Aircraft brake system

A braking system is disclosed. In various embodiments, the braking system includes a brake stack; an actuator configured to apply a compressive load to the brake stack; a servo valve coupled to a power source and to the actuator; and a brake control unit configured to operate the servo valve at a current ramp rate in response to a pedal deflection signal, wherein the current ramp rate is determined via a relationship between the current ramp rate and a brake pressure command signal.

FIELD

The present disclosure relates to aircraft wheel and brake systems and, more particularly, to systems and methods for reducing the effect of brake fill following a brake activation.

BACKGROUND

Aircraft typically utilize brake systems on wheels to slow or stop the aircraft during landings, taxiing and emergency situations, such as, for example, a rejected takeoff (RTO), which generally refers to engagement of a brake system during an aborted takeoff and involves high braking loads over a short time period, resulting in a rapid increase in the brake temperature. The brake systems generally employ a heat sink comprising a series of friction disks, sandwiched between a pressure plate and an end plate, that may be forced into sliding contact with one another during a brake application to slow or stop the aircraft. A typical hydraulic brake system may include, without limitation, a source of pressurized hydraulic fluid, an actuator for exerting a force across the heat sink (e.g., across the pressure plate, the series of friction disks and the end plate), a valve for controlling a pressure level provided to the actuator and a brake control unit for receiving inputs from an operator and from various feedback mechanisms and for producing responsive outputs to the valve.

Upon activation of the brake system (e.g., by depressing a brake pedal), a pressurized fluid is applied to the actuator, which may comprise a piston configured to translate the pressure plate toward the end plate. Typically, there will, however, be some displacement of the brake components (e.g., translation of the piston and the various components of the heat sink) prior to a force being established across the components of the heat sink, at which point a brake force is exerted against the wheels to slow the aircraft. Consequently, a measured pressure level at the actuator and used for feedback to the brake control unit may be very low for a period of time until the force is actually established across the heat sink. As a result, there may exist a short period of time or a lag following activation of the brake system where a brake command signal output by the brake control unit does not generate an actual brake engagement.

The condition just described is sometimes referred to as brake fill. During the lag associated with brake fill, the brake control unit may instruct the valve (e.g., via a brake command signal) to open further in order to generate an actual brake engagement (e.g., a slowing torque applied to a wheel). This may occur, for example, if the brake control unit includes an integrator that accumulates the product of error and time. As time passes without error reduction (or without feedback indicating an actual brake engagement), the brake control unit may continue to increase the level of the brake command signal being output to the valve, thereby increasing the pressure level to the actuator. Once the force is finally established across the heat sink, an actual brake engagement will occur, but such will be in response to the increased brake command signal. The increased brake command signal is the result of the accumulated error during the brake fill condition and typically results in greater braking than is desired until the brake control unit recovers and outputs a reduced brake command signal more representative of a desired or input level of braking. Brake fill may thus result in unwanted grabbing or jerky brake performance and may be present with any type of braking system (e.g., hydraulic, pneumatic or electromechanical).

SUMMARY

A braking system is disclosed. In various embodiments, the braking system includes a brake stack; an actuator configured to apply a compressive load to the brake stack; a servo valve coupled to a power source and to the actuator; and a brake control unit configured to operate the servo valve at a current ramp rate in response to a pedal deflection signal, wherein the current ramp rate is determined via a relationship between the current ramp rate and a brake pressure command signal.

In various embodiments, the relationship provides distinct values for the current ramp rate on a curve of the current ramp rate versus the brake pressure command signal. In various embodiments, the curve of the current ramp rate versus the brake pressure command signal includes a smoothly varying function. In various embodiments, the curve of the current ramp rate versus the brake pressure command signal includes a step function. In various embodiments, the curve of the current ramp rate versus the brake pressure command signal includes a constant slope function.

In various embodiments, the pedal deflection signal is generated by a transducer connected to a brake pedal. In various embodiments, the current ramp rate corresponds with the brake pressure command signal generated by the brake control unit. In various embodiments, the pedal deflection signal is generated by the transducer connected to the brake pedal and the brake control unit is configured to convert the pedal deflection signal to the brake pressure command signal.

In various embodiments, a pressure sensor is coupled to the actuator and configured to provide a feedback signal to the brake control unit. In various embodiments, the power source is at least one of a hydraulic power source, an electric power source and a pneumatic power source. In various embodiments, the power source is a hydraulic power source.

A method of operating a braking system is disclosed. In various embodiments, the method includes generating a pedal deflection signal via a brake pedal; providing the pedal deflection signal to a brake control unit; determining by the brake control unit a brake pressure command signal based on the pedal deflection signal; and determining by the brake control unit an output current configured to operate a servo valve coupled to a brake actuator and to a power source, wherein the output current is increased at a current ramp rate based on the brake pressure command signal.

In various embodiments, the current ramp rate is determined via a relationship between the current ramp rate and the brake pressure command signal. In various embodiments, the relationship provides distinct values for the current ramp rate on a curve of the current ramp rate versus the brake pressure command signal.

In various embodiments, the pedal deflection signal is generated by a transducer connected to the brake pedal in response to a brake pedal deflection. In various embodiments, the pedal deflection signal is one of a first pedal deflection signal or a second pedal deflection signal generated by the transducer connected to the brake pedal in response to a first brake pedal deflection or a second brake pedal deflection and wherein the current ramp rate corresponds with one of a first brake pressure command signal or a second brake pressure command signal generated by the brake control unit in response to the first brake pedal deflection or the second brake pedal deflection.

In various embodiments, a pressure sensor is coupled to the brake actuator and configured to provide a feedback signal to the brake control unit. In various embodiments, the power source is a hydraulic power source.

A brake control unit, comprising a tangible, non-transitory memory and a processor is disclosed. In various embodiments, the brake control unit includes instructions stored thereon that, in response to execution by the processor, cause the brake control unit to perform a series of operations, including receiving a pedal deflection signal generated in response to a deflection of a brake pedal; determining a brake pressure command signal based on the pedal deflection signal; and determining an output current configured to operate a servo valve coupled to a brake actuator and to a power source, wherein the output current is increased at a current ramp rate based on the brake pressure command signal. In various embodiments, the current ramp rate is determined via a relationship between the current ramp rate and the brake pressure command signal, the relationship providing distinct values for the current ramp rate on a curve of the current ramp rate versus the brake pressure command signal.

DETAILED DESCRIPTION

Referring now toFIG.1A, an aircraft100includes multiple landing gear systems, including a first landing gear102, a second landing gear104and a third landing gear106. The first landing gear102, the second landing gear104and the third landing gear106each include one or more wheel assemblies. For example, the third landing gear106includes an inner wheel assembly108and an outer wheel assembly110. The first landing gear102, the second landing gear104and the third landing gear106support the aircraft100when the aircraft100is not flying, thereby enabling the aircraft100to take off, land and taxi without damaging the aircraft100. In various embodiments, the second landing gear104is a nose landing gear for the aircraft100and, oftentimes, one or more of the first landing gear102, the second landing gear104and the third landing gear106are operationally retractable into the aircraft100when the aircraft100is in flight or airborne.

In various embodiments, the aircraft100further includes an avionics unit112, which includes one or more controllers (e.g., processors) and one or more tangible, non-transitory memories capable of implementing digital or programmatic logic. In various embodiments, for example, the one or more controllers are one or more of a general purpose processor, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate array (FPGA) or other programmable logic device, discrete gate, transistor logic, or discrete hardware components, or any various combinations thereof or the like. In various embodiments, the avionics unit112controls operation of various components of the aircraft100. For example, the avionics unit112controls various parameters of flight, such as an air traffic management systems, auto-pilot systems, auto-thrust systems, crew alerting systems, electrical systems, electronic checklist systems, electronic flight bag systems, engine systems flight control systems, environmental systems, hydraulics systems, lighting systems, pneumatics systems, traffic avoidance systems, trim systems and the like.

In various embodiments, the aircraft100further includes a brake control unit (BCU)120. With brief reference now toFIG.1B, the BCU120includes one or more controllers115(e.g., processors) and one or more memories116(e.g., tangible, non-transitory memories) capable of implementing digital or programmatic logic. In various embodiments, for example, the one or more controllers115are one or more of a general purpose processor, DSP, ASIC, FPGA, or other programmable logic device, discrete gate, transistor logic, or discrete hardware components, or any various combinations thereof or the like, and the one or more memories116store instructions that are implemented by the one or more controllers115for performing various functions, such as adjusting the hydraulic pressure provided to a brake actuator depending on the degree of braking desired, as will be discussed herein. In various embodiments, the BCU120controls the braking of the aircraft100. For example, the BCU120controls various parameters of braking, such as manual brake control, automatic brake control, antiskid braking, locked wheel protection, touchdown protection, emergency/park brake monitoring or gear retraction braking. The BCU120may further include hardware117capable of performing various logic using discreet power signals received from various aircraft systems. Referring again toFIG.1A, the aircraft100further includes one or more brakes coupled to each wheel assembly. For example, a brake118is coupled to the outer wheel assembly110of the third landing gear106of the aircraft100. During operation, the brake118applies a braking force to the outer wheel assembly110upon receiving a brake command from the BCU120. In various embodiments, the outer wheel assembly110of the third landing gear106of the aircraft100comprises any number of wheels or brakes.

Referring now toFIG.2, a braking system200is illustrated, in accordance with various embodiments. The braking system200includes a brake control unit (BCU)220, similar to the BCU120described above with reference toFIGS.1A and1B, which is programmed to control the various braking functions described herein. In various embodiments, the braking system200enables an aircraft to brake, thereby slowing or stopping the aircraft when landing or taxiing on the ground. However, it will be appreciated that the braking system200may also be used in connection with other types of vehicles without departing from the scope of the disclosure.

As described herein, the braking system200generally includes a hydraulic power source225acting through a left servo valve230to apply hydraulic pressure through a left hydraulic line231to apply a braking force to a left actuator234(or to a plurality of left actuators) of a left wheel and brake assembly235. Similarly, the braking system200includes a right servo valve250configured to apply hydraulic pressure through a right hydraulic line251to apply a braking force to a right actuator254(or to a plurality of right actuators) of a right wheel and brake assembly255. A left pressure sensor233may be positioned in fluid communication with the left actuator234of the left wheel and brake assembly235and a right pressure sensor253may be positioned in fluid communication with the right actuator254of the right wheel and brake assembly255. In various embodiments, the left pressure sensor233and the right pressure sensor253(each comprising a pressure sensor) and the left actuator234and the right actuator254(each comprising an actuator) may be common to both a primary braking system and a non-primary braking system that exist within the braking system200. Further, while the disclosure makes general reference to left and right sides of a braking system, it will be appreciated that the disclosure is applicable to any number of wheel and brake assemblies (e.g., first, second and third wheel and brake assemblies) as well as to inboard and outboard wheel and brake assemblies.

During operation, the BCU220receives brake command signals from a left pilot brake pedal236and a right pilot brake pedal256or a left co-pilot brake pedal237and a right co-pilot brake pedal257. The brake command signals from the left pilot brake pedal236and the right pilot brake pedal256or from the left co-pilot brake pedal237and the right co-pilot brake pedal257are indicative of a desired amount of braking. In addition, the BCU220receives control signals from an auto-brake interface226for performing auto-brake and rejected take-off (RTO) braking functions. The BCU220also receives a series of discrete control signals associated with the aircraft, generally represented as aircraft discretes227, for providing braking control thereof. In various embodiments, the braking system200further includes an output device223(e.g., a display) coupled to the BCU220. The output device223is configured to communicate information to the pilot or the co-pilot or to maintenance crew relating to the braking operations. For example, in various embodiments, the output device223includes a gauge, a speaker or a network access communication port configured to provide a message to a remote terminal. In various embodiments, the BCU220controls the output device223to output a health status of the braking system200or the various components thereof.

In various embodiments, the BCU220controls braking of the left wheel and brake assembly235and the right wheel and brake assembly255, as noted above. The left wheel and brake assembly235includes a left wheel238(or a plurality of left wheels) and a left brake stack239(or a plurality of left brake stacks). The left actuator234(or a plurality of left actuators) may be provided for exerting a braking force (e.g., a compressive load) on the left brake stack239in order to brake the left wheel238. Similarly, the right wheel and brake assembly255includes a right wheel258(or a plurality of right wheels) and a right brake stack259(or a plurality of right brake stacks). The right actuator254(or a plurality of right actuators) may be provided for exerting a braking force (e.g., a compressive load) on the right brake stack259in order to brake the right wheel258. In various embodiments, the left wheel and brake assembly235and the right wheel and brake assembly255also include, respectively, a left wheel speed sensor240and a right wheel speed sensor260, that provide wheel speed information to the BCU220for carrying out brake control operations.

In various embodiments of the braking system200, the hydraulic power source225serves as a primary brake power supply within the braking system200. In various embodiments, a primary hydraulic line270is connected to the hydraulic power source225via a check valve271and is also connected to an accumulator272. In various embodiments, the primary hydraulic line270is input to a brake control module (BCM)275that is also comprised within the braking system200. The BCM275includes a shutoff valve273through which the primary hydraulic line270supplies hydraulic fluid to the left servo valve230and the right servo valve250. In this regard, the BCM275may be a dual valve assembly. In various embodiments, hydraulic fluid from the left servo valve230and the right servo valve250is, respectively, provided through the left hydraulic line231and the right hydraulic line251to apply the braking force to the left wheel238and the right wheel258during a braking operation.

During a braking operation, pressurized hydraulic fluid passes through the left hydraulic line231and the right hydraulic line251to the left actuator234and the right actuator254, respectively. The shutoff valve273is open to the left hydraulic line231and the right hydraulic line251, and the BCU220controls the level of hydraulic pressure that is delivered to the wheels via the left servo valve230and the right servo valve250acting through the left hydraulic line231and the right hydraulic line251. In various embodiments, the shutoff valve273, the left servo valve230and the right servo valve250are coil valves. In various embodiments, the shutoff valve273receives a shutoff valve control signal on a bus276from the BCU220. Similarly, the left servo valve230may receive a left servo valve control signal on a left bus277from the BCU220and the right servo valve250may receive a right servo valve control signal on a right bus278from the BCU220. The braking system200utilizes the shutoff valve273in-line with the left servo valve230and the right servo valve250to provide a level of redundancy that ensures a single valve failure cannot cause inadvertent braking. In order for the braking force to be applied by the braking system200to the left wheel and brake assembly235and the right wheel and brake assembly255, the shutoff valve273is open along with at least one of the left servo valve230and the right servo valve250. To provide a redundancy so that the brakes can be operated when commanded, each of the valves (shutoff and servo) may contain dual control coils with one coil for different dedicated channels in the BCU220.

In various embodiments, the left pilot brake pedal236(or the left co-pilot brake pedal237) provides a pedal deflection signal to the BCU220that is indicative of a degree of travel of the left pilot brake pedal236(or the left co-pilot brake pedal237) and the amount of desired braking by the left wheel and brake assembly235. In response to the pedal deflection signal, the BCU220generates the left servo valve control signal to be received by the left servo valve230. The left servo valve control signal is then used by the left servo valve230to control the amount of hydraulic pressure that is applied to the left actuator234. Similarly, the right pilot brake pedal256(or the right co-pilot brake pedal257) may provide a pedal deflection signal to the BCU220that is indicative of a degree of travel of the right pilot brake pedal256(or the right co-pilot brake pedal257) and the amount of desired braking by the right wheel and brake assembly255. In response to the pedal deflection signal, the BCU220generates the right servo valve control signal to be received by the right servo valve250. The right servo valve control signal is then used by the right servo valve250to control the amount of hydraulic pressure that is applied to the right actuator254. In various embodiments, each brake pedal may have a corresponding transducer configured to provide the pedal deflection signal to the BCU220. In various embodiments, the braking system200includes the left pressure sensor233for monitoring the hydraulic pressure in the left hydraulic line231and in the left actuator234and the right pressure sensor253for monitoring the hydraulic pressure in the right hydraulic line251and in the right actuator254. As illustrated, the left pressure sensor233is configured to provide a feedback signal to the BCU220via a left pressure signal bus241and the right pressure sensor253is configured to provide a feedback signal to the BCU220via a right pressure signal bus261. In addition, power to the BCU220is provided from an aircraft power source221, such as, for example, a 28-Volt DC power source within the aircraft.

With continued reference toFIG.2, the brake fill condition described above may be illustrated. For purposes of generality, the left side of the braking system200is used to describe the condition. Upon activation of the left pilot brake pedal236(or a brake pedal), a pedal deflection signal is generated by a transducer222coupled to the left pilot brake pedal236and directed to the BCU220. As described above, the pedal deflection signal reflects a degree of travel (or a percentage deflection) of the brake pedal. The BCU220then generates a brake pressure command signal based on the pedal deflection signal. At the same time, the BCU220opens the shutoff valve273and provides an initial signal (e.g., an initial current level) to the left servo valve230. The left servo valve230then activates and opens an amount sufficient to provide hydraulic fluid to the left actuator234at a rate that corresponds to the initial signal or the initial current level. Following the initial opening of the left servo valve230according to the initial current level, the BCU220steadily increases the current provided to the left servo valve230at a current ramp rate corresponding to the brake pressure command signal (see, e.g.,FIG.4). A measured pressure signal is generated by the left pressure sensor233and directed as feedback to the BCU220. During the period of time when the left actuator234is filling with hydraulic fluid or the left brake stack239is translating toward engagement (i.e., the brake fill period or lag), the measured pressure signal will be low and likely significantly below the pressure corresponding with the pedal deflection signal or the brake pressure command signal. The BCU220will continue increasing the current level provided to the left servo valve230until a contact pressure threshold (e.g., 200 psi or ≈1400 kPa) is reached, where the contact pressure threshold is indicative of the actuator having engaged the brake stack (i.e., the end of the brake fill period or lag). Once the left pressure sensor233informs the BCU220that the brake pressure has reached the contact pressure threshold, the BCU220stops the steady increase of current provided to the left servo valve230and switches to a pressure control mode. It is during this mode switching—e.g., from a brake fill mode to a pressure control mode—that an overshoot in brake pressure occurs, leading to the unwanted grabbing or jerky brake performance described above.

Referring now toFIGS.3A and3B, a pair of graphs300are provided that illustrate the effect of current ramp rate on brake fill overshoot.FIG.3Arepresents an aggressive fill situation and an aggressive brake fill overshoot302, where the current ramp rate received by a servo valve, such as, for example, the left servo valve230described above is high, relative to a gentle fill situation and a gentle brake fill overshoot304depicted inFIG.3B. Generally speaking, the greater the rate at which the actuator is filled with hydraulic fluid, the more severe the grabbing or jerkiness on brake performance (e.g., the brake fill overshoot) at the termination of the brake fill. Referring toFIG.3A, for example, as the brake pedal is deflected, typically there is no braking between zero percent (0%) and fifteen percent (15%) of pedal deflection. Once the pedal deflection exceeds 15% deflection, the shut off valve is opened and the servo valve is opened at an initial current, followed by a steadily increasing current according to a current ramp rate, leading to an increase in fluid flow to the brake actuators. As illustrated, the aggressive brake fill overshoot302occurs at approximately 15% pedal deflection; the gentle brake fill overshoot304also occurs at approximately 15% pedal deflection. In various embodiments, the rate of opening of the servo valve is controlled by the current ramp rate (e.g., in milliamps/sec) applied to the servo valve. Referring still toFIGS.3A and3B, the value for the current ramp rate inFIG.3A, resulting in an aggressive fill, is greater than the value for the current ramp rate inFIG.3B, leading to a gentle fill. It is noted here that in instances where the brakes are rapidly applied (e.g., slammed on after landing), the effect of the brake fill overshoot illustrated in either ofFIG.3A or3Bwill be minimized (or not felt) as the brake pressure (e.g., the pressure in the brake actuator) very rapidly reaches a high level that exceeds the level of the brake fill overshoot. On the other hand, during braking when taxiing, for example, the brake fill overshoot may be very apparent and undesirable as only minimal brake pressure, on the order of or below the brake fill overshoot, is desired.

Referring now toFIG.4, a graph400of current ramp rate as a function of pressure command (or a curve of current ramp rate versus pressure command) is provided. The graph400represents programming or circuitry typically provided within a BCU, such as, for example, the BCU220described above with reference toFIG.2. In various embodiments, the current ramp rate dictates the current directed to a servo valve, such as, for example, the left servo valve230described above. The current ramp rate is a function of the command pressure, such as, for example, the brake pressure command signal described above. Thus, where a gentle application of the brakes is desired, for example, during taxiing, the BCU commands a current to the servo valve that increases relatively slowly, which results in a gentle brake fill overshoot, similar to that illustrated inFIG.3B. The gentle brake fill overshoot may be felt, but not at the undesirable level that would otherwise occur at a higher current ramp rate. On the other hand, where an aggressive application of the brakes is desired, for example, following landing, the BCU commands a current to the servo valve that increases relatively quickly. Here, as described above, an aggressive brake fill overshoot will result, but will not be apparent because of the otherwise concurrent rapid rise of pressure on the brakes, which exceeds the level of the brake fill overshoot.

As an example, where a pilot desires 500 psi (≈3,447 kPa) be applied at the brake actuators (≈40% pedal deflection inFIGS.3A and3B, or a first brake pedal deflection), which is typical of a brake application during taxi, a current is applied to the servo valve, starting with an initial current of, for example, sixteen milliamps (16 mA), followed by an increase in current at a current ramp rate of six milliamps per second (6 mA/sec) (or a first current ramp rate). Conversely, where a pilot desires 2000 psi (≈13,789 kPa) be applied at the brake actuators (≈93% pedal deflection inFIGS.3A and3B, or a second brake pedal deflection), which is typical of a brake application during landing, a current is applied to the servo valve, starting with an initial current of, for example, sixteen milliamps (16 mA), followed by an increase in current at a current ramp rate of nineteen (19) milliamps per second (or a second current ramp rate). Note that the first current ramp rate and the second current ramp rate will typically correspond to the brake pressure command signal described above with reference toFIG.2(e.g., a first brake pressure command signal and a second brake pressure command signal), and, similarly, are responsive to the pedal deflection signal also described above with reference toFIG.2. In other words, the first current ramp rate may be considered responsive to a first input command pressure signal and the second current ramp rate may be considered responsive to a second input command pressure signal. The relatively slow first current ramp rate (associated with, for example, taxiing) will cause the actuators to be filled with hydraulic fluid or otherwise translated at a slower rate than will occur with the relatively high second current ramp rate (associated with, for example, landing) that will cause the actuators to be filled with hydraulic fluid or otherwise translated at a higher rate.

While a curve402having a smoothly varying and monotonically increasing function is provided, resulting in each value of current ramp rate being a distinct value, it will be appreciated that other curves are contemplated, with various shapes and numerical values (e.g., specific values for current ramp rate as a function of pressure command) being tailored to various applications. For example, a two-level step curve404may be made to approximate a step function, where a constant low current ramp rate and a constant high current ramp rate are selected, depending on the pressure command. Three or four or more step-levels are also contemplated, with each level representing a constant current ramp rate over a range of pressure commands. A straight-line curve406is also contemplated, representing a constant slope function (e.g., y=mx+b) over the applicable range of pressure command. Piecewise linear curves, having, for example, various segments defined by constant current ramp rates or constant slope rates may also be employed. Various other curves are also contemplated, such as, for example, curves defined by trigonometric functions. One such curve, similar to the curve402, is parameterized by a hyperbolic tangent function, for example. Other such curves include the sigmoid function, the error function and the logistic function. One benefit of such curves or other relations between current ramp rate as a function of pressure command is to provide a relatively low current ramp rate at low command pressure (e.g., during taxiing) and a relatively high current rate at high command pressure (e.g., during landing), thereby minimizing undesirable effects of brake fill overshoot.

Referring now toFIG.5, a method500of operating a braking system is described with reference to the following steps. A first step502includes generating a pedal deflection signal (or a brake pedal deflection signal) via a brake pedal or a transducer connected to the brake pedal. A second step504includes providing the pedal deflection signal to a brake control unit. A third step506includes determining by the brake control unit a pressure command signal (or a brake pressure command signal) based on the pedal deflection signal. A fourth step508includes determining by the brake control unit an output current configured to operate a servo valve coupled to a brake actuator, where the output current is increased at a current ramp rate based on the previously determined pressure command signal; as described above, an initial current is generally provided prior to increasing the output current at the current ramp rate. As illustrated inFIG.4, the current ramp rate is a function of the pressure command signal and, accordingly, may represent one of a first current ramp rate or a second current ramp rate (or any number of current ramp rates) that represent distinct values on a curve of current ramp rate versus pressure command. A fifth step510includes terminating the increase in the output current and switching from a brake fill mode to a pressure control mode once a pressure sensor informs the brake control unit that a brake pressure within the actuator has reached a contact pressure threshold.

Although described chiefly in the context of a hydraulic brake system, it will be appreciated that aspects of the disclosure may be applied to electric brakes as well. For example, with an electric brake, a brake fill-like condition can occur when a brake actuator is running clearance prior to engaging a brake stack. This clearance take-up produces provides essentially the same effect as a brake fill condition in a hydraulic brake and can be minimized as described above by sensing the condition and scaling the current ramp rate. Accordingly, as used in this description, the terms power or power source includes a hydraulic power source and power, an electric power source and power, or a pneumatic power source and power. In the context of a hydraulic or a pneumatic system, an effect resulting from power supplied to an actuator includes hydraulic or pneumatic pressure. In the context of an electric system, an effect of power supplied to an actuator includes a magnetic field.