Patent Description:
Over time, operation of the rotary servo motor results in wear on one or more of the brake assembly components. Routine maintenance and servicing can generally counteract the effects of wear and tear. However, identifying the root cause of maintenance issues (e.g., performing manual diagnostics) may be difficult and time-consuming, and precautionary replacement or repair of components on a set schedule can be inefficient. <CIT> relates to a brake apparatus with functional integrity monitor. Means for reacting the brake torque directly against calibrated springs are incorporated, as the brake is applied while the drive system is operating, to generate a calibrated relative rotation between components of the braking device. The amount of relative rotation between the components caused by the braking torque acting against the reacting torque of the spring means this provides a direct measurement of braking torque. <CIT> relates to a method and apparatus for controlling motion in a counterbalancing system. A limited amount of movement allows for determining the direction that the sheave is being pulled by activating an electric motor, with the brake engaged, to apply torques in opposing directions. There will be no movement in the direction that the sheave is being pulled, but there will be a limited amount of movement measurable in a direction opposite the direction that the sheave is being pulled due to backlash. The limited amount of movement may be detected by an encoder, and the motor may then pre-apply a correct torque in the direction opposite the direction that the sheave is being pulled before releasing the brake to allow for a smoother transition. <CIT> relates to a paddle retracting method of variable-pitch system. The method is applied when a wind power variable-pitch servo driver fails. A paddle retracting program applying the paddle retracting method is always kept in an activated state, so that the state of the wind power variable-pitch servo driver can be automatically detected when an encoder fails, a paddle retracting action is automatically finished, and paddles are rotated back to a paddle retracting extreme position. <CIT> relates to brake condition monitoring. The actual condition of the brake can be determined by comparing the clearance with one or more limit values. The limit values may determine one or more brake condition levels, in which case the condition of the brake can be determined by comparing the clearance with the limit values. The axle of the device is driven in a first rotation direction when the brake has been turned on. A position angle of the device is measured. The axle of the device is driven in a second rotation direction when the brake has been turned on. The position angle of the axle of the device is measured in the second rotation direction.

It is the object of the present invention to improve accuracy for monitoring brake health.

Aspects of the present disclosure are directed to monitoring brake backlash using a position feedback device of an electric motor. By periodically performing a self-diagnostic routine using onboard components in accordance with the present disclosure, brake wear can be monitored such that replacement of certain components can be performed prior to brake failure.

In accordance with one aspect, a method for measuring motor brake health of a motor assembly having a brake assembly for braking an output shaft of the motor and a position feedback device for measuring an angular position of the output shaft is set forth. The method comprises engaging the brake assembly to restrict rotation of a brake rotor of the brake assembly, energizing the motor assembly to apply a backlash measuring torque level to the output shaft of the motor assembly in a first direction while the brake assembly is engaged, measuring a first angular position of the output shaft with the position feedback device while the backlash measuring torque level is being applied, energizing the motor assembly to apply a backlash measuring torque level to the output shaft in a second direction while the brake assembly is engaged, and measuring a second angular position of the output shaft with the position feedback device while the backlash measuring torque level is being applied. The difference between the first angular position and the second angular position corresponds to an amount of backlash between the brake rotor and a brake hub of the brake assembly.

Engaging the brake can be performed by an onboard motor controller of the motor assembly. Energizing the motor assembly to apply a backlash measuring torque level to the output shaft in the first or second direction can also be performed by the onboard motor controller while the brake is engaged. The method includes centering the brake rotor prior to energizing the motor assembly. Centering the brake rotor includes energizing the motor assembly to apply a centering torque level to the output shaft in a first rotational direction and energizing the motor assembly to apply a centering torque level to the output shaft in a second rotation direction. The centering torque level can be greater than the backlash measuring torque level.

In accordance with another aspect, a motor assembly comprises an electric motor, a position feedback device and a brake assembly. The electric motor includes a stator, a rotor and an output shaft configured to be driven by the rotor. The brake assembly is operatively coupled to the output shaft for braking rotation of the output shaft, the brake assembly includes a brake hub fixed to the output shaft for rotation therewith and a brake rotor rotationally coupled to the brake hub. The position feedback device is configured to measure an angular position of the output shaft. A motor controller is operatively coupled to the electric motor and the brake assembly and includes a brake diagnostic module configured to engage the brake assembly to restrict rotation of the brake rotor, energize the electric motor to apply a backlash measuring torque level to the output shaft of the motor assembly in a first direction while the brake assembly is engaged, measure a first angular position of the output shaft with the position feedback device while the backlash measuring torque level is being applied, energize the motor assembly to apply a backlash measuring torque level to the output shaft in a second direction while the brake assembly is engaged, and measure a second angular position of the output shaft with the position feedback device while the backlash measuring torque level is being applied. The difference between the first angular position and the second angular position corresponds to an amount of backlash between the brake rotor and a brake hub of the brake assembly.

The electric motor can be a servo motor. The brake assembly can include a coil and at least one spring for biasing an armature of the coil toward a brake engaged position, the coil being configured to disengage the brake when energized by the onboard controller. The brake rotor and brake hub can have mating splines, the brake rotor being movable axially relative to the brake rotor during brake engagement and disengagement. The splines can be trapezoidal in cross-section. The onboard controller is configured to center the brake rotor prior to energizing the motor. Centering the brake rotor includes energizing the motor to apply a centering torque level to the output shaft in a first rotational direction and energizing the motor to apply a centering torque level to the output shaft in a second rotation direction. The centering torque level can be greater than the backlash measuring torque level.

In accordance with another aspect, a motor controller is set forth for a motor assembly having an electric motor with an output shaft, a brake assembly for braking rotation of the output shaft, and a position feedback device. The motor controller comprises a brake diagnostic module configured to engage the brake assembly to restrict rotation of a brake rotor of the brake assembly, energize the electric motor to apply a backlash measuring torque level to the output shaft in a first direction while the brake assembly is engaged, measure a first angular position of the output shaft with the position feedback device while the backlash measuring torque level is being applied, energize the electric motor to apply a backlash measuring torque level to the output shaft in a second direction while the brake assembly is engaged, and measure a second angular position of the output shaft with the position feedback device while the backlash measuring torque level is being applied. The difference between the first angular position and the second angular position corresponds to an amount of backlash between the brake rotor and a brake hub of the brake assembly.

The onboard controller is further configured to center the brake rotor prior to energizing the electric motor. Centering the brake rotor includes energizing the motor to apply a centering torque level to the output shaft in a first rotational direction and energizing the motor to apply a centering torque level to the output shaft in a second rotation direction. The centering torque level can be greater than the backlash measuring torque level.

With reference to <FIG>, an exemplary motor assembly is illustrated and identified generally by reference numeral <NUM>. It will be appreciated that aspects of the present disclosure are applicable to a wide variety of electric motor configurations, as well as other applications where a rotating shaft is present (e.g., pumps, etc.). Accordingly, it should be understood that many of the features of the motor are exemplary in nature and intended to give context to certain aspects of the disclosure.

The exemplary motor assembly <NUM> generally includes a housing <NUM> for supporting and/or enclosing the various internal components of the motor <NUM>, as will be described below. The housing <NUM> includes a main tubular portion <NUM>, a front bearing support/front plate <NUM> and rear bearing support <NUM>, and an end cap <NUM>. Together, these housing components form a sealed internal chamber (or multiple chambers) for housing, among other things, the rotating elements of the motor, related circuitry and a position feedback device. An electrical connector <NUM> provides a connection point for coupling the motor <NUM> to a motor drive (not shown).

An output shaft <NUM> extends from the housing <NUM> for connection to an associated component to be driven by the motor assembly <NUM>. The output shaft <NUM> in the illustrated embodiment includes a keyway <NUM> for receiving a key <NUM> for rotationally coupling the output shaft <NUM> to the associated component. Other coupling arrangements and/or devices are possible.

The output shaft <NUM> is supported for rotation by front and rear bearings <NUM> and <NUM> which are supported, respectively, by the front bearing support/front plate <NUM> and the rear bearing support <NUM>. As is typical, a rotor <NUM> is fixed to the output shaft <NUM> for rotation therewith, while a stator <NUM> is fixed relative to the tubular main portion <NUM> of the housing <NUM>. A position feedback device, which in the illustrated embodiment is an encoder <NUM>, is mounted to the rear bearing support <NUM>. The encoder <NUM> is engaged with the output shaft <NUM> and provides feedback indicative of, among other things, the angular position of the output shaft <NUM>. The illustrated exemplary motor <NUM> further includes a brake assembly <NUM> for braking rotation of the output shaft <NUM>.

With additional reference to <FIG>, the brake assembly <NUM> is shown in partial cutaway view isolated from the motor assembly <NUM>. The brake assembly <NUM> generally includes a brake housing <NUM> in which a coil <NUM> and a plurality of springs <NUM> are supported. An armature <NUM> associated with the coil <NUM> is configured to compress the springs <NUM> when energized. When the coil <NUM> is not energized, the springs <NUM> force the armature <NUM> against a brake rotor <NUM>. The brake rotor <NUM> is splined to a brake hub <NUM>, which in turn is fixed for rotation with the output shaft <NUM> of the motor assembly <NUM>. Pressure from the springs <NUM> causes the armature <NUM> to clamp the brake rotor <NUM> against an end plate <NUM> thus braking the output shaft <NUM>. Friction material <NUM> on the brake rotor <NUM> enhances the brake's holding ability. The brake assembly <NUM> is often referred to as a spring-set, fail-safe brake.

It should be appreciated that the brake rotor <NUM> is designed to float on the brake hub <NUM> to allow for relatively axial movement therebetween during application and release of braking force. As such, a small tolerance in dimensions is maintained between the splines of the brake rotor <NUM> and the splines of the brake hub <NUM> to prevent binding. If the tolerance is too tight, the brake rotor <NUM> will bind on the brake hub <NUM> and fail to fully release from the end plate resulting in brake drag and/or premature brake failure.

A new or unworn brake assembly typically has a minimal amount of backlash between the brake rotor <NUM> and brake hub <NUM>. Backlash is a well-known concept in the field of mechanical engineering, but for the purposes of this disclosure backlash can broadly be understood to correspond to the amount of rotational play between the brake rotor <NUM> and the brake hub <NUM>. As noted, some backlash may be present in a new or unworn brake, but excessive backlash can be problematic. Backlash tends to increase over time through wearing of the surfaces of the splines on one or both of the brake rotor <NUM> and brake hub <NUM>.

<FIG> illustrates a brake rotor/brake hub assembly with excessive backlash as indicated by arrow A. It should be appreciated that in the illustrated example, the softer metal (aluminum) of the brake hub <NUM> has worn considerably against the harder metal (steel) of the brake hub <NUM> resulting in the excessive backlash.

It has been found that many brake assemblies wear relatively uniformly (e.g., in a predictable relatively linear fashion) until a threshold level of backlash is reached. After the threshold level of backlash is reached, brake wear accelerates in a more exponential fashion.

For example, <FIG> illustrates a graph 80of cycles vs. backlash (in arc minutes). As can be seen, until about <NUM> cycles, backlash increases relatively steadily. After about <NUM> cycles, backlash increases at a much higher rate. The increased rate is due at least in part to a change in spline geometry. That is, at a certain point the geometry of the splines is worn substantially enough that further cycling causes rapid additional wear.

Accordingly, aspects of the present disclosure are directed to monitoring the backlash such that corrective action can be taken prior to or within a period of time after reaching the inflection point of brake wear (e.g., <NUM> cycles in the case of the brake assembly of <FIG>).

With reference to <FIG>, a flowchart is shown illustrating a method <NUM> for measuring motor brake health. The method includes applying the brake assembly to hold the brake rotor in place (e.g., deenergizing the coil to restrict rotation of the brake rotor), centering the brake rotor (e.g., applying high torque to the drive shaft in both clockwise and counterclockwise directions), and applying a low torque to the drive shaft in the clockwise and counterclockwise and obtaining rotational position data from the encoder to determine the amount of play between the brake rotor and the brake hub. The method <NUM> will be described in connection with the motor assembly <NUM> shown in <FIG> and <FIG>, but it should be appreciated that the method can be implemented on a wide variety of motor assemblies when such motor assemblies are properly configured to allow torqueing of the motor with the brake engaged.

The method <NUM> begins in process step <NUM> wherein the brake assembly <NUM> of the motor assembly <NUM> is engaged. As noted above, this is typically performed by de-energizing the coil <NUM> of the brake assembly <NUM>. In some motor circuitry or drive logic, the brake assembly is configured to be energized (brake disengaged) anytime the motor assembly is generating torque at the output shaft. However, the motor assembly <NUM> in accordance with the present disclosure is capable of de-energizing the brake assembly <NUM> (brake engaged) at the same time the motor assembly is generating torque at the output shaft, for example, when operated in a brake diagnostic mode.

Once the brake assembly is engaged, in process steps <NUM> and <NUM>, the motor assembly generates a relatively high torque (e.g., a centering torque) on the output shaft <NUM> in both the clockwise and counterclockwise rotational directions to center the brake rotor <NUM> and/or otherwise ensure the brake rotor <NUM> is freely floating on the brake hub <NUM>. This step essentially shakes or jars the brake assembly to ensure that the rotor is free from interference due to, for example, brake dust particles or other foreign materials. If the brake rotor <NUM> is not centered and/or freely floating on the brake hub <NUM>, the remaining steps may not produce a reliable measurement of brake backlash.

In process step <NUM>, a relatively low torque which is a backlash measuring torque is applied by the motor in a clockwise direction. As will be appreciated, the output shaft <NUM> and brake hub <NUM> may rotate relative to the brake rotor <NUM> until such time as any clearance between a first side of the splines of the brake hub <NUM> and a first side of the splines of the brake rotor <NUM> engage. As the brake is engaged, further rotation of the output shaft <NUM> and brake hub <NUM> is prevented. An angular position of the output shaft is then recorded using the encoder <NUM> in process step <NUM>.

In process step <NUM>, a relatively low torque is applied by the motor in a counter-clockwise direction. As will be appreciated, the output shaft <NUM> and brake <NUM> may rotate relative to the brake rotor <NUM> until such time as any clearance between a second side of the splines of the brake hub <NUM> and a second side of the splines of the brake rotor <NUM> engage. As the brake is engaged, further rotation of the output shaft <NUM> and brake hub <NUM> is prevented. An angular position of the output shaft <NUM> is then recorded in process step <NUM>. The difference between the angular positions recorded in process steps <NUM> and <NUM> is the brake backlash.

In one example, the low torque (e.g., backlash measuring torque) applied by the motor is less than <NUM>% of the continuous rated motor torque value, while the high torque (e.g., centering torque) applied by the motor is more than <NUM>% of the continuous rated motor torque value, and possibly between <NUM>-<NUM>% of the continuous rated motor torque value.

<FIG> is a block diagram showing a servo motor brake health monitoring and diagnostic system S according to an embodiment of the present disclosure. The motor M is operably connected to an electronic motion control system MCS such as an industrial automation control system or other electronic control system or processor. The motion control system MCS is operably connected to a motor drive MD which comprises electronic circuitry for controlling the motor M and brake assembly BA thereof in response to control inputs received from the motion control system MCS. The motor M includes an onboard motor controller MC that is part of the motor M, itself, and that is operably connected to the motor drive MD via connector C. The motor controller MC comprises one or more processing units, ASICS, and/or other electronic circuits for controlling the motor M in response to input commands received from the motor drive MD including input commands that specify a desired angular position for the output shaft OS and a speed at which the output shaft OS is to rotate. Typically, the motor controller MC selectively energizes the motor windings <NUM> of a stator to drive a rotor (not shown) in clockwise or counterclockwise directions using pulse width modulation (PWM) voltage signals <NUM> output by a PWM voltage control module <NUM> of the onboard motor controller MC. The onboard motor controller MC receives feedback or error signals <NUM> from the encoder E indicating the actual angular position of the rotor and output shaft OS, and the onboard motor controller MC continuously alters the PWN voltage signals <NUM> in response to the feedback received from the encoder E to reduce the error to zero at which time the output shaft OS is located in the specified angular position input by the motor drive MD.

The onboard motor controller MC further comprises a brake controller BC as a part thereof. The brake controller BC comprises one or more electronic circuits for receiving input from the motor drive MD and motor controller MC as to the desired state of the brake assembly BA (i.e., brake engaged / "on" or brake disengaged / "off"), and the brake controller BC either energizes or de-energizes the brake electromagnetic coil <NUM> to control the brake assembly BA accordingly as generally described, using a coil control voltage signal <NUM> such as a pulse width modulation (PWM) voltage signal.

The brake controller BC includes a brake diagnostics module BD that is configured to, among other things, measure the brake backlash in accordance with the method described in connection with <FIG>. As will be appreciated, the brake diagnostics module BD is capable of simultaneously <NUM>) de-energizing the brake coil <NUM> to engage the brake assembly BA and <NUM>) energizing the motor winding <NUM> to apply torque to the output shaft of the motor at various levels and in both the clockwise and counterclockwise rotational directions.

As noted, aspects of the present disclosure are apply to a wide range of motor assemblies and, therefore, the configuration shown in <FIG> illustrates but one of many possible motor assemblies that can utilize aspects of the present disclosure.

<FIG> illustrates another exemplary servo motor brake health monitoring and diagnostic system S' similar in many respects to system S of <FIG> with like components denoted with a single prime (e.g., MCS', M', MD', BC', BD', E', BA', <NUM>', <NUM>', <NUM>'). The system S' is virtually identical to the system S except that the motor M' does not include the onboard motor controller MC. Instead, the motor drive MD' performs all motor control operations and includes the PWM voltage controller <NUM>' and the brake controller BC' with brake diagnostics BD', while the encoder E' provides feedback to the motor drive MD' for carrying out, among other things, the brake diagnostics routines set forth above.

It should now be appreciated that the present disclosure sets forth a method and apparatus for measuring brake backlash using the motor assembly's own position feedback device <NUM>. This enables frequent tracking of brake wear such that the brake can be serviced prior to failure. The information obtained from frequent tracking of brake wear can be used to anticipate brake failure, or to generate an alert that service is required.

Claim 1:
A method for measuring motor brake health of a motor assembly (<NUM>) having a brake assembly (<NUM>) for braking an output shaft (<NUM>) of the motor and a position feedback device (<NUM>) for measuring an angular position of the output shaft, the method comprising:
engaging (<NUM>) the brake assembly to restrict rotation of a brake rotor (<NUM>) of the brake assembly, wherein the brake rotor (<NUM>) is splined to a brake hub (<NUM>), which is fixed for rotation with the output shaft (<NUM>) of the motor assembly (<NUM>);
centering (<NUM>, <NUM>) the brake rotor, wherein centering the brake rotor includes energizing the motor assembly to apply a centering torque level to the output shaft in a first rotational direction and energizing the motor assembly to apply a centering torque level to the output shaft in a second rotation direction;
energizing (<NUM>) the motor assembly to apply a backlash measuring torque level to the output shaft of the motor assembly in a first direction while the brake assembly is engaged, wherein the output shaft and the brake hub rotate relative to the brake rotor until a clearance between a first side of the splines of the brake hub and a first side of the splines of the brake rotor engage, and wherein as the brake assembly is engaged, further rotation of the output shaft (<NUM>) and a brake hub (<NUM>) is prevented;
measuring (<NUM>) a first angular position of the output shaft with the position feedback device while the backlash measuring torque level is being applied;
energizing (<NUM>) the motor assembly to apply a backlash measuring torque level to the output shaft in a second direction while the brake assembly is engaged; and
measuring (<NUM>) a second angular position of the output shaft with the position feedback device while the backlash measuring torque level is being applied;
wherein the difference between the first angular position and the second angular position corresponds to an amount of backlash between the brake rotor and a brake hub of the brake assembly.