence for motor phases A, B and C of the BLDC motor.

As noted, the Position Estimatordetermines the actual position of the gate arm by counting the number of Hall States that have been received from the Hall State Encoder. A Hall State received in a forward direction, results in the actual position being incremented by one; a Hall State received in a reverse direction, results in the actual position being decremented by one. Forward and reverse directions are determined by the Hall State Encoder. When the gate arm is moving up, the actual position is counting up in a forward direction; when the gate arm is moving down, the actual position is counting down in a reverse direction. For an entrance gate, each time the arm reaches the bottom, unless an obstruction in the downward direction has been encountered, the actual position is reset to avoid accumulating any positional error.

An actual speed generated by Speed Estimatoris a count of the number of Hall States that have been sent by the Hall State Encoderduring a sampling window in a given direction, multiplied by a scaling factor that converts the count to motor revolutions per second (RPS).

Gate Control, referred to as GC, comprises and provides gate control input signals, received from a grade crossing controller, constant warning time device or other type of control equipment arranged wayside adjacent to a railroad track, for example in a crossing bungalow. For an entrance gate, when GCis high, the gate arm is being commanded to go up until it has reached a programmed, near-vertical gate-up position. When GCis low, the gate arm is being commanded to go down until it has reached a fixed, horizontal gate-down position. For an exit gate, it is the reverse: when GCis high, the gate arm is commanded to go down, and when GCis low, the gate arm is commanded to go up.

Typically, crossing gates are either configured as an entrance gate or an exit gate. An entrance gate is installed on the vehicle entry side of a railroad crossing zone, wherein an exit gate is installed on the vehicle exit side of the crossing zone. The exit gates can be equipped with a delay and begin their descent to their horizontal position several seconds after the entrance gates do, to avoid trapping vehicles in the crossing zone. Whether or not a gate is an entrance or exit gate is part of the Gate Configuration input to the Gate Control State Machine. As noted, the exit gate first delays lowering the arm to allow exit of a vehicle in the process of crossing, then later lowers the arm to prevent reverse entry of a vehicle into a crossing. The two GC signals to the entrance and exit gates are not the same signal and happen at different times. A reason the GC signals are opposite state for entrance and exit gate is that if both GC signals drop out due to some fault at the bungalow and therefore both GC signals go low, then the fail-safe position of an entrance gate is to lower its arm (to prevent a vehicle from entering a crossing), whereas for an exit gate, the fail-safe position is to raise its arm (to allow a vehicle to exit a crossing).

The input signal from GCis debounced, by GC Debounce, to minimize extraneous edge detections. Gate Control State Machinereceives a debounced GC input signal to determine a proper motion of the gate arm. The Gate Control State Machinedetermines or decides whether the gate arm needs to move up, move down or stop moving to achieve a desired position for the gate arm. The Gate Control State Machinealso manages states of multiple outputs, including motor brake and motor snub circuit.

A Position PID (proportional-integral-derivative) Controllercompares the actual position, provided by Position Estimator, to the desired position, provided by the Gate Control State Machine, of the gate arm and outputs a desired speed/velocity. A scaling factor can also be applied to the desired speed to slow down or speed up the arm movement.

A Speed PID (proportional-integral-derivative) Controllercompares the actual speed to the desired speed of the gate arm and outputs a PWM (pulse width modulation) command. In an example, the Position PID Controlleruses a PID control loop to meet a desired position by outputting a desired velocity to the Speed PID Controller.

A Scale Desired Speed logicmultiplies the desired speed/velocity by an ascent or descent speed scale factor, depending on whether the gate arm is moving up or moving down, respectively. The ascent or descent speed scale factors are initialized by a processor of the gate control mechanism and automatically adjusted within a constrained range to better meet the desired up-time or desired down-time, as programmed by the processor into the motor controller.

The Speed PID Controlleruses for example a PID control loop to meet a scaled desired velocity by outputting a PWM command to the Commutator. The PWM command from the Speed PID Controlleris converted into a motor direction and PWM duty cycle, which the Commutatoruses, along with the encoded Hall State, to activate half-bridge field effect transistors (FETs) that deliver current to a sequence of motor winding phases, such as phases A, B, C. To cause the BLDC motor to spin, the three motor winding phases A, B and C are energized by the Commutatorin a rotating sequence. The Hall State from the Hall State Encoderindicates the current motor position, based on which corresponding windings are energized. The Commutatorcan further be configured to provide reverse commutation to spin the BLDC motor in an opposite direction, thus causing the gate arm to move both up and down.

In an embodiment, a method for driving or operating the BLDC motor is a complementary pulse width modulation (PWM) using six independently controlled FETs (a high and low FET for each motor phase). As each phase A, B, C is being driven the high and low side FETs will be driven inversely, with a guaranteed “dead time” where neither the high FET nor the low FET is driven.

As noted earlier, per AREMA, a crossing gate mechanism must lower and raise its gate arm(s) within a specified time limit. More specifically, a crossing gate mechanism must lower its gate arm within 10-15 seconds and raise its gate arm within 12 seconds. This must be done over a normal operating voltage range. It is desirable to do so also under normal and adverse weather conditions; for example, when it is very cold and there is ice buildup on the gate arm, or when it is very hot, and the electric motor is less efficient.

Further, the crossing gate mechanism should operate consistently over a wide operating voltage range, for example in different voltage environments in the U.S.A. and in Europe. For example, a gate mechanism must operate consistently over 9V-18V in a 12V environment (i.e., USA) and over 18V-36V in a 24V environment (i.e., Europe). With respect to a BLDC motor, its motor speed is directly affected by the voltage applied to it.

In accordance with an exemplary embodiment of the present disclosure and with respect to the required ascent and descent times, the Scale Desired Speed logiccomprises a closed-loop control for measuring ascent time and descent time of the crossing gate arm, in response to received desired ascent time and descent time as inputs. By implementing a closed-loop control, the descent time can be measured, which provides feedback to the control logicto raise or lower the arm speed to achieve the desired descent time. Likewise, the same can occur for the ascent time. This avoids having to set a resistor value and measuring the time that results; instead, the installer or user can now simply request a specific ascent or descent time, within the AREMA requirements, and that desired time will be met by the closed-loop control system. As a result, the ascent and descent times can be configured digitally and does not need any further set up by the installer. It is not necessary to set a resistor value and determine if such a resistor setting results in the desired descent time. The ascent and descent times will be maintained by the gate-mechanism's closed-loop control system from that point forward, without further intervention by the installer.

With respect to a wide operating voltage range, an in accordance with another exemplary embodiment of the present disclosure, an algorithm is provided and implemented which involves selective sampling of an input voltage and scaling a maximum current to the BLDC motor accordingly to maintain smooth control of the gate arm. Motor Voltageincludes an input voltage level for the electric motor and gate mechanism. Such input voltage level is set for example by an operator or user of the gate mechanism. The gate mechanism and electric motor may be operated at 24V or may be operated at 12V, depending on a voltage environment. The motor voltageis input to an analog-to-digital converter, which then provides a motor voltage sample to the Scale Desired Speed logic. Based on the motor voltage sample (input voltage level, motor voltage), the logicissues a PWM command limit, which sets up a maximum current for the respective voltage sample. The PWM command limit is sent to the Speed PID Controllerthat outputs PWM commands, including commanded motor direction (clockwise or counterclockwise) and the PWM duty cycle.

The PWM duty cycle is delivered to the commutator logicto command a specific level of current to the BLDC motor. Setting a maximum for the PWM duty cycle has an effect of setting a maximum on the commanded motor current for a given input voltage to the motor, which is sampled just prior to moving the gate arm. By setting a maximum current, the motor control system will be given proper bounds within which to achieve the desired ascend and descend times of the gate arm.

By limiting the PWM command and therefore setting the maximum current, detecting obstruction of the gate arm is also improved. This is implemented by Detect Obstruction logic. For example, approaching a maximum current due to obstruction when the input voltage is 36V would occur at about half the current level than when the input voltage is 18V. By lowering the maximum current by nearly 50% from the 18V setting, the motor control system can detect obstruction more readily when the input voltage is 36V. For example, by comparing a desired position to an actual position and a desired speed to an actual speed of the gate arm (utilizing Position PID Controllerand Speed PID controller), the Gate Control State Machinecan determine an obstruction/hindrance of the gate arm, based on discrepancies of position/speed and direction of motion.

illustrates a tableincluding maximum motor current over input voltage range for a brushless electric motor of a crossing gate mechanism in accordance with an exemplary embodiment of the present disclosure.

The PWM command from the Speed PID controlleris converted into a commanded motor direction and PWM duty cycle, which the commutator logic uses along with the encoded Hall State to activate half-bridge FETs that deliver current to a sequence of motor winding phases. A maximum permissible PWM duty cycle for different input voltages is shown in the table. For example, when motor input voltage is less than 11V, the maximum PWM duty cycle is 90% duty cycle. On the other hand, when the motor voltage is equal or greater than 34V, the maximum PWM duty cycle is 28% duty cycle. By staying within these maximum PWM duty cycle limits at the referenced voltages, the desired ascent and descent times are achieved while still allowing for detection of obstruction when the maximum PWM duty cycle is approached.illustrates a flow chart of a methodfor controlling a crossing gate mechanism in accordance with an exemplary embodiment of the present disclosure. The methodmay be performed utilizing a crossing gate mechanism with a control unit and corresponding firmware as described with reference to.

While the method is described as a series of acts or steps that are performed in a sequence, it is to be understood that the method may not be limited by the order of the sequence. For instance, unless stated otherwise, some acts may occur in a different order than what is described herein. In addition, in some cases, an act may occur concurrently with another act. Furthermore, in some instances, not all acts may be required to implement a methodology described herein.

The method may start at. The methodcomprises measuring ascent time or descent time of the gate arm (act) and scaling a desired motor speed (act). In act, a gate control command to lower or raise the gate arm is received (from Gate Control), and a motor input voltage (from Motor Voltage) is sampled (act). Based on the sampled motor input voltage, a PWM Command Limit is created (act) and a PWM Command generated (act), using PID control systems, such as Speed PID Controller. In act(decision block), the PID control systems examine whether the generated PWM Command is greater than the created PWM Command Limit. If the PWM Command is not greater than the PWM Command Limit, no changes are necessary, and the systems continue with the generated PWM Command (act). If the PWM Command is greater than the PWM Command Limit, the control systems are configured to limit the PWM Command in accordance with the PWM Command Limit (act). Based on the PWM Command, the control systems, for example using Commutator logic, commutate drive signals to the BLDC motor to lower or raise the gate arm (act). The methodis repeated, starting at act.

As described, the methodcomprises a closed-loop control by incorporating measuring ascent time and descent time of the crossing gate arm. Further, the methodcomprises detecting an obstruction of the crossing gate arm based on the PWM command limit, the PWM command and an actual velocity of the crossing gate arm; generating an error code in response to a detected obstruction; and halting operation of the crossing gate arm in response to a detected obstruction.

Further, a non-transitory computer readable medium storing executable instructions, which, when executed by a computer, perform the method for controlling a railroad crossing gate mechanism as described is provided.