Patent Grant
7617018
Not Applicable
1. Field of the Invention
This invention relates generally to a method and apparatus for increasing platform attitude adjustment range for platforms supported by jacks of a given stroke length.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
There are a wide variety of commercial and industrial applications requiring mobile platforms that can be aligned relative to Earth's gravity (true level) by a known angle, or set of angles. The platforms are mobile and are often self-propelled, allowing them to be easily moved to various locations on the Earth's surface. However, once at a given location the platform must be supported and aligned relative to Earth's gravity before operating in its intended capacity. Examples of such platforms include: heavy industrial equipment, cranes, cherry pickers, and recreational vehicles.
The support and alignment of the platform is often accomplished through the use of jacks attached at different positions around the platform. The jacks may be extended to contact the ground, creating a rigid support base for the platform. By extending and retracting specific jacks, the platform may be aligned to at any angle allowed within the mechanical limits of the platform and jacks. The jacks may be hydraulically driven, or may be driven by DC electric motors.
With the advent of these platforms came the need for systems that can control jack movement (extension and retraction) and automate the task of bringing a platform to a known desired attitude. (Although, in the art, these systems are sometimes referred to as “mobile platform automatic positioning systems”, this document will refer to them as mobile platform automatic attitude adjustment systems, or just “platform attitude adjustment systems” for short. This is because the word “positioning” has connotations more closely related to translation of a body through space rather than the adjustment of the attitude of a body “in-place.” This document uses the word “system” to refer simultaneously to both an apparatus and a process (or method) carried out by that apparatus.)
Recent improvements in sensor technology, combined with the falling prices of semiconductors and microprocessors, are advancing the state-of-the-art in platform attitude adjustment systems. Where, in the past, jack movement was coordinated through the use of discrete circuitry and limited feedback, today it is known for computer processors to use new sensor technologies and advanced algorithms to adjust platform attitudes faster, safer, and more accurately than before. Today's systems are several orders of magnitude more sophisticated and powerful than their predecessors, allowing for unprecedented levels of control and reliability in their operation, but are configured to operate only hydraulically-actuated jacks.
When using jacks to adjust the attitude of a platform, the platform's total range of motion depends mainly on the distance between the jacks, and the total stroke lengths of the jacks. A platform attitude adjustment system cannot position or change the attitude of a platform beyond the point where all jack stroke has been used up.
The diagrams shown in
The following parameters are used to trigonometrically describe the total attitude adjustment capability of a platform positioning system:
If one jack uses up its entire stroke and the other remains stationary, the largest angle (θ) through which the platform may be tilted in the axis of the two jacks is calculated using the following equation:
When designing a platform attitude adjustment system, the jack stroke and placement must be carefully chosen to ensure that the system can move a supported platform through a desired range of attitudes. In most mobile platform attitude adjustment applications, the amount of distance between supporting jacks depends primarily on platform geometry and is not likely to be adjustable. The only variable a designer is generally free to modify with regard to the selection and arrangement of jacks for a given mobile platform application is in the stroke lengths of the jacks. To reduce the cost of the jacks in a platform attitude adjustment system, jacks should be selected that have the shortest stroke lengths possible. However, the jack stroke lengths must be long enough to ensure that the jacks are able to move the platform through a predetermined desired range of attitudes.
It is known for mobile platform automatic attitude adjustment systems to include controllers programmed to coordinate jack movement. For example, U.S. Pat. No. 5,143,386 issued 1 Sep. 1992 to Uriarte, discloses a mobile platform attitude adjustment system that includes a plurality of jacks supporting a platform and powered by respective electric jack motors. A controller is connected to each of the jack drive mechanisms and is programmed to adjust the attitude of the platform by controlling the operation of the jacks. The controller of the Uriarte system is further programmed to coordinate the operation of the jacks as the jacks are adjusting the attitude of the platform. More specifically, the controller adjusts individual jack speeds in accordance with which part of the platform is lowest. However, a mobile platform attitude adjustment system constructed according to the Uriarte patent is unable to increase the range of attitudes through which a platform can be adjusted for a given jack stroke length.
What is needed is a mobile platform attitude adjustment system that coordinates jack actuation in such a way as to increase the range of attitudes through which a platform can be adjusted for a given jack stroke length. This would allow jacks of a shorter stroke length to be selected when designing or adapting a mobile platform attitude adjustment system to suit a given application.
According to the invention, a platform attitude adjustment augmentation apparatus is provided for increasing attitude adjustment range for platforms supported by jacks of a given stroke length. The apparatus includes jacks configured to support a platform at spaced-apart locations and jack drive mechanisms drivingly connected to the respective jacks. A controller is connected to each of the jacks through their respective jack drive mechanisms and is programmed to adjust the attitude of a platform by controlling the operation of the jacks and coordinating their movement as the jacks are adjusting platform attitude. The controller is further programmed to coordinate the movement of the jacks by selecting and commanding at least one of the jacks to retract and selecting and commanding at least one other of the jacks to extend to increase the range of possible platform attitudes for a given jack stroke length.
According to another aspect of the invention the controller is programmed to coordinate the movement of the two selected jacks by commanding one of the selected jacks to retract while the other of the selected jacks is extending. This allows the apparatus to achieve a desired platform attitude more quickly.
According to another aspect of the invention the controller is configured to identify and select which jack is best positioned to achieve a desired attitude by being driven in extension, and to identify and select which jack is best positioned to augment the achievement of a desired platform attitude by being driven in retraction.
According to another aspect of the invention the controller is configured to identify and select which jack is best positioned to speed the achievement of a desired platform attitude by being driven in retraction.
According to another aspect of the invention the controller is programmed to time-limit the movement of the retracting jack to prevent the retracting jack from retracting too far and losing contact with the ground.
According to another aspect of the invention the jack drive mechanisms include direct-drive DC electric jack motors configured to drive the jacks in extension and retraction.
The invention also includes a method for increasing platform attitude adjustment range for a platform supported by jacks of a given stroke length. According to this method one can increase platform attitude adjustment range by determining and selecting, from a plurality of jacks supporting a platform, a first jack of the plurality of jacks that needs to be extended to achieve a desired platform attitude and determining and selecting a second jack of the plurality of jacks that, if retracted, will augment the achievement of the desired platform attitude. The first jack is commanded to extend and the second jack is commanded to retract, thereby increasing the range of attitude adjustment for a given jack stroke length in an axis of tilt defined between the first and second jacks.
According to another aspect of the inventive method, the step of determining a first jack includes selecting a jack that is closest to a portion of the platform that needs to be raised the greatest distance to achieve the desired platform attitude.
According to another aspect of the inventive method, the step of determining a first jack includes determining current platform attitude by analyzing signals from a tilt sensor supported on the platform and comparing current platform attitude to the desired platform attitude.
According to another aspect of the inventive method, the step of determining a second jack includes selecting a jack that is closest to a portion of the platform that can best augment the achievement of a desired platform attitude by being lowered.
According to another aspect of the inventive method, the step of commanding the second jack to retract includes commanding the second jack to retract while the first jack is extending to more rapidly achieve a desired platform attitude.
According to another aspect of the inventive method, the method includes the additional steps of determining a base period, determining a pulse portion of each base period during which the second jack is driven in retraction, and determining a maximum number of pulses for which the second jack can be driven in retraction without causing the second jack to lose ground contact. During the step of commanding the first jack to extend, a cycle counter configured to count the pulses is reset and a time counter is started. The second jack is commanded to start retracting and the time counter is restarted once the time counter reaches a time value equal to the difference between the base period and the pulse. If, when the time counter value equals the pulse value the cycle counter value is less than the maximum number of pulses, the cycle counter is incremented, the second jack is disabled, and another base period is initiated by returning to the step where only the first jack is driven in extension and the time counter is started. The second jack is commanded to start retracting again once the time counter again reaches a value equal to the difference between the base period and the pulse. If, when the time counter value equals the pulse value the cycle counter value is greater than or equal to the maximum number of pulses, the cycle counter is incremented and the second jack is disabled for the remainder of the time that the first jack is driven in extension to prevent the second jack from retracting too far and losing contact with the ground.
These and other features and advantages of the invention will become apparent to those skilled in the art in connection with the following detailed description and drawings, in which:
In this document the term “platform” refers to a body, such as the one shown at 10 in
A platform attitude adjustment augmentation apparatus for increasing platform attitude adjustment range for platforms supported by jacks of a given stroke length is generally indicated at 20 in
As is also shown in
As is further shown in
The controller 23 is capable of sending control signals 32 to the jacks 12 through a first I/O port 34, a relay control 36, and respective H-bridge relays 38. The controller 23 is also capable of sending control signals 40 to the dual-axis tilt sensor 18 through a second I/O port 42. The controller 23 includes a central processing unit 44, a software-implemented digital signal processor 46, and control algorithms 48. A battery 50 provides electrical power to the jacks 12 through the H-bridge relays 38 as well as to the controller 23.
The controller 23 is programmed to adjust the attitude of a platform 10 by controlling the operation of the jacks 12 and coordinating their movement. The controller 23 is further programmed to coordinate the movement of the jacks 12 in a given axis of tilt X, Y by selecting and commanding one jack 12 of the plurality of jacks to retract and selecting and commanding another to extend so as to increase the range of possible platform attitudes for a given jack stroke length. As shown in the diagram of
On average, a system tilt capability can be increased by a factor of 1.5× using this method. For small tilt angles, the system capability is increased by nearly a factor of two.
The platform attitude adjustment augmentation apparatus 20 includes a jack drive mechanism 60 for each jack. Each of the jack drive mechanisms 60 includes one of the jack motors 14 and drivingly connects that jack motor 14 to one of the jacks 12. The controller 23 is connected to each of the jack drive mechanisms 60 and is programmed to drive each jack 12 in extension by causing that jack's associated jack motor 14 to operate in one direction and to drive each jack 12 in retraction by causing its jack motor 14 to operate in the opposite direction. The jack motors 14 of the present embodiment are direct-drive DC electric motors. In other embodiments, any suitable type of electric motor may be used.
The controller 23 is programmed to coordinate the movement of the jacks 12 by commanding at least one of the jacks 12 or sets of jacks to retract while commanding at least one other of the jacks 12 or sets of jacks to extend. The controller 23 is programmed to identify and select whichever of the jacks 12 or sets of jacks is best positioned to achieve or speed the achievement of a desired attitude by being driven in extension. The controller 23 is also programmed to identify and select whichever of the jacks 12 or set of jacks is the “opposite” of the jack or set of jacks identified and selected for extension, i.e., the jack or set of jacks best positioned to augment the achievement of a desired platform attitude by being driven in retraction. To prevent the retracting or “opposite” jack or set of jacks from retracting too far and losing contact with the ground the controller 23 is also programmed to time-limit the movement of the retracting jack or set of jacks.
In practice, augmenting or increasing platform attitude adjustment range for platforms 10 supported by jacks 12 of a given stroke length can be accomplished by first taking the preliminary steps of first determining current platform attitude by measuring the actual attitudes of the X and Y axes based on signals received from the tilt sensor 18 as shown in action step 64 of the process flow chart of
Loss of ground contact by the retracting jack or set of jacks may be prevented by preliminarily determining a base period (Tperiod), determining a retraction pulse portion (Tpulse) of each base period during which the second jack or set of jacks is to be driven in retraction, and determining a maximum number of cycles (Kmax) during which the second jack or set of jacks can be driven in retraction for the pulse period without causing the second jack to lose ground contact. These values are stored in the apparatus 20, preferably in non-volatile reprogrammable memory 35 such as EEPROM to allow the parameters to be updated to reflect more accurate or recent calculations, or changed to adapt to different applications or conditions. This allows the latest parameter values to be programmed into the product at the end of the production line and/or modified after the product is built. This method is typically implemented on new products where it's advisable to allow for parameter changes that may be implemented during early production. It's also useful to implement this method during the development phase of a product, when parameters are being determined and change daily. However, some or all of the parameters may alternatively be hard-coded into program ROM. This is a lower cost solution that may be implemented on mature products for which parameter values have not changed for a long period of time and are not expected to change in the foreseeable future.
When an attitude adjustment process is started the controller 23 initiates an augmentation process using the data obtained in the preliminary steps described above. The augmentation process, which is shown in
After the time counter and cycle counter are initially set to zero, if the first jack or set of jacks is determined to be active at decision point 94 then the time counter is incremented by one time unit as shown at action point 96. If the cycle counter value is determined to be less than the maximum number of cycles (Cycles<Kmax) at decision point 98, and the time counter measures an elapsed time value less than or equal to the difference between the base period and the pulse period (Timer≦Tperiod−Tpulse) at decision point 100, then the pulse portion of the period has not yet been reached, the second jack or set of jacks remains disabled as shown at action point 102, and the process returns to the point, decision point 94, where the controller determines whether the first jack or set of jacks is active. If the cycle counter value is less than the maximum number of cycles (Cycles<Kmax) at decision point 98, but the time counter measures an elapsed time value greater than the difference between the base period and the pulse period (Timer>Tperiod−Tpulse) at decision point 100, then the pulse period has begun and the second jack is activated in retraction as shown at action point 102. The second jack or set of jacks remains activated for the duration of the pulse period, i.e., as long as the time counter measures an elapsed time value less than or equal to the base period value as determined at decision point 104, and as long as the first jack or set of jacks remains active as determined at decision point 102.
Once the time counter measures an elapsed time equal to the base period value (Timer=Tperiod) at decision point 104 the time counter is reset to zero and the cycle counter is incremented as shown at action point 106. The process then returns to the point, decision point 94, where the controller determines whether the first jack or set of jacks remains active. If, when returning to decision point 94 the controller finds that the first jack or set of jacks is no longer active, the time counter and cycle counter are both reset to zero at action point 92. If, instead, when returning to decision point 94 the first jack or set of jacks is determined to still be active, another base period is imitated by incrementing the timer at action step 96 and commanding the second jack or set of jacks to start retracting again once the time counter again reaches a value equal to the difference between the base period and the pulse (Timer=Tperiod−Tpulse) as determined at decision step 100.
If, upon returning to decision point 94 the first jack or set of jacks is determined to still be active but at decision point 98 the cycle counter value is determined to be greater than or equal to the maximum number of cycles (Cycles≧Kmax), the cycle counter is incremented and the second jack or set of jacks is disabled at action point 108 for the remainder of the time that the first jack or set of jacks is driven in extension to prevent the second jack or set of jacks from retracting further.
By employing a platform attitude adjustment system constructed according to the invention, for a given attitude range requirement, the jack stroke length requirement can be significantly reduced, resulting in cost savings. In addition, a system constructed according to the invention will, by driving jacks or sets of jacks in opposite directions simultaneously, allow the attitude of a platform to be adjusted faster since a larger tilt angle is covered over a given amount of time.
This description is intended to illustrate certain embodiments of the invention rather than to limit the invention. Therefore, it uses descriptive rather than limiting words. Obviously, it's possible to modify this invention from what the description teaches. Within the scope of the claims, one may practice the invention other than as described.
This application claims priority from provisional Application No. 60/619,768, filed Oct. 18, 2004, which is incorporated by reference.
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