Patent Description:
The invention is defined in independent claim <NUM> and relates to a method for determining a load supported by a work platform of a lift device. The method comprises providing the lift device including the work platform and a linear actuator configured to support and selectively move the work platform between a raised and a lowered position, the linear actuator having an electric motor and an electromagnetic brake. The method further comprises disengaging the electromagnetic brake of the linear actuator. The method further comprises maintaining a height of the work platform using the electric motor of the linear actuator. The method further comprises determining a motor torque applied by the electric motor. The method further comprises determining an actuator force applied by the linear actuator to the work platform based on the motor torque applied by the electric motor. The method further comprises determining the height of the work platform. The method further comprises determining the load supported by the work platform based on the actuator force applied to the work platform and the height of the work platform.

The invention is also defined in independent claim <NUM> which relates to a lift device. The lift device comprises a base, a retractable lift mechanism, a work platform, a linear actuator, and a lift controller. 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 and an electromagnetic brake. The electromagnetic brake is configured to, when engaged, prevent the linear actuator from moving the retractable lift mechanism between the extended position and the retracted position. The lift controller is in communication with the linear actuator and includes a processing circuit having a processor and a memory. The memory has instructions configured to, when executed by the processor, cause the lift controller to disengage the electromagnetic brake. The instructions are further configured to, when executed by the processor, cause the lift controller to maintain a height of the work platform using the electric motor. The instructions are further configured to, when executed by the processor, cause the lift controller to determine a motor torque applied by the electric motor. The instructions are further configured to, when executed by the processor, cause the lift controller to determine an actuator force applied to the work platform based on the motor torque applied by the electric motor. The instructions are further configured to, when executed by the processor, cause the lift controller to determine the height of the work platform. The instructions are further configured to, when executed by the processor, cause the lift controller to determine the load supported by the work platform based on the actuator force applied to the work platform and the height of the work platform.

A preferred embodiment relates to a fully-electric scissor lift. The fully-electric scissor lift comprises a base, a scissor lift mechanism, a work platform, a linear actuator, and a lift controller. The base has a plurality of wheels. The scissor 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 scissor lift mechanism. The linear actuator is configured to selectively move the scissor lift mechanism between the extended position and the retracted position. The linear actuator has an electric motor, an electromagnetic brake, and a push tube assembly. The electromagnetic brake is configured to, when engaged, prevent the linear actuator from moving the scissor lift mechanism between the extended position and the retracted position. The push tube assembly has a protective outer tube and an inner push tube. The inner push tube includes a strain gauge configured to monitor a compression of the inner push tube. The lift controller is in communication with the linear actuator and includes a processing circuit having a processor and a memory. The memory has instructions configured to, when executed by the processor, cause the lift controller to disengage the electromagnetic brake. The instructions are further configured to, when executed by the processor, cause the lift controller to maintain a height of the work platform using the electric motor. The instructions are further configured to, when executed by the processor, cause the lift controller to determine a motor torque applied by the electric motor. The instructions are further configured to, when executed by the processor, cause the lift controller to determine an actuator force applied to the work platform based on the motor torque applied by the electric motor. The instructions are further configured to, when executed by the processor, cause the lift controller to determine the height of the work platform. The instructions are further configured to, when executed by the processor, cause the lift controller to determine the load supported by the work platform based on the actuator force applied to the work platform, the monitored compression of the inner push tube, and the height of the work platform.

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 sensing a load supported by a work platform. According to the invention, an electromagnetic brake of a lift actuator motor is disengaged and the lift actuator motor is used to maintain a work platform height. A lift controller is then configured to determine the load supported by the work platform using various actuator/motor characteristics and a measured height of the work platform.

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 vehicle <NUM> controls, motors, actuators, and the like. 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 a 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 controller <NUM>. The vehicle controller <NUM> is in communication with the lift controller <NUM>. The lift controller <NUM> is in communication with the linear actuator <NUM> to control the movement of the scissor lift mechanism <NUM>. Communication between the lift controller <NUM> and the linear actuator <NUM> and/or between the vehicle controller <NUM> and the lift 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.

In some embodiments, the vehicle controller <NUM> may be configured to limit the drive speed of the vehicle <NUM> depending on a height of the work platform <NUM>. That is, the lift controller <NUM> may be in communication with a scissor angle sensor <NUM> configured to monitor a lift angle of the bottom-most support member <NUM> with respect to the base <NUM>. Based on the lift angle, the lift controller <NUM> may determine the current height of the work platform <NUM>. Using this height, the vehicle controller <NUM> may be configured to limit or proportionally reduce the drive speed of the vehicle <NUM> as the work platform <NUM> is raised.

As illustrated 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>), an inner 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 inner push tube <NUM>. The inner push tube <NUM> includes a connection end, shown as trunnion mount <NUM>, configured to rotatably couple the inner push tube <NUM> to another one of the support members <NUM> (as shown in <FIG>). As will be discussed below, the inner 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 inner push tube <NUM> is rigidly coupled to the nut assembly <NUM>, such that motion of the nut assembly <NUM> results in motion of the inner push tube <NUM>. The inner 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 inner 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 inner 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>.

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 inner 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 inner 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 inner 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.

In some embodiments, the nut assembly <NUM> may be a ball screw nut assembly. In some other embodiments, the nut assembly <NUM> may be a roller screw nut assembly. In some yet some other embodiments, the nut assembly <NUM> may be any other suitable nut assembly configured to translate the rotational motion of the central screw rod into axial movement of the inner push tube <NUM> and the nut assembly <NUM>.

When the lift motor <NUM> is powered down or discharged, the nut assembly <NUM> allows the scissor lift mechanism <NUM> to gradually retract due to gravity. As such, the lift motor <NUM> includes an electromagnetic brake <NUM> configured to maintain the position of the work platform <NUM> when the lift motor <NUM> is powered down or discharged. In some instances, the electromagnetic brake <NUM> is further configured to aid the lift motor <NUM> in maintaining the position of the work platform <NUM> during normal operation.

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>.

In some embodiments, the linear actuator <NUM> includes various built-in sensors configured to monitor various actuator/motor characteristics. For example, the linear actuator <NUM> may include a motor speed sensor, a motor torque sensor (e.g., a motor current sensor), various temperature sensors, various vibration sensors, etc. The lift controller <NUM> may then be in communication with each of these sensors, and may use real-time information received/measured by the sensors to determine a load held by the work platform <NUM>.

According to the invention, to determine the load held by the work platform <NUM>, the lift controller <NUM> does temporarily disengage the electromagnetic brake <NUM> and maintain the height of the work platform <NUM> using the lift motor <NUM>. As alluded to above, in some instances, the electromagnetic brake <NUM> is configured to aid the lift motor in maintaining the position of the work platform <NUM> during normal operation. By disengaging the electromagnetic brake <NUM>, the full load on the work platform <NUM> must be supported using the lift motor <NUM>. With the full load on the work platform <NUM> being supported by the lift motor <NUM>, the lift controller <NUM> then determines, based on the various actuator/motor characteristics, the load on the work platform <NUM>. In some instances, the electromagnetic brake <NUM> may be disengaged for less than five seconds. In some instances, the electromagnetic brake <NUM> may be disengaged for less than one second.

Referring now to <FIG>, a flow chart is provided, showing the inventive method of determining the load on the work platform <NUM>. As depicted, the lift controller <NUM> first disengages the electromagnetic brake <NUM>, at step <NUM>. The lift controller <NUM> then maintains the height of the work platform <NUM> using the lift motor <NUM>, at step <NUM>.

With the electromagnetic brake <NUM> disengaged and the lift motor <NUM> maintaining the height of the work platform <NUM>, the lift controller <NUM> determines the applied motor torque output by the lift motor <NUM>, at step <NUM>, using a combination of the measured motor current of the lift motor <NUM>, the measured motor slip of the lift motor <NUM>, and various other motor characteristics associated with the lift motor <NUM> (e.g., motor type, winding density of a coil of the lift motor <NUM>, winding material of the coil of the lift motor <NUM>, etc.). The lift controller <NUM> then uses the applied motor torque and a model of the mechanics of the linear actuator <NUM> to determine an actuator force applied by the linear actuator <NUM> on the scissor lift mechanism <NUM>, at step <NUM>.

Before, during, or after determining the actuator force applied by the linear actuator <NUM>, the lift controller <NUM> determines a height of the work platform <NUM>, at step <NUM>, using the lift angle sensed by the scissor angle sensor <NUM> and a model of the mechanics of the scissor lift mechanism <NUM>. The lift controller <NUM> then determines the load supported by the work platform <NUM>, at step <NUM>, using the applied actuator force, the platform height, and a height-force curve for the scissor lift mechanism <NUM>.

In some exemplary embodiments, a strain gauge <NUM> (shown in <FIG>) may be coupled to the inner push tube <NUM> to monitor a compression of the inner push tube <NUM> during operation (e.g., along the axial length of the inner push tube). The lift controller <NUM> may be in communication with the strain gauge <NUM>. Accordingly, the lift controller <NUM> additionally uses the monitored compression of the inner push tube <NUM>, various dimensional characteristics of the inner push tube <NUM> (e.g., length, diameter, thickness, etc.), and the material properties of the inner push tube <NUM> (e.g., Young's modulus) to determine the load supported by the inner push tube <NUM>, and thereby the load supported by the work platform <NUM>.

In some embodiments, the lift controller <NUM> may be configured to limit or scale the lifting functions of the scissor lift mechanism <NUM> based on the determined load supported by the work platform <NUM>. For example, in some instances, the lift controller <NUM> may limit or scale the lifting functions when the load supported by the work platform is between <NUM>% and <NUM>% of a rated capacity of the vehicle <NUM>. For example, between <NUM>% and <NUM>% of the rated capacity, the lift speed (raising or lowering) of the linear actuator <NUM> may be reduced (e.g., <NUM>%, <NUM>%, <NUM>% of normal operation speed).

Referring again to <FIG> and <FIG>, the battery <NUM> can also 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 another 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 <NUM>, <NUM> used in the lift mechanisms <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.

Although this description may discuss a specific order of method steps, the order of the steps may differ from what is outlined. Also two or more steps may be performed concurrently or with partial concurrence. Such variation will depend on the software and hardware systems chosen and on designer choice. All such variations are within the scope of the appended claims.

Likewise, software implementations could be accomplished with standard programming techniques with rule-based logic and other logic to accomplish the various connection steps, processing steps, comparison steps, and decision steps.

As utilized herein, the terms "approximately", "about", "substantially", and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numerical ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the invention as recited in the appended claims.

The terms "coupled," "connected," and the like, as used herein, mean the joining of two members directly or indirectly to one another. Such joining may be stationary (e.g., permanent, etc.) or moveable (e.g., removable, releasable, etc.). Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another.

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. It should be noted that the orientation of various elements may differ according to other exemplary embodiments, and that such variations are intended to be encompassed by the scope of the appended claims.

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 method for determining a load supported by a work platform (<NUM>) of a lift device, the method comprising:
providing the lift device including the work platform (<NUM>) and a linear actuator (<NUM>, <NUM>) configured to support and selectively move the work platform (<NUM>) between a raised and a lowered position, the linear actuator (<NUM>, <NUM>) having an electric motor and an electromagnetic brake (<NUM>);
disengaging the electromagnetic brake (<NUM>) of the linear actuator (<NUM>, <NUM>);
maintaining a height of the work platform (<NUM>) using the electric motor of the linear actuator (<NUM>, <NUM>);
determining a motor torque applied by the electric motor;
determining an actuator force applied by the linear actuator (<NUM>, <NUM>) to the work platform (<NUM>) based on the motor torque applied by the electric motor;
determining the height of the work platform (<NUM>); and
determining the load supported by the work platform (<NUM>) based on the actuator force applied to the work platform (<NUM>) and the height of the work platform (<NUM>),
wherein the motor torque is determined based on at least one of a measured motor current of the electric motor, a measured motor slip of the electric motor, a motor type of the electric motor, a winding density of a coil of the electric motor, and a winding material of the coil of the electric motor,
wherein the lift device is a scissor lift having a foldable series of linked support members (<NUM>, <NUM>) and the height of the work platform (<NUM>) is determined based on a lift angle of at least one linked support member (<NUM>, <NUM>),
wherein the load supported by the work platform (<NUM>) is determined at least partially based on a height-force curve for the lift device, and
wherein the linear actuator (<NUM>, <NUM>) includes a push tube assembly having a protective outer tube and an inner push tube and the load supported by the work platform (<NUM>) is further determined based on a monitored compression of the inner push tube.