Abstract:
Automated systems and methods control the velocity of the extension arm of a reach carriage. In particular, the extension arm is allowed to operate at full velocity when it is not approaching its extension or retraction limits. At the limits, the extension arm is gradually slowed to a stop. A sensing apparatus includes a sensor and a marker that moves with the movement of the extension arm. The marker moves into and out of the sensor&#39;s range, causing the sensor to generate a position signal. If the extension arm is nearing its limit, the marker is outside the sensor range. A control unit detects changes in the position signal and slows the extension arm accordingly. The control unit may apply a deceleration profile to cushion the extension arm at its limits.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT CONCERNING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     FIELD OF THE INVENTION 
     The present invention relates to controlling a lift truck reach carriage, and more specifically to using a sensor to control the velocity of a lift truck reach carriage. 
     BACKGROUND OF THE INVENTION 
     Lift trucks, also known as forklifts, are commonly used to raise and position heavy loads on elevated surfaces. Some lift trucks include a reach carriage that extends horizontally away from the mast of the lift truck to “reach” a position that is within the reach carriage&#39;s limit of extension. Such lift trucks are referred to herein as “reach trucks.” Typically, a reach truck&#39;s reach carriage includes a pantographic extension arm connected between the mast and the fork assembly. Extension and retraction of the extension arm is conducted using a hydraulic ram cylinder attached between the mast and a pivot point of the extension arm. The extension arm extends as the cylinder fills with fluid, and retracts as the cylinder empties. 
     Considering that, during operation of the extension arm, the fork assembly may support a load of several tons significantly far off the ground, close control of the extension arm velocity may be needed to avoid abrupt stops at the extension arm&#39;s limits. In particular, it would be advantageous to gradually or incrementally slow the extension arm as it approaches its fully extended or fully retracted positions. This may be done manually by the operator if the reach truck has operator controls therefore. However, this method may be imprecise, and the extension arm position could be ignored or miscalculated by the operator. 
     Previous approaches for controlling the reach carriage velocity include continuous positional feedback encoders and specially-machined hydraulic ram cylinders, both of which have significant drawbacks. Encoders track the position of the extension arm with a continuously-operating servo motor, and provide position data to the reach truck&#39;s electrical systems to control flow rate into and out of the cylinder. Encoders add significant manufacturing cost, contributed by both the cost of the encoders themselves and the cost of designing mechanical and electrical operations to include the encoders. Encoders are also subject to wear and damage due to their continuous operation, and add replacement costs. Specially-machined hydraulic ram cylinders endeavor to control the flow rate of fluid into the cylinder with permanent contained structures. These devices also carry a high cost, and further may be significantly more complex than a typical hydraulic ram cylinder. The complexity invites manufacturing defects and inconsistencies, as well as machine surface and linkage failures due to relatively poor tolerance. 
     It would therefore be desirable to incorporate automated systems and methods to control the velocity of the reach carriage without adding significant cost and complexity to the reach truck. 
     SUMMARY OF THE INVENTION 
     The invention overcomes the drawbacks of previous reach carriage control systems by detecting a range of positions of the extension arm and providing responsive hydraulic acceleration or deceleration without additional moving or specially-machined parts. 
     The invention provides systems and methods of controlling the velocity of the reach carriage using a sensor that senses the proximity to the sensor of a marker, wherein one or both of the sensor and marker move with the movement of the extension arm. The sensor provides a position signal to a control unit, the position signal indicating whether the extension arm is approaching its extension or retraction limit. Based on the position signal, the control unit may apply or release automated control of the reach carriage velocity. The control module may employ an acceleration profile to gradually speed up the extension of the reach carriage and/or a deceleration profile to gradually slow the reach carriage to a stop. 
     In one embodiment, a velocity control device for a reach carriage having an extension arm comprises: a sensing apparatus configured to detect when the extension arm is approaching at least one of an extension limit and an retraction limit, and to transmit a position signal, the sensing apparatus comprising: a sensor that generates the position signal; and a marker configured to move into and out of a range of the sensor as the extension arm extends and retracts; and a control unit configured to receive the position signal and to slow the extension arm to a stop depending on the position signal. 
     In another embodiment, in a reach carriage having a carriage frame and a pantographic extension arm attached to the carriage frame and driven by a hydraulic ram cylinder attached to the carriage frame, the extension arm, and a hydraulic pump, a velocity control device for the extension arm, the velocity control device comprises: a sensing apparatus comprising: a sensor attached to a clevis on the carriage frame, the sensor having a range and generating a position signal when the sensor is activated; and a marker that activates the sensor when the marker is in the range of the sensor, the marker being attached to a tang of the hydraulic ram cylinder, the tang cooperating with the clevis, and the marker rotating through an angular range, within which the sensor range is disposed, as the extension arm linearly extends and retracts; and a control unit operatively connected to the sensor and the hydraulic pump and configured to receive the position signal and to instruct the hydraulic pump to reduce or increase a flow rate to the cylinder depending on the position signal. 
     In yet another embodiment, a method of controlling the velocity of an extension arm in a reach carriage, the method comprises: as the extension arm is being driven by an actuator, receiving a position signal from a sensing apparatus comprising: a sensor that generates the position signal; and a marker configured to move into and out of a range of the sensor as the extension arm extends and retracts; determining from the position signal whether the extension arm is approaching its extension or retraction limit; if the extension arm is approaching its extension or retraction limit, instructing the actuator to gradually reduce an actuation speed; and allowing the extension arm to be driven at full velocity if the extension arm is not approaching its extension or retraction limit. 
     To the accomplishment of the foregoing and related ends, the embodiments, then, comprise the features hereinafter fully described. The following description and the annexed drawings set forth in detail certain illustrative aspects of the invention. However, these aspects are indicative of but a few of the various ways in which the principles of the invention can be employed. Other aspects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
         FIG. 1  is a left side view of a reach truck in accordance with this disclosure; 
         FIG. 2  is a top right rear perspective view of an extension arm connectable to a mast in accordance with this disclosure; 
         FIG. 3  is a top left rear perspective view of an extension arm showing a first embodiment of a top-mounted sensing apparatus in accordance with this disclosure; 
         FIG. 4  is a cross-sectional rear perspective view of a portion of the extension arm of  FIG. 3 , taken along line  4 - 4  of  FIG. 3 ; 
         FIG. 5  is a plan view of the sensing apparatus of  FIGS. 3 and 4  showing the angular range of a marker; 
         FIG. 6  is a schematic view of a reach carriage velocity control system in accordance with this disclosure; 
         FIG. 7  is a flow chart of a method of controlling the reach carriage velocity in accordance with this disclosure; 
         FIG. 8  is a cross-sectional right perspective view of a portion of an extension arm with a second embodiment of a top-mounted sensing apparatus in accordance with this disclosure; 
         FIG. 9  is a cross-sectional front left perspective view of a portion of an extension arm with an embodiment of a front-mounted sensing apparatus in accordance with this disclosure; 
         FIG. 10  is a close-up left rear perspective view of a portion of an extension arm with an embodiment of a bearing-and-stud-mounted sensing apparatus in accordance with this disclosure; 
         FIG. 11  is a close-up rear left perspective view of a portion of an extension arm with an embodiment of a scissor-mounted sensing apparatus in accordance with this disclosure; and 
         FIG. 12  is a side view of a portion of an extension arm including a limit switch. 
     
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed. 
     It is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
     Unless specified or limited otherwise, the terms “connected” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. As used herein, unless expressly stated otherwise, “connected” means that one element/feature is directly or indirectly connected to another element/feature, and not necessarily electrically or mechanically. Likewise, unless expressly stated otherwise, “coupled” means that one element/feature is directly or indirectly coupled to another element/feature, and not necessarily electrically or mechanically. Thus, although schematics shown in the figures depict example arrangements of processing elements, additional intervening elements, devices, features, or components may be present in an actual embodiment. 
     The various embodiments of the invention will be described in connection with systems and methods for controlling the velocity of a reach carriage having an extension arm that extends and retracts with respect to a mast of a reach truck. That is because the features and advantages of the invention are well suited for this purpose. Still, it should be appreciated that the various aspects of the invention can be applied to other vehicles and in other industries and processes capable of utilizing an extending arm, particularly a pantograph. 
     Referring now to the Figures, and more particularly to  FIG. 1 , the general arrangement of a representative vehicle, such as a reach truck  20 , incorporating a reach carriage  24  is shown. For simplicity, the detailed description will describe the embodiments associated with the reach truck  20  incorporating the reach carriage  24 . It is to be appreciated that the details of the invention may also be beneficial and adapted for a wide variety of devices and vehicles, including a reach truck where the reach carriage is coupled to a mast  22 , and the mast is configured to extend and retract. Although the reach truck  20 , by way of example, is shown as a standing configuration lift truck, it will be apparent to those of skill in the art that the features of the invention are not limited to vehicles of this type, and can also be provided in various other types of vehicles, including but not limited to, other material handling and lift vehicle configurations. 
     As seen, one embodiment of the reach truck  20  includes an operating unit  21  that may serve as a weighted base for the reach truck  20  and also provides controls to an operator for moving reach truck  20  and operating the reach carriage  24 . The reach truck  20  includes a vertically oriented mast  22  mounted relative to the operating unit  21 . The reach carriage  24  includes an extension arm  25  that connects the mast  22  to a lift assembly  23 , which may comprise one or more forks  26 . The extension arm  25  is illustrated as a double pantographic arm but may be a single pantographic arm (see  FIG. 3 ), or more than a double pantographic arm. Other known extension mechanisms are contemplated, including drive systems, rails, slides, glides, gears, cables, and the like. The extension arm  25  can extend and retract in other fashions, such as by telescopic operation. Manipulation of the controls by the operator may cause various motors, wheels, cables, pneumatic or hydraulic pistons, and other mechanical components to raise and lower the reach carriage  24  along the mast  22 , and to extend and retract the extension arm  25  with respect to the mast  22 . 
     Referring to  FIGS. 2 and 3 , the extension arm  25  may include a plurality of pivotably interconnected rigid members, referred to herein as studs  30 . A stud  30  may connect to one or more adjacent studs  30  at a midpoint or an endpoint of each stud  30 , at one or both sides of the extension arm  25 , to create a pantograph as is known in the art. A pivot  35  is formed at each attachment point between studs  30 . The extension arm  25  pivotally attaches to a carriage frame  28  of the reach assembly  24 . In some embodiments, the carriage frame  28  can movably attach to and translate vertically along the mast  22 . The extension arm  25  attaches to the carriage frame  28  at a stationary pivot  39  at the top of the extension arm  25  and a translating pivot  40  at the bottom of the extension arm  25 . The stud or studs  30  attaching at the translating pivot  40  may be attached to a wheel  45  disposed within a vertical channel  50  on the carriage frame  28 . The wheel  45  moves vertically up the channel  50  to extend the extension arm  25  and down the channel  50  to retract the extension arm  25  according to pantographic motion. The top  51  of the channel defines the extension limit of the extension arm  25  and the bottom  52  of the channel defines the retraction limit, provided the reach truck  20  does not include a bumper or another structure for stopping extension and/or retraction. 
     The motion of the extension arm  25  may be mechanically controlled with at least one hydraulic ram cylinder  55 . The cylinder  55  attaches at a proximal end to the carriage frame  28  and at a distal end to an axle  34  attached between the studs  30  that are attached to the carriage frame  28  at the stationary pivot  39 . The cylinder  55  may be attached at one or both ends with a clevis fastener. The carriage frame  28  may include an integral clevis  65  that cooperates with a tang  60  on the cylinder  55  to allow rotation of the cylinder  55  around a clevis pin  62  (see  FIG. 4 ). The tang  60  may be bolted, welded, or otherwise attached to the cylinder  55  as is known in the art. The cylinder  55  may be attached to a fluid supply hose (not shown) connected to a hydraulic pump (not shown) that fills and empties the cylinder  55  to create the pressure differentials that operate the ram  56  of the cylinder  55  to extend or retract the extension arm  25 , as is known in the art. According to the present disclosure, the cylinder  55  may be any hydraulic or pneumatic cylinder suitable for operating the reach carriage of a reach truck. 
     Referring to  FIGS. 3 and 4 , a first embodiment of a sensor apparatus  64  may include a marker  70  mounted on the tang  60 , the marker  70  cooperating with a sensor  80  mounted on the clevis  65 . The marker  70  may be a solid structure attached to or integral with the tang  60  and projecting outward from the tang  60  into the space between the prongs  66 ,  68  of the clevis  65  above the tang  60 . The marker  70  may be attached to the tang  60 , such as by welding, threaded cooperation, or friction fit, but such non-integral attachments introduce a tolerance risk due to the possibility of the marker  70  becoming loose or misaligned. Preferably, therefore, the marker  70  is integral with the tang  60 , such as by machining the tang  60  and marker  70  from a single piece of bar stock, in order to maximize tolerance control. 
     In one embodiment, as illustrated, a mounting aperture  72  may be provided in a prong  66  of the clevis  65  and the sensor  80  may be mounted therein. The mounting aperture  72  may be positioned so that the sensor  80  cooperates with the marker  70 , in that the marker  70  passes through the sensing range R of the sensor face  82 . In some embodiments, due to the restrictive tolerances of the machined parts, the sensor face  82  can be substantially planar and can be flush with the inner surface  67  of the prong  66  in which the sensor  80  is mounted. The sensor  80  may be a physical sensor, e.g., a limit switch, or a proximity sensor, such as a magnetic or capacitive sensor that reacts to the presence of ferrous metals within its range R and without contact. The marker  70  may therefore be a ferrous metal or another material to which the sensor  80  reacts. In some embodiments, the marker  70  may be the same material as the cylinder  55 , and the range R of the sensor  80  may be sufficiently short so as not to undesirably detect the cylinder  55  instead of the marker  70 . The sensor  80  may further include a transmission cable  85  that transmits a signal to a control unit  100  as described below. Alternatively, the sensor  80  may wirelessly transmit a signal to the control unit  100 . 
     In some embodiments, the sensor  80  can be inactive when the marker  70  is not in the sensor&#39;s range R, and activates upon sensing that the marker  70  is within the range R. The marker  70  may be positioned on the tang  60  so that the marker  70  is forward of the sensor  80  range R when the extension arm  25  is fully or nearly fully retracted, and the marker  70  is rearward of the sensor  80  range R when the extension arm is fully or nearly fully extended. It will be understood that “nearly” full extension or retraction refers to the position of the reach carriage  24  when the marker  70  moves out of the range R of the sensor  80  in either direction. This position may be configured by the operator using a software configuration tool as described below. A default position may be between about 4 and about 8 inches away from the fully extended or retracted positions, although other positions are contemplated, and can depend on the application and the extension arm  25  configuration. A default position may also depend on the weight of the load and the maximum velocity of the reach carriage  24 , for example. As the cylinder  55  pressurizes and extends the extension arm  25 , the tang  60  and marker  70  move, e.g., rotate, counter-clockwise around the clevis pin  62 . As the cylinder depressurizes and retracts the extension arm  25 , the tang  60  and marker  70  rotate clockwise around the clevis pin  62 . Thus, in some embodiments, the marker  70  can pass into, through, and completely out of the sensor  80  range R along the full path, referred to as the “stroke,” of the extension arm  25 . The distance that the extension arm  25  travels when the marker  70  is not within the sensor  80  range R is the cushion distance, as described below. 
     Referring to  FIG. 5 , the length of the stroke of the extension arm  25  from a fully retracted position to a fully extended position determines the angular range D through which the marker  70  may travel during all or part of the stroke. In order to provide a cushion of deceleration as the extension arm  25  approaches the fully extended and fully retracted position, the width W of the marker  70  and position of the marker  70  on the tang  60  are configured to leave a first cushion distance C 1  between the proximal edge of the marker  70  and the outer limit of the sensor&#39;s  80  range R, and a second cushion distance C 2  between the distal edge of the marker  70  and the outer limit of the sensor&#39;s  80  range R. The first cushion distance C 1  is traversed by the proximal edge of the marker  70  as the extension arm  25  is retracted to its fully retracted position, and the second cushion distance C 2  is traversed by the distal edge of the marker  70  as the extension arm  25  is extended to its fully extended position. While the marker  70  is traversing the cushion distances C 1 , C 2  as described, the sensor  80  is inactive and the extension arm  25  will undergo a controlled deceleration as described below. 
     Referring to  FIGS. 6 and 7 , a control unit  100  instructs a hydraulic pump  54  to operate the cylinder  55  according to the position signal received from the sensor  80  and one or more operator controls  110 , such as a throttle or stick control. The control unit  100  may be dedicated to control of the cylinder  55 , and therefore only extend or retract the extension arm  28 , or the control unit  100  may be electrically connected to operate other components of the reach truck  20 , such as the carriage frame  28  or the reach truck  20  drive system. The control unit may be a central processing unit or a microprocessor containing software for configuring and operating the reach carriage  24 . The control unit  100  may be configured to operate the extension arm  25  according to the present disclosure. In particular, the control unit  100  may communicate with the sensor  80  to determine if the sensor  80  is active or inactive. The control unit  100  may poll the sensor  80  for its status continuously, at predetermined intervals, or only upon receiving a drive input from the operator controls. Alternatively, the control unit  100  may simply check whether an electrical circuit over a sensor line  105  is complete. If it is not complete, this indicates the sensor  80  is inactive. When the sensor  80  senses the marker  70 , it closes the gate  106  to complete the circuit. It will be understood that the gate  106  illustrated in  FIG. 6  may be outside the sensor  80  or may be part of an integrated circuit within the sensor  80 . In another embodiment, the control unit  100  may passively receive a signal from the sensor  80  indicating the sensor  80  status. 
     While the sensor  80  is active, the control unit  100  may increase the velocity of the extension arm  25  by instructing the hydraulic pump  54  to pressurize or relieve the cylinder  55  at its maximum flow rate. Alternatively, the control unit  100  may apply an acceleration profile to gradually increase the extension arm  25  velocity to full velocity. The acceleration profile may be substantially linear or may have an exponential increase or decay or an s-curve shape, for example. When the sensor  80  deactivates, the control unit  100  may apply a deceleration profile to gradually reduce the flow rate between the hydraulic pump  54  and the cylinder  55 . The deceleration profile may be substantially linear or may have an exponential increase or decay or an s-curve shape, for example, that brings the extension arm  25  to rest over a distance, which is typically between about 4 and about 8 inches as described above but may be configured by the operator. The shape of the acceleration profile and the deceleration profile, and the distance over which they can be applied may be the same or different, and may be modified using a software configuration tool. 
     The control unit  100  may further be configured to store, or retain in memory, the previous operation, particularly “extend” or “retract,” input by the operator. If the sensor  80  is inactive when a new operation is input, the control unit  100  may compare the previous operation to the new operation to determine whether to apply an acceleration or deceleration profile to the present operation. For example, if the previous operation was “retract,” and the operator stopped the reach carriage  24  when the marker  70  was within the first cushion distance C 1 , then upon receiving the new operation, the control unit  100  compares the new operation to the previous “retract” operation and: if the new operation is “extend,” the control unit  100  applies the normal acceleration profile; and, if the new operation is “retract,” the control unit  100  continues to apply the previous deceleration profile to cushion the extension arm  25  along the rest of its retraction path. 
     The sensing apparatus of  FIGS. 3-5 , which comprises the preferred embodiment of the sensing apparatus, may be considered a top-mounted sensing apparatus because the sensor  80  is disposed at or approximate to the top of the tang  60  and sensing is performed as the marker  70  moves over the top of the clevis pin  62 .  FIG. 8  illustrates a second embodiment of a sensing apparatus. The configuration of the marker  70  may remain as described with reference to  FIGS. 4 and 5 . The sensor  80  may be disposed at the top of the space between the prongs  66 ,  68  of the clevis  65 . This arrangement allows the sensor  80  to be bolted or otherwise attached to the clevis  65  without need for drilling a mounting hole. Operation of the sensor  80  otherwise proceeds as described with reference to  FIGS. 4 and 5 .  FIG. 9  illustrates another embodiment wherein the sensing apparatus senses the movement of the cylinder  55 . The illustrated embodiment may be considered a front-mounted sensing apparatus, wherein the sensor  80  is mounted to the clevis  65  forward of the tang  60 , and the marker  70  is positioned so that it is below the sensor  80  when the extension arm  25  is retracted, and rearward of the sensor  80  when the extension arm  25  is extended. Other orientations of the sensing apparatus&#39; sensor  80  and marker  70  for detecting the movement of the cylinder  55  may be used. 
     The sensing apparatus may further detect the movement of other parts of the extension arm  25  to carry out the velocity control functions described herein. Referring to  FIG. 10 , the sensor  80  may be mounted in relation to a pivot  35  where the midpoints of a first stud  125  and a second stud  130  attach. In particular, the sensor  80  may be mounted on a mount  120  attached to the first stud  125  and directed toward the pivot  35 . The marker  70  may be attached to the second stud  130  through the pivot  35  using a bearing  115 , and disposed in cooperation with the sensor  80  as described above. The bearing  115  allows the marker  70  to rotate with the second stud  130  in relation to the first stud  125 , which moves the marker  70  through the sensor&#39;s  80  range, as described above. 
     Referring to  FIG. 11 , the sensor  80  may be mounted in relation to a portion of a first stud  125 . In particular, the sensor  80  may be mounted on a mount  120  attached to the first stud  125  and directed toward the second stud  130 . In this embodiment, the second stud  130  can serve as the marker  70 . As the second stud  130  moves in relation to the first stud  125 , the sensor  80  can sense the second stud  130  as it moves through the sensor&#39;s  80  range. 
     Referring to  FIG. 12 , a switch  132 , such as a limit switch, can be coupled to a portion of the carriage frame  28 , for example. The switch can be positioned so as to sense when the reach carriage  24  is fully retracted. The switch  132  can provide a signal to the control unit  100 . Based upon the status of the signal, e.g., on or off, the control unit  100  can limit or adjust the speed of the reach truck  20  when the reach carriage is not fully retracted. 
     Preferred embodiments have been described in considerable detail. Many modifications and variations to the preferred embodiment described will be apparent to a person of ordinary skill in the art. Therefore, the invention should not be limited to the embodiments described. 
     Finally, it is expressly contemplated that any of the processes or steps described herein may be combined, eliminated, or reordered. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this invention.