Patent Publication Number: US-7915752-B2

Title: Apparatus for enabling an aerial lift including a self-disabling interlock

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to a control circuit for enabling an aerial lift member. Specifically, a control circuit for enabling an aerial lift member including an interlock portion and an over ride of the interlock portion including a self-disabling over-ride switch is disclosed. 
     As is known to those skilled in the art, some mobile vehicles have an auxiliary member which may be extended away from the main body portion of the vehicle. For example, aerial lift trucks may include a boom that can be extended upward and can be rotated up to a continuous 360 degrees of rotation; fire trucks may include an extension ladder that, similarly, may be extended upward and rotated about the vehicle; and construction equipment may include a digging member extending away from the front or rear of the vehicle. In each example, the center of gravity of the vehicle changes as the auxiliary member is extended away from or rotated around the vehicle, creating a potential for the vehicle to tip over. 
     Stabilizing members are typically provided on those mobile vehicles having an auxiliary member to prevent the vehicle from tipping over while the auxiliary member is in operation. Such stabilizing members, also known as outriggers, may be extended and retracted. In the retracted position, the stabilizing member is stored, typically adjacent to the body of the vehicle, such that the stabilizing member does not interfere with the mobility of the vehicle. In the extended position, the stabilizing member is positioned away from the body of the vehicle such that the stabilizer pad engages the ground, or other solid surface, to stabilize the vehicle when the auxiliary member is in operation. 
     An interlock, preventing activation of the auxiliary member, is typically provided in order to ensure that the stabilizing members are extended prior to operating the auxiliary member. Typically, the auxiliary member is manually enabled and disabled by an operator, for example by a switch, lever, or push-button. Enabling the auxiliary member engages actuators, such as relays, solenoids, or valves to provide electrical or hydraulic power, as required by the auxiliary member, and permits motion of the auxiliary member. In order to determine whether the stabilizing members are extended, each stabilizing member has a sensor or a switch associated with that stabilizing member indicating whether the stabilizing member is extended. The sensor or switch interlocks activation of the auxiliary member such that it may not be enabled until each of the stabilizing members is fully extended and engaging the ground. 
     However, such an interlock presents potential disadvantages. For example, the mobile vehicle may be parked on a sloped surface or next to a curb on a street. On such surfaces, the stabilizing member may engage the ground yet not be fully extended. Consequently, the sensor on the stabilizing member indicates that stabilizing member is not fully extended and prevents the auxiliary member from operating. Alternately, one of the sensors or stabilizing members may fail and similarly prevent the sensor from indicating that the stabilizing members are extended. As still another example, the mobile vehicle may be in a garage for service. The auxiliary member may need to be operated while in the garage but there may be no room to extend the stabilizing member. In each example, an operator could determine that the auxiliary member is safe to operate but, nevertheless, be prevented from operating the auxiliary member by the interlock. 
     In an attempt to overcome this disadvantage, some mobile vehicles provide an over ride for the interlock system, permitting the operator to determine whether the auxiliary member is safe to operate. However, such over rides are typically a maintained style of switch, such as a toggle or selector switch that remains active until the switch is returned to its previous state. Such an over ride switch may inadvertently be left on by the operator after the operation of the auxiliary member is complete, causing an interlock from the stabilizing members to be ignored the next time the auxiliary member is in use. Alternately, if vehicles are not equipped with an over ride, the operator may install a jumper, or a wire, around the interlock portion of the control in order to permit operation of the auxiliary member. Again, the jumper may inadvertently be left on after operating the auxiliary member, causing the interlock of the stabilizing members to be bypassed at the next operation of the auxiliary member. 
     Therefore, it is desirable to provide an interlock over ride that permits an operator to bypass the interlock during a single operation of the auxiliary member and prevents the bypass from remaining active during subsequent operations of the auxiliary member. 
     SUMMARY OF THE INVENTION 
     Consistent with the foregoing and in accordance with the subject matter as embodied and broadly described herein, a self-disabling interlock over ride is described in suitable detail to enable one of ordinary skill in the art to make and use the invention. 
     The present invention provides a control circuit for enabling an auxiliary member of a mobile vehicle, preferably an aerial boom on an aerial lift truck, having stabilizing members, or outriggers. The control circuit includes a selector switch for enabling the auxiliary member and an interlock portion that may prevent the auxiliary member from being enabled if one of the stabilizing members is not in an operative position. The control circuit further includes an interlock over ride. The interlock over ride may be activated if the enable switch is selecting to enable the auxiliary member. The interlock over ride permits the auxiliary member to be enabled even if the interlock portion is attempting to prevent the auxiliary member from being enabled. The interlock over ride is, in turn, disabled if the enable selector switch removes the enable signal from the auxiliary member. Thus, the interlock over ride permits an operator to bypass the interlock while the auxiliary member remains active and prevents the bypass from remaining active and inadvertently overriding the interlock during subsequent operations of the auxiliary member. 
     In one embodiment of the present invention, an interlock device is provided on a mobile vehicle having an auxiliary member, which extends away from the vehicle, and at least one stabilizing member. The auxiliary member is selectively enabled and disabled by an enabling means, such as a selector switch. An interlock means selectively prevents the auxiliary member from being enabled, and a bypass means selectively over rides the interlock means. The bypass means is reset when the enabling means disables the auxiliary member. 
     Thus, it is a feature of the present invention to provide an interlock over ride that remains active only while the auxiliary member remains active, being reset when the auxiliary member is disabled. 
     In one aspect of the present invention, the interlock means includes a sensor or a switch associated with each stabilizing member. The sensor provides a signal indicating that the stabilizing member is in the operative position. The signal is used to control a relay, and the relays for each of the stabilizing members are connected in series to establish a conductive path. Similarly, the stabilizing member may cause a switch to close when the stabilizing member is in the operative position. Each of the switches may be connected in series to establish a conductive path when all of the stabilizers are in the operative position. 
     As another aspect of the present invention, the bypass means includes a bypass switch and a bypass relay. If the enabling selector switch is set to enable the auxiliary member, the bypass switch may selectively enable the bypass means. The bypass relay provides a conductive path parallel to the conductive path that may be established by the interlock means. 
     Thus it is a feature of the present invention that the interlock means and the bypass means provide alternate conductive paths for enabling the auxiliary member. 
     As still another aspect of the invention, the bypass switch is preferably a momentary switch. The bypass relay is activated to provide the parallel conductive path by pressing the bypass switch when the enabling selector switch selectively enabling the auxiliary member. The bypass relay then remains active until the enabling selector switch selectively disables the auxiliary member. 
     Thus it is another feature of the present invention that the interlock over ride remains enabled throughout the duration of use of the auxiliary member but is reset when the auxiliary member is no longer enabled. 
     In another embodiment, the present invention is implemented in a control circuit for enabling an auxiliary member on an aerial lift truck having an auxiliary member, which extends away from the truck, and at least one stabilizing member, or outrigger, which may be extended from the truck to engage the ground. The control circuit includes a voltage source supplying a de voltage and a first switch connected in series with the dc voltage source. An interlock switch is associated with each of the stabilizing members and closes when the stabilizing member is substantially engaging the ground. The interlock switches are connected in series with each other forming an interlock conductive path. The interlock path is connected in series with the first switch. The control circuit further includes a first actuator connected in series with the interlock path selectively providing power to the auxiliary member of the truck. 
     The control circuit also includes a bypass circuit connected in parallel with the interlock conductive path. The bypass circuit includes a bypass switch connected in series with the first switch and a bypass actuator selectively providing a bypass path parallel to the interlock path between the first switch and the first actuator. The bypass actuator is connected in series with the bypass switch. The bypass circuit also includes a latching signal connected between the bypass path and returning to the bypass actuator such that the actuator remains active until the first switch is opened. 
     These and other objects, advantages, and features of the invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
       Preferred exemplary embodiments of the subject matter disclosed herein are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which: 
         FIG. 1  is a schematic representation of the one embodiment of the present invention; and 
         FIG. 2  is a schematic representation of another embodiment of the present invention. 
     
    
    
     In describing the preferred embodiments of the invention which are illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. For example, the word “connected,” “attached,” or terms similar thereto are often used. They are not limited to direct connection but include connection through other elements where such connection is recognized as being equivalent by those skilled in the art. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The various features and advantageous details of the subject matter disclosed herein are explained more fully with reference to the non-limiting embodiments described in detail in the following description. 
     Referring to  FIGS. 1 and 2 , a control circuit  10  for enabling an auxiliary member of a mobile vehicle having at least one stabilizer member is disclosed. Preferably, the control circuit  10  operates to selectively enable and disable operation of a lift member on an aerial lift vehicle. The control circuit includes a voltage source  50 , preferably a twelve volt dc supply such as a truck battery. A first terminal  52  of the voltage source  50  is connected to ground  48  and a second terminal  54  of the voltage source  50  provides the dc voltage. 
     An enabling means  12 , at least partly, enables and disables the auxiliary member of the vehicle. The enabling means  12  may be a selector switch  20 . Alternately, the enabling means  12  may be a combination of switches  20 , acting in series or parallel as is known in the art.  FIG. 1  illustrates two switches  20  combined in series to create the enabling means  12 . Preferably, a first switch  20  is the ignition switch of the vehicle and a second switch  20  is a power-take-off (PTO) switch, the two switches working in series to enable the lift member. A first terminal  56  of a selector switch  20  is connected in series to the voltage source  50 . A second terminal  58  of the selector switch  20  connects to the interlock means  14  and the bypass means  16 . 
     The interlock means  14  establishes a conductive interlock path  28  connected in series between the second terminal  58  of the selector switch  20  and a first terminal  45  of the first actuator  46 . The interlock means  14  includes at least one sensor  22 . Each sensor  22  is associated with a stabilizer member on the vehicle and provides a signal  24  indicating when the stabilizer is in the operative position. Preferably, each sensor  22  is a limit switch  30  that is closed when the stabilizer member is extended and engaging the ground. Alternately, each sensor  22  may be any suitable sensor, such as a proximity sensor or pressure switch, and may be connected in any suitable manner, such as closing, opening, or providing an analog voltage to a conductive path, as is known in the art. Preferably, the signal  24  from each sensor  22  controls a relay  26  which, in part, opens or closes the interlock path  28 . The output of each relay  26  is connected in series with the other relays  26  such that when each of the stabilizer members is in the operative position the interlock path  28  is established, providing a conductive path between the selector switch  20  and the first actuator  46 . Alternately, each sensor  22  may be directly connected in series with the other sensors  22 , for example if the sensors  22  are limit switches  30 , such that the interlock path  28  is directly established by closing each of the switches  30 . 
     The bypass means  16  establishes a bypass conductive path  44  parallel to the interlock path  28  using a bypass switch  40  and a bypass actuator  42 . The bypass switch is connected in series between the selector switch  20  and a first terminal  60  of the bypass actuator  42 . The bypass switch  40  is preferably a momentary switch, such that the switch  40  only provides a conductive path while it is being activated by an operator. Such a momentary switch typically has a spring-loaded return, such as a spring-return push-button, toggle, or rocker switch. The bypass actuator  42  is preferably a relay which closes a contact to establish the bypass path  44  between the second terminal  58  of the selector switch  20  and the first terminal  45  of the first actuator  46 . A latching signal  62  is connected between the bypass path  44  from the first terminal  45  of the first actuator  46  to the first terminal  60  of the bypass actuator  42 . 
     The first actuator  46  selectively connects the auxiliary member of the vehicle to the dc voltage source  50 . A first terminal  45  of the first actuator  46  is connected to both the interlock path  28  and the bypass path  44 . The first actuator is preferably a relay which closes a contact to establish an auxiliary power path  64  between the dc voltage source  50  and the auxiliary member. 
     In operation, an operator positions the vehicle at a work site and extends the stabilizing members, as required. The stabilizing members may be controlled individually; controlled in pairs, for example front and back or each side; or controlled as one unit. Similarly, the interlock means  14  may selectively permit operation of the auxiliary member if only a front, rear, or side pair of stabilizing members are extended. Alternately, the interlock means  14  may require that all of the stabilizing members are extended before allowing operation of the auxiliary member. Further, the operating mode of the stabilizer members may be selected by another switch which may also be used by the interlock means. 
     When the vehicle has been positioned and the stabilizing members extended, the operator commands the auxiliary member to enable using the enabling means  12 . During normal operation, each of the stabilizing members has been properly extended and the interlock means  14  will establish the conductive interlock path  28  between the selector switch  20  and the first actuator  46 . The first actuator  46  will activate and establish the auxiliary power path  64  between the dc voltage  50  and the auxiliary member. However, if one of the stabilizing members has not been properly extended or some other failure prevents the interlock means  14  from establishing the interlock path  28 , the bypass means  16  may provide an alternate path to enable the auxiliary member. 
     The operator may selectively over ride the interlock in order to enable the auxiliary member by activating the bypass switch  40 . If the selector switch  20  is closed, closing the bypass switch  40  will energize the bypass actuator  42 . The bypass actuator  42  latches itself on by providing a latching signal  62  between the first terminal  45  of the first actuator  46  and the first terminal  60  of the bypass actuator  42 . Therefore, the bypass switch  40  may be opened but the bypass actuator  42  will remain energized. The bypass actuator  42  remains energized until the selector switch  20  is opened, removing the conductive path between the voltage source  50  and the first terminal  60  of the bypass actuator  42 . 
     It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention