Patent Application
20200385255
This disclosure relates to mobile lift devices such as forklifts and aerial work platforms. In particular, the instant disclosure relates to a control system for mobile lift devices in which braking of a driven wheel of the device is controlled in response to the weight of a load on the device that is determined in response to a signal from an electromechanical linear actuator controlling elevation of a lift of the device.
Conventional mobile lift devices include systems that control movement of the mobile lift device along a floor or ground as well as systems that control elevation of a lift of the device. Many conventional devices employ combustion engines to generate movement of the mobile lift device along a floor or ground and hydraulic or pneumatic actuators to control elevation of a lift on the device. In recent years, however, there has been a movement towards electrification of these systems. In particular, newer mobile lift devices frequently employ one or more electric motors to move the device along a floor or ground. Braking of the device is controlled through regenerative braking using the electric motors and through application of one or more brakes. Newer mobile lift devices also frequently employ an electromechanical linear actuator to control elevation of the lift. The use of electromechanical linear actuators has several advantages relative to hydraulic or pneumatic actuators. Electromechanical linear actuators are not subject to failure resulting from fluid leakage. Electromechanical actuators also do not require the use of fluid conduits between elements of the control system for the lift and the labor to connect the conduits. Electromechanical actuators are not subject to variation in operation as a result of changes in temperature which may change the viscosity of fluids. Finally, electromechanical actuators can raise and lower the lift at more consistent speeds whereas hydraulic and pneumatic actuators often produce variable speeds resulting from changes in fluid pressure.
In mobile lift devices that employ electric motor(s) and brake(s) to control movement of the device along the floor or ground, the brakes are typically configured to meet several requirements including maintaining the position of the lift device on an incline in the event of a loss of power and halting movement of the lift device on the floor or ground over a predetermined stopping distance in the event of a loss of power. The brakes are configured, however, to meet worst case scenarios in which the lift on the mobile lift device carries a load having a predetermined maximum allowed weight. As a result, when the lift on the device is not carrying a load or carrying a load having a relatively low weight, the brakes can generate far more torque than is necessary leading to rapid deceleration of the mobile lift device and a risk that the device will tilt, skid or otherwise lose control.
The inventor herein has recognized a need for a mobile lift device and a control system for a mobile lift device that will minimize and/or eliminate one or more of the above-identified deficiencies.
A mobile lift device and a control system for a mobile lift device are provided. In particular, a control system controls braking of a driven wheel in the device in response to the weight of a load on the device that is determined in response to a signal from an electromechanical linear actuator controlling elevation of a lift of the device.
A mobile lift device in accordance with one embodiment includes a body supported on a driven wheel and a lift supported by the body and configured for vertical movement relative to the body. The lift is configured to support a load. The device further includes an electric drive motor configured to cause rotation of the driven wheel and a drive motor brake coupled to the electric drive motor. The device further includes an electromechanical linear actuator configured to raise and lower the lift. The electromechanical linear actuator includes an electric actuator motor. The device further includes a controller configured to determine a weight of the load responsive to a signal generated by the electromechanical linear actuator. The controller is further configured to control at least one of the electric drive motor and the drive motor brake responsive to the weight of the load.
A control system for a mobile lift device in accordance with one embodiment includes an electromechanical linear actuator configured to raise and lower a lift of the mobile lift device. The lift is configured to support a load. The electromechanical linear actuator includes an electric actuator motor. The system further includes a controller configured to determine a weight of the load responsive to a signal generated by the electromechanical linear actuator. The controller is further configured to control at least one of an electric drive motor configured to cause rotation of a driven wheel of the mobile lift device and a drive motor brake coupled to the electric drive motor responsive to the weight of the load.
A mobile lift device and control system for a mobile lift device in accordance with the present teachings is advantageous relative to conventional mobile lift devices and control systems. In particular, the inventive lift device and control system use a signal generated by the electromechanical linear actuator as an indicator of the weight of the load in order to provide improved control of braking for the driven wheel of the mobile lift device. As a result, the braking torque can be varied based on the load and improved control of the mobile lift device during braking is obtained.
The foregoing and other aspects, features, details, utilities, and advantages of the present teachings will be apparent from reading the following description and claims, and from reviewing the accompanying drawings.
Referring now to the drawings wherein like reference numerals are used to identify identical components in the various views,
Body 12 is provided to support, position and orient the other components of device 10. Body 12 may include a frame for mounting exterior components such as wheels 14, lift 16, speed sensor 24 and interface 28 and may define an enclosed space configured to house interior components such as power source 18, drive motors 20, motor brakes 22, linear actuators 26, and controller 30. Body 12 may be made from conventional metals and/or plastics and may include multiple members coupled together through conventional fasteners such as screws, bolts, welds and/or adhesives. In the illustrated embodiment, body 12 includes a mast 32 or frame supporting lift 16. Body 12 also includes a handle 34 through which an operator may steer device 10.
Wheels 14 are provided to support body 12 and allow movement of device 10 along a floor or ground. At least one wheel 14 comprises a driven wheel that rotates in response to torque generated by drive motor 20 and that may be braked by the operation of drive motor 20 (through regenerative braking) and/or drive motor brake 22. One or more wheels 14 may also comprise caster wheels that are not driven by drive motor 20 but which allow rolling and rotational movement of body 12. In certain embodiments, device 10 may include wheel brakes (not shown) for braking any caster wheels on device 10 that operate under the control of controller 30. Depending on the type of mobile lift device 10, device 10 may further include outriggers or other mechanisms for balancing device 10.
Lift 16 provides a means for supporting a load. The load may comprise an empty or loaded pallet or an object. In certain embodiments, the load may comprise one or more persons (e.g., where device 10 comprises an aerial work platform). Lift 16 is supported by body 12 and is configured for vertical movement relative to body 12 under the control of linear actuators 26. In the illustrated embodiment, lift 16 includes a carriage assembly 36 that is supported on mast 32 and configured for transverse (vertical) movement relative to mast 32 along axis 38 under the control of linear actuators 26. Lift 16 further includes a pair of forks 40 supported on carriage assembly 36 to support the load. In addition to vertical movement along axis 38, carriage assembly 36 may support for-aft movement of forks 40 relative to mast 32 along axis 42 (“reach”), sideways movement relative to mast 32 along axis 44 and rotational movement about one or more of axes 38, 42, 44. The position of lift 16 along and/or about axes 38, 42, 44 may be measured using position sensors that output position signals to controller 30.
Power source 18 provides power, in the form of electrical current, to other components of device 10 including drive motor 20, motor brakes 22, speed sensor 24, linear actuators 26, operator interface 28 and controller 30. Power source 18 may comprise a battery or another conventional energy storage device such as a capacitor.
Drive motors 20 provide a means for causing rotation of wheels 14 and moving device 10 along a floor or the ground. Drive motors 20 may also provide a means for braking rotation of wheels 14 through regenerative braking. It should be understood that the number of motors 20 will vary depending on the type of device 10 and the number of driven wheels 14 on device 10. Each motor 20 comprises an electric motor such as an alternating current motor with a stator and rotor or a brushed or brushless direct current motor. An output shaft of motor 20 may be coupled to an axle supporting one or more wheels 14 through a gear train or another conventional manner. When movement of device 10 is desired, motor 20 causes rotation of wheels 14 in a rotational direction. When braking of device 10 is desired, motor 20 resists further rotation of wheels 14 in that rotational direction and converts the kinetic energy of device 10 into potential energy that may be stored in power source 18.
Drive motor brakes 22 are provided to apply a braking torque to motors 20 and, indirectly, to wheels 14. It should be understood that the number of brakes 22 may vary depending, in part, on the number of drive motors 20 in device 10. Brakes 22 may comprise electric brakes and, in some embodiments, electromagnetic brakes. Brakes 22 may also comprise fluid (hydraulic or pneumatic) brakes. In one embodiment, brakes 22 may comprise spring-set, electromagnetically released brakes that function as an emergency or parking brake. Each brake 22 may, for example, include a friction plate coupled to a shaft of motor 20 and configured for rotation with the shaft, an armature that is biased towards engagement with the friction plate by one or more springs to apply the brake 22 and an electromagnet that, when current is provided to the electromagnet, urges the armature away from the friction plate against the biasing force of the springs to release the brake 22. One of both of the friction plate and armature may include a brake pad made from conventional friction materials. Although an exemplary spring-set, electromagnetically release brake has been described above, in should be understood that brakes 22 may assume a variety of forms including, for example, electromagnetically set, spring-released brakes and brakes employing permanent or residual magnetism to apply and/or release the brake—each of which may be used to implement proportional or service braking of motors 20 as an alternative to, or in addition to, emergency or parking brake functionality.
Speed sensor 24 provides a means for determining the rotational speed of a wheel 14. Sensor may employ either a magneto-resistive or magneto-inductive operating principle and may comprise, for example a Hall effect sensor or a variable reluctance sensor. Sensor 24 may generate a speed signal indicative of a rotational speed of the driven wheel 14 and provide that signal to controller 30 along a conventional communications bus in device 10. Sensor 24 may measure the rotational speed of the driven wheel 14 directly or indirectly through, for example, the rotational speed of an output shaft of a corresponding drive motor 20.
Linear actuators 26 provides a means for raising and lowering lift 16 along axis 38. It should be understood that the number of actuators 26 may vary depending on the type of device 10 and anticipated loads to be lifted by the device 10. In accordance with one aspect of the present teachings, actuators 26 comprise electromechanical linear actuators. Referring now to
Housing 46 provides structural support to other components of actuator 26 and prevents damage to those components from foreign objects and elements. Housing 46 may include multiple members 62, 64. In the illustrated embodiment, member 62 comprise an outer tube housing a portion of screw 48 and nut 50 while member 64 houses another portion of screw 48 and gear train 56. Screw 48 may be supported for rotation within member 64 of housing 46 by bearings 66.
Screw 48 and nut 50 convert rotary motion of actuator motor 54 and gear train 56 to linear motion. Screw 48 comprises a threaded shaft configured for rotation about axis 68 (which may run parallel to axis 38 in
Position sensors 52 are provided to indicate the position of components within actuator 26. Position sensors 52 may indicate the linear position of a component of actuator 26 and may, for example, determine when the nut 50 or rod 70 has reached a predetermined position such as the maximum stroke length of actuator 26 during extension or retraction. Alternatively, position sensors 52 may indicate the rotational position of a component of actuator 26 such as screw 48 or a rotating component of motor 54 or gear train 56. In some embodiments, position sensors 52 may comprise, for example, potentiometers or linear non-contact sensors including Hall effect sensors. In one embodiment, position sensors 52 may comprise limit switches that are actuated in response to movement of the nut 50 or rod 70. In particular, when the nut 50 or rod 70 reaches a predetermined position, the state of the limit switch changes and the switch generates a signal that is transmitted to controller 30 indicating that the nut 50 or rod 70 is located at the predetermined position. In response, controller 30 controls delivery of current to actuator motor 54 and/or actuator brake 58. For example, if the position sensor 52 indicates that the nut 50 or rod 70 has reached maximum stroke length, controller 30 may terminate operation of actuator motor 54 and/or apply actuator brake 58.
Actuator motor 54 is provided to generate torque to cause rotation of screw 48. Actuator motor 54 may also act as a regenerative brake for screw 48 and lift 16 as screw 48 is retracted and lift 16 is lowered with actuator motor 54 converting the kinetic energy of the lift 16 into potential energy that may be stored in power source 18. Actuator motor 54 comprises an electric motor such as an alternating current motor with a stator and rotor or a brushed or brushless direct current motor. Actuator motor 54 may receive current from power source 18 and may be controlled by controller 30.
Gear train 56 is provided to transfer torque output by actuator motor 54 to screw 48. Gear train 56 includes at least one gear coupled to an output shaft of actuator motor 54 and one gear coupled to screw 48. It should be understood, however, that the number and configuration of the gears in gear train 58 may vary depending on the components, operations and capabilities of actuator 26. It should also be understood that actuator 26 may employ a belt drive or other mechanism for torque transfer as an alternative to gear train 56.
Actuator brake 58 provides a parking or emergency brake for actuator motor 54 that is applied to inhibit movement of actuator motor 54, gear train 56, screw 48, nut 50, rod 70 and lift 16 under various operating conditions. Actuator brake 58 may be controlled by controller 30 and may comprise a spring-set, electromechanically released brake that function as an emergency or parking brake. Brake 58 may, for example, include a friction plate coupled to a shaft of motor 54 and configured for rotation with the shaft, an armature that is biased towards engagement with the friction plate by one or more springs to apply the brake 58 and an electromagnet that, when current is provided to the electromagnet, urges the armature away from the friction plate against the biasing force of the springs to release the brake 58. One of both of the friction plate and armature may include a brake pad made from conventional friction materials. Although an exemplary spring-set, electromagnetically release brake has been described above, in should again be understood that brake 58 may assume a variety of forms including, for example, electromagnetically set, spring-released brakes and brakes employing permanent or residual magnetism to apply and/or release the brake—each of which may be used to implement proportional or service braking of motor 54 as an alternative to, or in addition to, emergency or parking brake functionality.
Current sensor 60A provides one means for generating a signal indicative of the weight of a load on lift 16. Current sensor 60A is provided to determine the level of current required by actuator motor 54. Although current sensor 60A is illustrated as a separate element that transmits a signal to controller 30, it should be understood that sensor 60A may form a part of controller 30. In accordance with one aspect of the present teachings, current sensor 60A determines the level of current required by actuator motor 54 as an indication of the weight of the load on lift 16. In particular, the amount of torque required to move lift 16 will, in part, be dependent on the weight of the load on lift 16. Because the amount of torque generated by actuator motor 54 is proportional to the current in actuator motor 54, the current level will be indicative of the weight of the load on lift 16. Baseline or calibration measurements can be obtained before use of device 10 of the current required by actuator motor 54 to raise an unloaded lift 16.
In alternative embodiments actuator 26 may include other means for generating a signal indicative of the weight of a load on lift 16. In one embodiment, actuator 26 may include a linear displacement sensor 60B such as a Hall effect sensor that detects displacement of a component of actuator 26 resulting from compression of one or more elastic members in actuator 26. Actuator 26 may include elastic members such as spring washers of Bellville springs located between a mounting point for actuator 26 and one of the load transmitting components in the actuator 26 such as screw 48. Referring to
Referring again to
Controller 30 provides a means for controlling the operation of drive motors 20, drive motor brakes 22 and linear actuators 26. Controller 30 may comprise a programmable microprocessor or microcontroller or may comprise an application specific integrated circuit (ASIC). Controller 30 may include a memory 72 and a central processing unit (CPU) 74. Controller 30 may also include an input/output (I/O) interface 76 including a plurality of input/output pins or terminals through which controller 30 may receive a plurality of input signals and transmit a plurality of output signals. The input signals may include signals received from speed sensor 24, operator interface 28, position sensors 52, and sensors 60A, 60B, 60C used to generate an indication of the weight of the load on lift 16 while the output signals may include signals transmitted to drive motors 20, drive motor brakes 22, actuators 26, and operator interface 28.
In the illustrated embodiment, a single controller 30 controls the operation of drive motors 20, drive motor brakes 22 and linear actuators 26. Referring to
In accordance with the present teachings, controller 30 (in the embodiment illustrated in
In the above-described embodiments, controller 30 and/or controller 78 determines the weight of the load based on a signal from current sensor 60A (or a value in memory 72 or 80), a linear displacement sensor 60B or a deformation sensor 60C after receiving a brake command. In certain embodiments, however, controller 30 and/or controller 78 may generate control signals for drive motor brakes 22 that preset brakes 22 to apply a particular torque whenever a subsequently issued braking command is received (e.g., from automated emergency braking system in device 10 upon a loss of power in device 10). Controller 30 and/or controller 78 may generate the control signals to motor brakes 22 at any point in time responsive to signals from sensor 60A (and/or values in memory 72 or 80), the linear displacement sensor 60B or deformation sensor 60C to preset the applied torque of the motor brakes 22.
Controllers 30, 78 may further be configured to consider other factors in controlling drive motor 20 and/or wheel brakes 22. For example, controller 30 and/or controller 78 may be configured to control drive motor 20 and/or wheel brakes 22 in response to the weight of the load (e.g., as indicated by the level of current required by actuator motor 54, the displacement of screw 48 of actuator 26 or the deformation or displacement of housing member 64) and the speed of wheels 14 as indicated by speed sensor 24. In particular, controller 30 and/or controller 78 may be configured to increase the braking torque applied by drive motor 20 and/or wheel brakes 22 when device 10 is moving relatively fast and reduce the braking torque when device 10 is moving relatively slow. Controller 30 and/or controller 78 may also be configured to control drive motor 20 and/or wheel brakes 22 in response to the weight of the load and the height of lift 16. In particular, controller 30 and/or controller 78 may be configured to increase the braking torque applied by drive motor 20 and/or wheel brakes 22 when lift 16 is at a relatively low position (and there is a reduced risk that device 10 will tip) and to decrease the braking torque when lift 16 is a relatively high position. Controller 30 and/or controller 78 may also be configured to control drive motor 20 and/or wheel brakes 22 in response to the weight of the load and the direction of travel of device 10. In particular, controller 30 and/or controller 78 may be configured to increase or decrease the braking torque applied by drive motor 20 and/or wheel brakes 22 based on the direction of travel depending on the type of device 10 and the center of gravity of device 10. Although the speed of device 10, the height of lift 16 and direction of travel of vehicle 10 have been described alternatively, it should be understood that any combination of these factors may be used (e.g., with appropriate weighting) together with the weight of the load to determine proper control of drive motor 20 and/or wheel brakes 22.
Controller 30 and/or controller 78 may further be configured to use the weight of the load to perform other functions aside from controlling drive motor 20 and/or wheel brakes 22. For example, in accordance with certain embodiments, controller 30 and/or controller 78 may establish values for various control parameters for device 10 responsive to the weight of the load. These parameter values may, for example, include a maximum speed for device 10, a minimum turn radius for device 10, a maximum allowed height for lift 16 or other values. In accordance with certain embodiments, controller 30 and/or controller 78 may generate and provide information on the operation of device 10 responsive to the weight of the load. For example, in accordance with one embodiment, controller 30 and/or controller 78 may determine an amount of wear in a component of device 10 such as drive motor 20 or drive motor brake 22 responsive to the weight of the load. For example, the wear on friction components of drive motor brake 22 is related to the amount of energy dissipated in brake 22 during a braking event. The amount of energy dissipated in brake 22 is dependent on the speed of device 10 and the mass of device 10. The speed of device 10 can be obtained from speed sensor 24. The mass of device 10 can be obtained from a combination of a stored value indicative of the unloaded weight of device 10 and the measured weight of the load on device 10. Using these values, controller 30 and/or controller 78 can determine the amount of wear on the friction components of brake 22. Controller 30 and/or controller 78 may use this information in a variety of ways including in the control of drive motors 20 and drive brakes 22, establishing operating parameter values for motors 20 and drive brakes 22 and to generate an indication of the amount of wear to either or both of an operator of device 10 through, for example, operator interface 28, and a centralized management system for device 10 through, for example, wireless transmission of a signal indicative of the amount of wear (e.g., for the purpose of predictive maintenance).
A mobile lift device 10 and control system for a brake of the mobile lift device 10 in accordance with the present teachings is advantageous relative to conventional mobile lift devices and brake control systems. In particular, the inventive lift device 10 and brake control system uses a signal generated by the electromechanical linear actuator 26 as an indicator of the weight of the load in order to provide improved control of braking for the driven wheel 14 of the mobile lift device 10. As a result, the braking torque can be varied based on the load and improved control of the mobile lift device during braking is obtained.
While the invention has been shown and described with reference to one or more particular embodiments thereof, it will be understood by those of skill in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
