Patent Application
20140216853
Not applicable.
Not applicable.
The present invention relates to the field of industrial lift trucks, and more specifically to systems and methods for improved vibration control for lift trucks.
Lift trucks are designed in a variety of configurations to perform a variety of tasks. One problem with lift trucks is that they can oscillate or vibrate about any of the X-axis, Y-axis and Z-axis (see
Another problem seen by lift trucks traveling throughout a facility is that they can encounter debris on the floor and uneven floor surfaces. These can take the form of expansion joints, cracks in the floor surface or man-made objects such as ramps going between buildings or into tractor trailers. Tire irregularities and/or the floor can also cause periodic vibrations that can be transmitted throughout the truck's frame.
The vibrations caused by the floor condition can diminish the effectiveness and/or accuracy of sensory equipment on the truck and may necessitate that the truck be operated at slower speeds to reduce the effects of the floor conditions. Slower operating speeds can equate to an undesirable reduction in overall equipment productivity.
Most previously used methods to dissipate vibrations have only attempted to address longitudinal vibrations, and do not address torsional vibrations. Methods that have attempted to address torsional vibrations add unnecessary complexity to the lift truck by decoupling the mast from the carriage. This adds cost and weight, and further areas for mechanical issues.
If the vibrating motion of the truck can be mitigated or even cancelled, the truck would then be capable of traveling faster without the potential damage to components or loss or degradation of truck data, along with a more comfortable ride for the operator.
What is needed is a lift truck configured to improve mitigation of vibrations about the Z-axis, thereby providing a more comfortable ride for the operator and improving productivity.
Embodiments of the present invention overcome the drawbacks of previous methods by providing systems and methods for improving the vibration control of a lift truck by providing additional stability control features to reduce or eliminate vibrating motion of the truck about the Z-axis. Embodiments of the present invention induce a counter moment to effectively cancel or damp the torsional vibrations, particularly in lift trucks having tall masts and in lift trucks that can provide right angle stacking, for example. The counter moment systems and methods can provide smoother ride characteristics and facilitate improved load handling by providing a more stable ride for the operator.
In one aspect, the present invention provides a system for mitigating torsional vibrations about a Z-axis of a lift truck. The system comprises a tractor unit, with a mast mounted relative to the tractor unit, the mast including a fixed base and a vertically extendable mast section. A vertically movable platform can be attached to the extendable mast section, the platform being vertically movable with the extendable mast section between an upper position and a lower position. A first sensor can be positioned at or near a top of the mast, the first sensor to measure yaw about the Z-axis at or near the top of the mast. A corrective yaw input mechanism can induce a counter moment at or near the fixed base when the measured yaw about the Z-axis at or near the top of the mast exceeds a predetermined value, the induced counter moment used to damp the measured yaw about the Z-axis at or near the top of the mast.
In another aspect, the present invention provides a method for mitigating torsional vibrations about a Z-axis of a lift truck, the lift truck including a mast. The method comprises steps including measuring yaw about the Z-axis at or near a top of the mast; and inducing a counter moment at or near a mast fixed base with a corrective yaw input mechanism when the measured yaw about the Z-axis at or near the top of the mast exceeds a predetermined value, the counter moment used to damp the measured yaw about the Z-axis at or near the top of the mast.
In yet another aspect, the present invention provides a method for mitigating torsional vibrations about a Z-axis of a lift truck. The method comprises steps including monitoring at least one of operator inputs and lift truck parameters; determining if a steering angle is substantially constant; measuring torsional vibrations about the Z-axis in the lift truck; determining if the measured torsional vibrations are at or over a predefined limit; and instructing a corrective yaw input mechanism to generate a corrective yaw input at or near a base of the lift truck, the corrective yaw input for reducing the measured torsional vibrations.
The foregoing and other objects and advantages of the invention will appear in the detailed description which follows. In the description, reference is made to the accompanying drawings which illustrate preferred embodiments.
The invention may be embodied in several forms without departing from its spirit or essential characteristics. The scope of the invention is defined in the appended claims, rather than in the specific description preceding them. All embodiments that fall within the meaning and range of equivalency of the claims are therefore intended to be embraced by the claims.
The various aspects of the invention will be described in connection with improved vibration control of industrial lift trucks. That is because the features and advantages that arise due to embodiments of the invention are well suited to this purpose. Still, it should be appreciated that the various aspects of the invention can be applied to achieve other objectives as well.
While the description of embodiments of the invention and the accompanying drawings generally refer to a man-up orderpicker style lift truck, it is to be appreciated that embodiments of the invention can be applied to control unwanted torsional vibrations in any lift truck configuration. Other vehicles that can benefit from embodiments of the invention include a reach truck, a high-lift truck, a counterbalanced truck, and a swing-reach truck, as non-limiting examples.
Referring to
The source of the torsional vibrations can be floor irregularities, operator steering inputs, and/or operator movement between the carriage 34 and a mezzanine or rack, for example. Embodiments of the invention can measure and/or compare either the yaw or the yaw rate at or near the top of the mast 60 to the yaw or yaw rate at or near the base of the mast 62, or anywhere in between. Embodiments of the invention can address the measured torsional vibrations by imposing a counter moment, such as at or near the base of the mast 62, by introducing a corrective counter yaw input. Because the relative stiffness of the mast 32 is finite in all axes, the yaw at or near the top of the mast 60, for example at the carriage 34 when in a raised position 42, is not necessarily equal to the yaw at the tractor unit 30. The difference between the two yaw measurements can be a function of several parameters and operating conditions, including mast height, mast stiffness and the load 36 on the forks 40. When the carriage 34 begins to vibrate torsionally, the relative yaw or yaw rate between the top of the mast 60 and the tractor unit 30 can be measured and an appropriate corrective counter yaw input can be applied to the lift truck 20 through a corrective yaw input mechanism. The corrective yaw input mechanism can introduce yaw corrections at or near the truck frame 46 and/or the base of the mast that can induce a counter yaw moment to effectively cancel or damp torsional vibrations at or near the top of the mast 60 and along the mast 32. The construction can vary according to corrective yaw input mechanism.
Referring to
Referring to
In some embodiments, a variety of actuators 92 are contemplated for use with the invention. For example, small hydraulic cylinders with a rapid response profile are available. Other suitable actuators would be known to one of skill in the art.
Referring to
In use, if while traveling at an elevated height, for example, the carriage 34 begins to vibrate torsionally, the controller 76 can implement a corrective yaw control algorithm 130 that can command at least one of or combinations of the corrective yaw input mechanisms 70, 90, 110 to induce at least one counter moment of appropriate magnitude to damp or cancel the torsional vibrations. The torsional vibrations at or near the top of the mast 60 and at or near the base of the mast 62 can be monitored by at least one yaw or yaw rate sensor 132 and 134 respectively. In some embodiments, a sensor 132 can be positioned at or near the top of the mast 60, and another sensor 134 can be placed at or near the base of the mast 62. Each sensor 132 and 134 can provide movement feedback to the controller 76.
In some embodiments, a variety of different sensors are contemplated for use with embodiments of the invention. For example, a variety of gyroscope configurations are available, such as a solid state Micro-electromechanical Systems (MEMS) gyroscope. There are also several other types of gyroscope sensors or combinations of sensors that can replace a true gyroscope. In other embodiments, the torsional vibrations of the lift truck could be sensed by differential accelerometers, such as two Z-axis accelerometers with one mounted at or near the top of the mast 60 and one at or near the base of the mast 62. For vibrations about the Z-axis 50, the difference between the Z-axis acceleration at the top and bottom can indicate a vibration is happening. Also, torsional vibrations can be measured by mechanical devices used as sensors. For example, compression or expansion of springs at or near the top of the mast 60 and at or near the base of the mast 62 could be measured by any type of proximity sensor.
Referring to
In some embodiments, the time required to move through the corrective yaw control algorithm 130 can be extremely short. The controller 76 on board the lift truck 20 can run through the corrective yaw control algorithm 130 many times a second, for example. In this way, an operator input 152 such as a change in speed or steering can change the lift truck motion and seconds later, or less, the counter yaw input 150 can be back to reducing the undesirable torsional motion.
Referring to
The corrective yaw control algorithm 130 can start with an initialization process indicated as KEY ON at process block 170. At KEY ON, the algorithm 130 can initialize counters and check sensors, for example. Next, at process block 172, operator inputs 152 and/or lift truck parameters 140 can be monitored. For example, in some embodiments, when the operator 56 touches a brake pedal or accelerator (neither shown), a speed control 156 can be shut down. The corrective yaw control algorithm 130 can at decision block 174 determine if the steering angle, for example, is close to constant and the operator 56 is making only small operator inputs 152. For example, the operator 56 has stopped trying to adjust steering, or wire guidance is ON and the wire guidance system 160 has stopped making large changes in steering angle. If operator inputs 152 and/or lift truck parameters 140 are still changing, the corrective yaw control algorithm 130 can continue to monitor the operator inputs 152 and/or lift truck parameters 140 at process block 172.
At process block 176, the corrective yaw control algorithm 130 can analyze the lift truck 20 motion to measure, for example, any of amplitude, frequency, phase and decay rate of several torsional vibrations using at least one of the sensors 132, 134. The corrective yaw control algorithm 130 can determine if the torsional vibrations are increasing or decreasing. Note that this analysis may be running as a subroutine in the background. This analysis of the lift truck motion can be revised when the lift truck 20 is traveling in a straight line for some time period. This is because the use of steering to induce counter yaw moments can be more effective when the truck 20 has been traveling in a straight line for some time period, e.g., when wire guidance is being used. Revising the analysis can be used to prevent the corrective yaw control algorithm 130 from attempting to modify an operator intended steering input. At decision block 180, the corrective yaw control algorithm 130 can determine if the amplitude, for example, of a vibration, yaw for example, is large enough, e.g., over a predefined limit, or is increasing instead of decaying. If not, the corrective yaw control algorithm 130 can continue to monitor the operator inputs 152 and/or lift truck parameters 140 at process block 172. If the torsional vibration is over a predefined limit, or is increasing instead of decaying, then at process block 182, the corrective yaw control algorithm 130 can instruct any or all of the corrective yaw input mechanisms 70, 90, 110 to generate a counter yaw input 150 to reduce or eliminate the torsional motion the operator can feel. In some embodiments, the corrective yaw control algorithm 130 can continue to generate a counter yaw input 150 until an operator input 152 and or operating characteristics 154 affect the corrective yaw control algorithm 130, such as at decision block 184. Or, if the measured lift truck parameters 140 does not respond to the counter yaw input 150, the corrective yaw control algorithm 130 can STOP at process block 186 and can set a fault code, for example.
In some embodiments, control of torsional vibrations can also be managed using modifications of acceleration and velocity, such as can be done with software that optimizes truck speed at elevations over a full range of heights and load weight conditions, such as the IntelliSpeed system by Raymond Corporation of Greene, N.Y., which can limit lift truck 20 speed at a predefined height. If the operator 56 commands a steering input that the lift truck model 144 predicts would tend to initiate a torsional vibration, the controller 76 can augment the lift truck acceleration and/or velocity so as to minimize any undesirable torsional response. In this way, the controller 76 can also be acting to prevent torsional vibrations before they occur.
In some embodiments, the torsional control strategy can also be applied in conditions where the operator 56 is commanding a steady-state steering input. If, during such an event, the sensors 132, 134 detect an undesirable relative torsional vibration between the carriage 34 and the tractor unit 30, the controller 76 can augment the steering input to induce a counter yaw input 150 to damp or cancel the relative torsional vibration. The corrective counter yaw input 150 to the steering can be small in magnitude such that it may not alter the intended path of the lift truck 20.
As described above, embodiments of the invention create a counter yaw moment at the lift truck level to induce counter moments at or near the base of the mast 62 that can damp or cancel torsional vibrations at or near the top of the mast 60. It is to be appreciated that there can be other ways of achieving this counter yaw moment that have not been described here but should still be considered within the scope of the invention. For example, one such alternate can be for lift trucks that have a moveable mast, in such lift trucks, the hydraulic actuators that are used to move the mast can be used to induce a counter yaw input by commanding the actuators independently of one another in such a way that a counter moment is created. The same is true for lift trucks that have a tiltable mast. The tilt actuators can be used to induce counter yaw moments.
Embodiments according to the invention provide several benefits and advantages that cannot be obtained in existing truck configurations. For example, embodiments of the invention enable a lift truck 20 to stay generally level instead of rocking due to uneven floors. This can be beneficial to the operator standing on the lift truck because a vibrating lift truck can increase operator fatigue. In lifting loads onto or off of high racks or stacks, embodiments of the invention can lock one or more load wheels and/or both the left and right casters to make the mast more stable and stay vertical. Notably, the invention detects and stops the torsional vibrations while other known lift truck stabilization designs do not detect and stop torsional vibrations.
The foregoing has been a detailed description of illustrative embodiments of the invention. Various modifications and additions can be made without departing from the spirit and scope thereof. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. For example, any of the various features described herein can be combined with some or all of the other features described herein according to alternate embodiments. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.
Finally, it is expressly contemplated that any of the processes or steps described herein may be combined, eliminated, or reordered. In other embodiments, instructions may reside in computer readable medium wherein those instructions are executed by a processor to perform one or more of processes or steps described herein. As such, it is expressly contemplated that any of the processes or steps described herein can be implemented as hardware, software, including program instructions executing on a computer, or a combination of hardware and software. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this invention.
