Patent Description:
Lift devices commonly include a vertically movable platform that is supported by a foldable series of linked supports. The linked supports are arranged in an "X" pattern, crisscrossing with one another. A known lift device according to the preamble of claim <NUM> is disclosed in the document <CIT>.

A hydraulic cylinder generally controls vertical movement of the platform by engaging and rotating (i.e., unfolding) the lowermost set of linked supports, which in turn unfolds the remainder of the series of linked supports within the system. The platform raises and lowers based upon the degree of actuation by the hydraulic cylinder. A hydraulic cylinder may also control various other vehicle actions, such as, for example, steering or platform tilt functions. Lift devices using one or more hydraulic cylinders require an on-board reservoir tank to store hydraulic fluid for the lifting process.

One exemplary embodiment relates to a lift device device according to claim <NUM>. The lift device comprises a base, a retractable lift mechanism, a work platform, a linear actuator, and an electromagnetic brake. The base has a plurality of wheels. The retractable lift mechanism has a first end coupled to the base and is moveable between an extended position and a retracted position. The work platform is configured to support a load. The work platform is coupled to and supported by a second end of the retractable lift mechanism. The linear actuator is configured to selectively move the retractable lift mechanism between the extended position and the retracted position. The linear actuator has an electric motor. The electromagnetic brake is coupled to the linear actuator and movable between an engaged position, in which the retractable lift mechanism is prevented from moving between the extended position and the retracted position, and a disengaged position, in which the retractable lift mechanism is allowed to move between the extended position and the retracted position. In the event of a power failure, the electromagnetic brake is biased toward the engaged position.

The invention is capable of other embodiments and of being carried out in various ways. Alternative exemplary embodiments relate to other features and combinations of features as may be recited herein.

Referring to the figures generally, the various exemplary embodiments disclosed herein relate to systems, apparatuses, and methods for the controlled descent of a work platform on a lift device. The lift device includes an electromagnetic brake that is configured to engage in the event of a power failure (e.g., a battery discharge or a control system failure) to hold the work platform in place (i.e., at a constant height). The lift device further includes a manual release mechanism to selectively release the electromagnetic brake to lower the work platform in the event of a battery discharge or a control system failure. The lift device further includes a descent limiting mechanism that limits the speed at which the work platform is allowed to lower when the electromagnetic brake is disengaged. Thus, the lift device allows for the work platform and any worker on the work platform to be safely lowered from a deployed work position in the event of a battery discharge or a control system failure.

According to the exemplary embodiment depicted in <FIG> and <FIG>, a vehicle, shown as vehicle <NUM>, is illustrated. The vehicle <NUM> may be a scissor lift, for example, which can be used to perform a variety of different tasks at various elevations. The vehicle <NUM> includes a base <NUM> supported by wheels 14A, 14B positioned about the base <NUM>. The vehicle <NUM> further includes a battery <NUM> positioned on board the base <NUM> of the vehicle <NUM> to supply electrical power to various operating systems present on the vehicle <NUM>.

The battery <NUM> can be a rechargeable lithium-ion battery, for example, which is capable of supplying a direct current (DC) or alternating current (AC) to controls, motors, actuators, and the like included on board the vehicle <NUM>. The battery <NUM> can include at least one input <NUM> capable of receiving electrical current to recharge the battery <NUM>. In some embodiments, the input <NUM> is a port capable of receiving a plug in electrical communication with an external power source, like a wall outlet. The battery <NUM> can be configured to receive and store electrical current from one of a traditional <NUM> V outlet, a <NUM> V outlet, a <NUM> V outlet, an electrical power generator, or another suitable electrical power source.

The vehicle <NUM> further includes a retractable lift mechanism, shown as a scissor lift mechanism <NUM>, coupled to the base <NUM>. The scissor lift mechanism <NUM> supports a work platform <NUM> (shown in <FIG>). As depicted, a first end <NUM> of the scissor lift mechanism <NUM> is anchored to the base <NUM>, while a second end <NUM> of the scissor lift mechanism <NUM> supports the work platform <NUM>. As illustrated, the scissor lift mechanism <NUM> is formed of a foldable series of linked support members <NUM>. The scissor lift mechanism <NUM> is selectively movable between a retracted or stowed position (shown in <FIG>) and an extended, deployed, or work position (shown in <FIG>) using an actuator, shown as linear actuator <NUM>. The linear actuator <NUM> is an electric actuator. The linear actuator <NUM> controls the orientation of the scissor lift mechanism <NUM> by selectively applying force to the scissor lift mechanism <NUM>. When a sufficient force is applied to the scissor lift mechanism <NUM> by the linear actuator <NUM>, the scissor lift mechanism <NUM> unfolds or otherwise deploys from the stowed or retracted position into the work position. Because the work platform <NUM> is coupled to the scissor lift mechanism <NUM>, the work platform <NUM> is also raised away from the base <NUM> in response to the deployment of the scissor lift mechanism <NUM>.

As shown in <FIG>, the vehicle <NUM> further includes a vehicle controller <NUM> and a lift motor controller <NUM>. The vehicle controller <NUM> is in communication with the lift motor controller <NUM> and is configured to control various driving systems on the vehicle <NUM>. The lift motor controller <NUM> is in communication with the linear actuator <NUM> and is configured to control the movement of the scissor lift mechanism <NUM>. Communication between the lift motor controller <NUM> and the linear actuator <NUM> and/or between the vehicle controller <NUM> and the lift motor controller <NUM> can be provided through a hardwired connection or through a wireless connection (e.g., Bluetooth, Internet, cloud-based communication system, etc.). It should be understood that each of the vehicle controller <NUM> and the lift controller <NUM> includes various processing and memory components configured to perform the various activities and methods described herein. For example, in some instances, each of the vehicle controller <NUM> and the lift controller <NUM> includes a processing circuit having a processor and a memory. The memory is configured to store various instructions configured to, when executed by the processor, cause the vehicle <NUM> to perform the various activities and methods described herein.

As illustrated in the exemplary embodiment provided in <FIG>, the linear actuator <NUM> includes a push tube assembly <NUM>, a gear box <NUM>, and an electric lift motor <NUM>. The push tube assembly <NUM> includes a protective outer tube <NUM> (shown in <FIG> and <FIG>), a push tube <NUM>, and a nut assembly <NUM> (shown in <FIG>). The protective outer tube <NUM> has a trunnion connection portion <NUM> disposed at a proximal end <NUM> thereof. The trunnion connection portion <NUM> is rigidly coupled to the gear box <NUM>, thereby rigidly coupling the protective outer tube <NUM> to the gear box <NUM>. The trunnion connection portion <NUM> further includes a trunnion mount <NUM> that is configured to rotatably couple the protective outer tube <NUM> to one of the support members <NUM> (as shown in <FIG>).

The protective outer tube <NUM> further includes an opening at a distal end <NUM> thereof. The opening of the protective outer tube <NUM> is configured to slidably receive the push tube <NUM>. The push tube <NUM> includes a connection end, shown as trunnion mount <NUM>, configured to rotatably couple the push tube <NUM> to another one of the support members <NUM> (as shown in <FIG>). As will be discussed below, the push tube <NUM> is slidably movable and selectively actuatable between an extended position (shown in <FIG>) and a retracted position (shown in <FIG>).

Referring now to <FIG>, the push tube <NUM> is rigidly coupled to the nut assembly <NUM>, such that motion of the nut assembly <NUM> results in motion of the push tube <NUM>. The push tube <NUM> and the nut assembly <NUM> envelop a central screw rod. The central screw rod is rotatably engaged with the gear box <NUM> and is configured to rotate within the push tube <NUM> and the nut assembly <NUM>, about a central axis of the push tube assembly <NUM>. The nut assembly <NUM> is configured to engage the central screw rod and translate the rotational motion of the central screw rod into translational motion of the push tube <NUM> and the nut assembly <NUM>, with respect to the central screw rod, along the central axis of the push tube assembly <NUM>. In some embodiments, the nut assembly <NUM> may be, for example, a ball screw assembly or a roller screw assembly. In some other embodiments, the nut assembly <NUM> may be any other suitable assembly for translating rotational motion of the central screw rod into translational motion of the push tube <NUM> and the nut assembly <NUM>.

Referring again to <FIG>, the lift motor <NUM> is configured to selectively provide rotational actuation to the gear box <NUM>. The rotational actuation from the lift motor <NUM> is then translated through the gear box <NUM> to selectively rotate the central screw rod of the push tube assembly <NUM>. The rotation of the central screw rod is then translated by the nut assembly <NUM> to selectively translate the push tube <NUM> and the nut assembly <NUM> along the central axis of the push tube assembly <NUM>. Accordingly, the lift motor <NUM> is configured to selectively actuate the push tube <NUM> between the extended position and the retracted position. Thus, with the trunnion mount <NUM> of the protective outer tube <NUM> and the trunnion mount <NUM> of the push tube <NUM> each rotatably coupled to their respective support members <NUM>, the lift motor <NUM> is configured to selectively move the scissor lift mechanism <NUM> to various heights between and including the retracted or stowed position and the deployed or work position.

The lift motor <NUM> may be an AC motor (e.g., synchronous, asynchronous, etc.) or a DC motor (shunt, permanent magnet, series, etc.). In some instances, the lift motor <NUM> is in communication with and powered by the battery <NUM>. In some other instances, the lift motor <NUM> may receive electrical power from another electricity source on board the vehicle <NUM>.

As depicted in the exemplary embodiment shown in <FIG>, the lift motor <NUM> includes an electromagnetic brake <NUM> configured to hold the work platform <NUM> in place (i.e., at a constant height) in the case of a battery discharge or a control system failure. As illustrated in <FIG>, the electromagnetic brake <NUM> includes a pressure plate <NUM>, a friction disk <NUM>, an armature <NUM>, a magnetic body <NUM>, and a wire coil <NUM>. As illustrated, the pressure plate <NUM> is disposed at a first end <NUM> of the electromagnetic brake <NUM>. The pressure plate <NUM> surrounds a hub <NUM>. The hub <NUM> is fixed to a rotor <NUM> of the lift motor <NUM>, such that the hub <NUM> and the rotor <NUM> are rotationally coupled (e.g., rotation of one of the hub <NUM> and the rotor <NUM> results in the rotation of the other of the hub <NUM> and the rotor <NUM>). The friction disk <NUM> is disposed adjacent the pressure plate <NUM>. The friction disk <NUM> is fixed to the hub <NUM>, such that of the hub <NUM>, the rotor <NUM>, and the friction disk <NUM> are all rotationally coupled (e.g., rotation of one of the hub <NUM>, the rotor <NUM>, and the friction disk <NUM> results in the rotation of the other two of the hub <NUM>, the rotor <NUM>, and the friction disk <NUM>). The armature <NUM> is disposed adjacent the friction disk <NUM>, and is biased into contact with the friction disk <NUM> by engagement springs <NUM>.

The magnetic body <NUM> and the wire coil <NUM> are disposed at a second end <NUM> of the electromagnetic brake <NUM>. The magnetic body <NUM> and the wire coil <NUM> are configured to selectively produce a magnetic force on the armature <NUM> to pull the armature <NUM> toward the magnetic body <NUM>.

Referring now to <FIG>, the electromagnetic brake <NUM> is shown in an engaged position. Specifically, when there is no power applied to the wire coil <NUM> of the lift motor <NUM>, the magnetic body <NUM> and the wire coil <NUM> do not produce any magnetic force on the armature <NUM>. As such, the engagement springs <NUM> bias the armature <NUM> against the friction disk <NUM>, thereby preventing rotation of the friction disk <NUM>. Because the friction disk <NUM> is fixed to the hub <NUM>, and the hub is rigidly coupled to the rotor <NUM>, the rotor <NUM> is also prevented from rotating, thereby preventing the work platform <NUM> from moving vertically (e.g., because the central screw rod is prevented from spinning, such that the linear actuator is prevented from translating). Accordingly, when no power is applied to the wire coil <NUM> of the lift motor <NUM>, the electromagnetic brake <NUM> is biased toward the engaged position.

Referring now to <FIG>, the electromagnetic brake <NUM> is shown in a disengaged position. Specifically, when power (e.g., a current) is applied to the wire coil <NUM> of the lift motor <NUM>, the magnetic body <NUM> and the wire coil <NUM> produce an electromagnetic force on the armature <NUM>, compressing the engagement springs <NUM> and pulling the armature <NUM> out of contact with the friction disk <NUM>. Accordingly, the friction disk <NUM>, the hub <NUM>, and the rotor <NUM> are all free to rotate. As such, the lift motor <NUM> is allowed to function normally.

During normal operation, when the lift motor <NUM> is commanded to lift or lower the work platform <NUM>, power is also applied to the wire coil <NUM> to allow for the lift motor <NUM> to function as intended. Then, when the lift motor <NUM> is not being commanded to lift or lower the work platform <NUM>, power is not applied to the wire coil <NUM>, such that the friction disk <NUM> is engaged by the armature <NUM>, and the work platform <NUM> is prevented from moving vertically.

As such, in the event of a power failure (e.g., the battery <NUM> is discharged or the control system fails), when power is cut from the wire coil <NUM>, the electromagnetic brake <NUM> is configured to automatically return to the engaged position, and the scissor lift mechanism <NUM> is prevented from moving between the extended position and the retracted position. In some embodiments, if the battery <NUM> is discharged or the control system fails when the scissor lift mechanism <NUM> is in the extended position (i.e., the work platform <NUM> is in a raised position) it may be desired to allow for the work platform <NUM> (and any users working on the work platform <NUM>) to be safely lowered from the raised or deployed position back down to the stowed or lowered position.

Accordingly, as illustrated in the exemplary embodiment shown in <FIG>, the vehicle <NUM> further includes a manual release device <NUM> and a descent limiting mechanism, shown as centrifugal brake <NUM>. The manual release device <NUM> is configured to manually move the electromagnetic brake <NUM> into the disengaged position, such that the work platform <NUM> can be lowered due to gravity. The centrifugal brake <NUM> is configured to provide resistance to and modulate (e.g., mechanically reduce) the speed at which the work platform <NUM> is lowered.

Specifically, the manual release device <NUM> includes a manual pull handle <NUM> (shown in <FIG> and <FIG>) that is connected to a release tab <NUM> (shown in <FIG>) through a Bowden cable <NUM> (shown in <FIG>). As the manual pull handle <NUM> is pulled, the Bowden cable <NUM> pulls on the release tab <NUM>, which is fixed to the armature <NUM>. Accordingly, the armature <NUM> is moved out of contact with the friction disk <NUM>, thereby manually moving the electromagnetic brake <NUM> into the disengaged position and allowing the work platform <NUM> to lower.

The centrifugal brake <NUM> is configured to modulate (e.g., mechanically reduce) the speed at which the rotor <NUM> is allowed to rotate. Specifically, the centrifugal brake <NUM> prevents the work platform <NUM> from descending too rapidly when the electromagnetic brake <NUM> is disengaged. Specifically, as best shown in <FIG>, the centrifugal brake <NUM> includes a rotor connection portion <NUM>, a pair of weights <NUM>, a pair of retention springs <NUM>, and a casing <NUM>. The rotor connection portion <NUM> is rotationally fixed to the rotor <NUM> (e.g., through a keyway connection, a set screw, or any other suitable connection). The pair of weights <NUM> are disposed on opposite sides of the rotor connection portion <NUM>. The pair of weights <NUM> are configured to engage the rotor connection portion <NUM>, such that rotation of the rotor connection portion <NUM> results in rotation of the pair of weights <NUM>, and vice versa. Each weight <NUM> of the pair of weights <NUM> includes a frictional outer surface <NUM>. The pair of retention springs <NUM> are configured to maintain an inwardly-biased force on the pair of weights <NUM>, generally directed toward the rotor <NUM>.

During operation, as the rotor <NUM> rotates, the pair of weights <NUM> tend to move radially outward, away from the rotor <NUM>. The pair of retention springs <NUM> are configured to provide a radially-inward (i.e., toward the rotor <NUM>) force onto the weights <NUM>, preventing the frictional outer surface <NUM> of the weights <NUM> from contacting a frictional inner surface <NUM> of the casing <NUM>, and thus from reducing the rotational speed of the rotor <NUM>, until the rotor <NUM> exceeds a predetermined rotational speed. That is, in some embodiments, the centrifugal brake <NUM> is configured to reduce the rotational speed of the rotor <NUM> once the rotational speed of the rotor <NUM> reaches or exceeds the predetermined rotational speed.

In some embodiments, the predetermined rotational speed may be approximately <NUM> rpm. In some other embodiments, the predetermined rotational speed may be between <NUM> rpm and <NUM> rpm. In yet some other embodiments, the predetermined rotational speed may be more than <NUM> rpm or less than <NUM> rpm, as desired for a given application. Once the rotor <NUM> exceeds the predetermined rotational speed, the required centripetal force needed to retain the weights adjacent the rotor connection portion <NUM> exceeds the spring force, allowing the weights to move radially outward. As such, the frictional outer surface <NUM> of the weights <NUM> contacts the frictional inner surface <NUM> of the casing <NUM>, which effectively limits the rotational speed of the rotor <NUM>.

As such, during operation, in the event that the battery <NUM> is discharged or the control system fails, the manual release device <NUM> and the centrifugal brake <NUM> allow for the work platform <NUM> to be safely lowered from the deployed position. Further, in the event that the manual pull handle <NUM> is pulled during normal operation, the lift motor controller <NUM> may be configured to control the descent of the work platform <NUM> using the lift motor <NUM>.

Although the illustrated centrifugal brake <NUM> is shown opposite the gear box <NUM> from the lift motor <NUM>, in some embodiments, the centrifugal brake <NUM> may alternatively be located between the gear box <NUM> and the lift motor <NUM>. In some other embodiments, the centrifugal brake <NUM> may be alternatively located opposite the electromagnetic brake <NUM> from the lift motor <NUM>.

Further, in some embodiments, the descent limiting mechanism may be replaced by various other types of brake mechanisms that are configured to limit the rotational speed of the rotor <NUM>. For example, in some embodiments, the linear actuator <NUM> may alternatively or additionally include a shoe brake, a drum brake, a disk brake, or any other suitable brake mechanism, as desired for a given application.

Additionally, in some embodiments, in addition to or in place of the centrifugal brake <NUM>, the linear actuator <NUM> may include a descent limiting mechanism in the form of a permanent magnet motor. The permanent magnet motor has terminals that are biased toward a shunted position, but are actively held open during normal operation. As such, in the event of the battery <NUM> being discharged or the control system failing, the terminals are shunted together, such that the permanent magnet motor acts like a generator. With the permanent magnet motor acting like a generator, the speed at which the rotor <NUM> is allowed to rotate would be effectively reduced.

In some embodiments, the lift motor <NUM> may be a permanent magnet motor, and may be configured to both selectively actuate the linear actuator <NUM>, while also having terminals that are biased toward a shunted position in the case of the battery <NUM> being discharged or the control system failing, such that the lift motor <NUM> acts as a generator and reduces the speed of the rotor <NUM> in the case of a battery discharge or a control system failure.

Referring again to <FIG> and <FIG>, the battery <NUM> can also be in communication with the vehicle controller <NUM>, which can command the battery <NUM> to selectively supply electrical power to a drive motor <NUM> to propel the vehicle <NUM>. The drive motor <NUM> may similarly be an AC motor (e.g., synchronous, asynchronous, etc.) or a DC motor (shunt, permanent magnet, series, etc.) for example, which receives electrical power from the battery <NUM> or other electricity source on board the vehicle <NUM> and converts the electrical power into rotational energy in a drive shaft. The drive shaft can be used to drive the wheels 14A, 14B of the vehicle <NUM> using a transmission. The transmission can receive torque from the drive shaft and subsequently transmit the received torque to a rear axle <NUM> of the vehicle <NUM>. Rotating the rear axle <NUM> also rotates the rear wheels 14A on the vehicle <NUM>, which propels the vehicle <NUM>.

The rear wheels 14A of the vehicle <NUM> can be used to drive the vehicle, while the front wheels 14B can be used to steer the vehicle <NUM>. In some embodiments, the rear wheels 14A are rigidly coupled to the rear axle <NUM>, and are held in a constant orientation relative to the base <NUM> of the vehicle <NUM> (e.g., approximately aligned with an outer perimeter <NUM> of the vehicle <NUM>). In contrast, the front wheels 14B are pivotally coupled to the base <NUM> of the vehicle <NUM>. The wheels 14B can be rotated relative to the base <NUM> to adjust a direction of travel for the vehicle <NUM>. Specifically, the front wheels 14B can be oriented using an electrical steering system <NUM>. In some embodiments, the steering system <NUM> may be completely electrical in nature, and may not include any form of hydraulics.

It should be appreciated that, while the retractable lift mechanism included on vehicle <NUM> is a scissor lift mechanism, in some instances, a vehicle may be provided that alternatively includes a retractable lift mechanism in the form of a boom lift mechanism. For example, in the exemplary embodiment depicted in <FIG>, a vehicle, shown as vehicle <NUM>, is illustrated. The vehicle <NUM> includes a retractable lift mechanism, shown as boom lift mechanism <NUM>. The boom lift mechanism <NUM> is similarly formed of a foldable series of linked support members <NUM>. The boom lift mechanism <NUM> is selectively movable between a retracted or stowed position and a deployed or work position using a plurality of actuators <NUM>. Each of the plurality of actuators <NUM> is a linear actuator similar to the linear actuator <NUM>.

It should be further appreciated that the linear actuators used in the lift mechanism <NUM>, <NUM>, as well as in the steering system <NUM>, may be incorporated into nearly any type of electric vehicle. For example, the electric systems described herein can be incorporated into, for example, a scissor lift, an articulated boom, a telescopic boom, or any other type of aerial work platform.

Advantageously, vehicles <NUM>, <NUM> may be fully-electric lift devices. All of the electric actuators and electric motors of vehicles <NUM>, <NUM> can be configured to perform their respective operations without requiring any hydraulic systems, hydraulic reservoir tanks, hydraulic fluids, engine systems, etc. That is, both vehicles <NUM>, <NUM> may be completely devoid of any hydraulic systems and/or hydraulic fluids generally. Said differently, both vehicles <NUM>, <NUM> may be devoid of any moving fluids. Traditional lift device vehicles do not use a fully-electric system and require regular maintenance to ensure that the various hydraulic systems are operating properly. As such, the vehicles <NUM>, <NUM> may use electric motors and electric actuators, which allows for the absence of combustible fuels (e.g., gasoline, diesel) and/or hydraulic fluids. As such, the vehicles <NUM>, <NUM> may be powered by batteries, such as battery <NUM>, that can be re-charged when necessary.

References herein to the positions of elements (e.g., "top," "bottom," "above," "below," "between," etc.) are merely used to describe the orientation of various elements in the figures.

The hardware and data processing components used to implement the various processes, operations, illustrative logics, logical blocks, modules and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose single- or multi-chip processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, or, any conventional processor, or state machine. A processor also may be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. The memory (e.g., memory, memory unit, storage device) may include one or more devices (e.g., RAM, ROM, Flash memory, hard disk storage) for storing data and/or computer code for completing or facilitating the various processes, layers and modules described in the present disclosure. The memory may be or include volatile memory or non-volatile memory, and may include database components, object code components, script components, or any other type of information structure for supporting the various activities and information structures described in the present disclosure. According to an exemplary embodiment, the memory is coupled to the processor to form a processing circuit and includes computer code for executing (e.g., by the processor) the one or more processes described herein.

Claim 1:
A lift device comprising:
a base (<NUM>) having a plurality of wheels (14A, 14B);
a retractable lift mechanism (<NUM>) having a first end (<NUM>, <NUM>) coupled to the base (<NUM>) and being moveable between an extended position and a retracted position;
a work platform (<NUM>) configured to support a load, the work platform (<NUM>) being coupled to and supported by a second end (<NUM>, <NUM>) of the retractable lift mechanism (<NUM>);
a linear actuator (<NUM>) configured to selectively move the retractable lift mechanism (<NUM>) between the extended position and the retracted position, the linear actuator (<NUM>) having an electric motor;
an electromagnetic brake (<NUM>) coupled to the linear actuator (<NUM>) and movable between an engaged position, in which the retractable lift mechanism (<NUM>) is prevented from moving between the extended position and the retracted position, and a disengaged position, in which the retractable lift mechanism (<NUM>) is allowed to move between the extended position and the retracted position,
wherein the lift device is characterized by
a descent control mechanism configured to reduce a speed at which the retractable lift mechanism (<NUM>) is moved from the extended position to the retracted position; and
the descent control mechanism is a centrifugal brake rotationally coupled to a rotor of the electric motor of the linear actuator (<NUM>).