Abstract:
A dock leveler, for bridging the gap between a loading dock platform and a vehicle at the dock, includes an adjustably overlapping lip and ramp that provide a traffic surface of variable length to accommodate situations where there is only a limited amount of space for the lip to rest on the rear of the vehicle. The lip pivots and translates from a stored, pendant orientation to an operative orientation with a range of extended positions. In the stored position, one edge of the lip protrudes above the deck to inhibit material handling equipment from accidentally driving over the edge of the deck when a vehicle is not parked adjacent the dock leveler.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The subject invention generally relates to dock levelers, and more specifically, to dock levelers having a lip extension. 
   2. Description of Related Art 
   Dock levelers are used to compensate for height differences between a loading dock platform and an adjacent bed of a truck or trailer. A typical dock leveler includes a deck, also known as a ramp or dockboard, which is pivotally hinged along its back edge to vary the height of its front edge. An extension plate, or lip, extends outward from the deck&#39;s front edge to span the gap between the rear of the truck bed and the front edge of the deck. The lip is usually moveable between a retracted, stored position (i.e., clear of the truck) to an extended, operative position. In the extended, operative position, the lip extends from the deck&#39;s front edge and rests upon the truck bed to form a bridge between the two. This allows personnel and material handling equipment to readily move on and off the vehicle during loading and unloading operations. 
   With some dock levelers, the lip moves linearly, as disclosed in U.S. Pat. No. 6,081,954 and German Patent DE2800128A1. The linear movement allows varying the extent to which the front edge of the lip overlaps the vehicle bed. A variable overlap can be useful when cargo rests particularly near the rear edge of the vehicle bed, and thus limits the bed&#39;s available floor space upon which the front edge of the lip may rest. In such cases, the operator may move the lip linearly up against the cargo. But this could create dangerously insufficient overlap between the lip and the truck bed; as such an approach relies on the operator&#39;s judgment. Too small of an overlap could result in loss of contact between the lip and the bed—potentially allowing the deck to fall. Another dock leveler, disclosed in German Patent DE19612135A1, has a lip fixed relative to its deck with side bumpers that move along a plane. However, all of these devices in their stored positions (also known as a cross-traffic position where an upper surface of the deck is flush with the adjacent floor) provide no significant obstruction to a forklift or other material handling equipment that might accidentally drive off the front edge of the deck when a vehicle is not present at the dock. 
   However, some dock levelers include a pivotal lip with a rear edge that protrudes above the deck when the deck is in its cross-traffic position, thereby providing an obstruction to material-handling equipment. During loading or unloading operations, a front edge of the lip pivots out over the rear edge of the truck bed, while the rear edge of the lip pivots down to overlap the deck, thus bridging the gap between the deck and the truck bed while removing the obstruction to material-handling equipment. But the extension of the lip is generally fixed, so the lip is unable to adjust to situations where there is limited floor space at the rear of a vehicle bed. 
   Another dock leveler, disclosed in U.S. Pat. No. 4,920,598, provides a pivoting lip with some sliding movement when the lip hangs generally pendant. In the stored, cross-traffic position, the sliding movement allows the lip to protrude above the deck. The protruding portion of the lip thus creates an obstruction that helps inhibit equipment from accidentally driving off the front edge of the deck. When the deck is raised from the cross-traffic position, the sliding movement allows the lip  30  to translate relative to the deck to a position where the rear or top edge of the lip no longer forms an obstruction. The lip can then be extended to a position where the rear edge of the lip abuts the front edge of the deck, thus preventing the lip from sliding back. Thus, cargo at the very back of the truck bed may interfere with a fully extended lip. So in such cases, the lip is moved to a substantially pendant position below the deck, and the deck is either moved to its cross-traffic position or to a below-dock position. In the cross-traffic position the deck is generally flush with the adjacent floor of the dock platform, and in the below-dock position, the deck is below the adjacent floor. In either case, the lip does not rest on the bed of the truck nor does it protrude above the deck. This allow some material-handling equipment, such as fork lift trucks, to drive onto the deck and reach out with their forks to place or remove loads from the very rear of the truck bed without interference from the lip. However, the gap between the deck and the truck bed (due to the lip being pendant) is generally not meant to be driven across. Thus, the gap inhibits some material handling equipment, such as pallet jacks, from loading or unloading cargo from the very rear of the vehicle bed. 
   SUMMARY OF THE INVENTION 
   In order to provide a dock leveler with a traffic surface of variable length, a dock leveler includes a lip that pivots and translates from a stored, pendant position to various operative, extended positions. 
   In some embodiments, a dock leveler includes a lip moveably coupled to a deck, such that when the deck is in a cross-traffic position, the lip protrudes above the deck to obstruct material handling equipment from accidentally driving over the edge of the deck when a vehicle is not parked adjacent the dock leveler. 
   In some embodiments a dock leveler includes a deck and a lip that together provide a traffic surface of variable length by having a variable overlap between the lip and the deck. 
   In some embodiments, a dock leveler includes deck and a lip with the lip being pivotal relative to the deck about a substantially horizontal axis and being further rotatable about a second axis generally perpendicular to the horizontal axis, whereby a forward edge of the lip can lie at various angles relative to the horizontal axis. 
   In some embodiments, a dock leveler includes a manually operated switch installed a significant distance away from a lip of the dock leveler to help encourage an operator to stay off the leveler while the lip moves from a pendant position to an extended position. 
   In some embodiments, a dock leveler includes a deck with a recess in which a lip may lie to help align an upper surface of the lip to an upper surface of the deck. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of one exemplary embodiment of a dock lever in its standby position with its lip in a stored, pendant position. 
       FIG. 2  shows the dock leveler of  FIG. 1  with its ramp having risen above the bed of a vehicle while the leveler&#39;s lip hangs in a pendant orientation relative to the ramp. 
       FIG. 3  is the same as  FIG. 2 , but with the lip pivoted outward to an intermediate orientation. 
       FIG. 4  is the dock leveler of  FIG. 1  touching its lip to a vehicle. 
       FIG. 5  shows the dock leveler of  FIG. 1  simultaneously resting a portion of the lip upon the vehicle, pivoting the ramp downward about an axis, and moving another portion of the lip toward the axis. 
       FIG. 6  shows the dock leveler of  FIG. 1  with its lip at an operative orientation and a partially extended position. 
       FIG. 7  shows the dock leveler of  FIG. 1  with its lip at an operative orientation and a fully extended position. 
       FIG. 8  is a top view of  FIG. 6  with the lip having rotated about an axis perpendicular to a horizontal axis. 
       FIG. 9  is a hydraulic schematic used in operating the dock leveler of FIG.  1 . 
       FIG. 10  is an electrical schematic associated with the hydraulic schematic of FIG.  9 . 
       FIG. 11  shows the dock leveler of  FIG. 1  with its lip pivotally fixed to force sliding motion between the lip and the deck as the deck descends. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   To compensate for height differences between a loading dock platform  10  and the bed of a vehicle  12  (e.g., truck, trailer, etc.) and to form a bridge between the two, a dock leveler  14  includes a pivotal ramp  16  with a moveable lip extension  18 , as shown in  FIGS. 1-8 . Along a rear edge  20  of ramp  16 , a hinge  22  allows ramp  16  to pivot about a generally horizontal axis  24  to adjust the height of a front edge  26  of ramp  16 . A ramp actuator  28  (e.g., fluid cylinder, diaphragm, bellows, spring, motor-driven actuator, etc.) can then move front edge  26  to the same general elevation as a rear edge  30  of vehicle  12 . 
   To bridge the gap between rear edge  30  of vehicle  12  and front edge  26  of ramp  16 , lip  18  is moveably coupled to front edge  26 . Lip  18  is interconnected to the front edge  26  to provide a variety of positions and types of motion relative to the ramp. For example, lip  18  is pivotable relative to the ramp  16  between a stored, or pendant, orientation (as in  FIG. 1 ) wherein the lip  18  is disposed generally perpendicular to ramp  16 ; and an operative orientation wherein lip  18  is pivoted so as to form a generally coplanar extension of the ramp  16 . It is in the operative orientation that lip  18  forms a bridge between the ramp  16  and the rear edge  30  of the vehicle  12 . Movement of the lip  18  to the operative orientation thus creates a traffic surface  32  ( FIGS. 6 and 7 ) extending from a front edge  34  of lip  18  to rear edge  20 , which allows personnel and material handling equipment to readily move on and off the vehicle during loading and unloading operations. 
   According to one aspect of the invention, the length of traffic surface  32  can vary. That is, with lip  18  in the operative orientation, the amount of overlap between the rear portion of the lip  18  and the front portion of the ramp  16  may be different for different operational circumstances. Indeed, the nature of the interconnection between lip  18  and ramp  16  is adapted to provide this adjustability of the length of traffic surface  32  based on the operational circumstances, as will be discussed in detail below. 
   In some embodiments, lip  18  is coupled to ramp  16  by way of a sliding connection that includes a series of studs  40  extending through a corresponding series of slots  42  in lip  18 . Studs  40  are screwed into or otherwise fastened to a hinge plate  44  of a hinge  39 . Hinge plate  44  can be one continuous plate or a series of individual plate segments, with each segment carrying one of studs  40 . A slip-fit between studs  40  and slots  42  allows the relative sliding motion, while the heads on studs  40  prevent lip  18  and hinge plate  44  from separating. Hinge  39 , in turn, pivotally couples plate  44  to ramp  16  to provide lip  18  with pivotal motion about a substantially horizontal axis  48  for certain operational circumstances, and to provide lip  18  with a fixed reference point for a more complex translating/rotational motion for other operational circumstances, as discussed below. 
   When the lip  18  is in the pendant orientation of  FIGS. 1 and 2 , the sliding connection allows the lip  18  to slide relative to the ramp  16  between a stored, pendant position (in which the lip  18  extends above the ramp  16  to form an obstruction to material handling equipment that might otherwise accidentally drive of the front edge of the ramp  16 ) as in  FIG. 1 , and a retracted, pendant position in which the rear edge of the lip  18  does not extend above the upper surface of the ramp  16 , as in FIG.  2 . According to the embodiment, movement of lip  16  from the stored, pendant position to the retracted, pendant position is caused by relative movement between the ramp  16  and lip  18 . That is, lip  18  remains substantially fixed as ramp  16  is raised to the  FIG. 2  position. The sliding connection between the lip  18  and ramp  16  facilitates this movement. In this regard, the sliding connection between lip  18  and ramp  16  is similar to the one disclosed in U.S. Pat. No. 4,920,598, which is specifically incorporated by reference herein. 
   In distinction to the &#39;598 patent, however, the sliding connection according to this embodiment also provides for a sliding translation of the lip  18  relative to the ramp  16  for the full range of lip orientations between the pendant orientation and the operative orientation. For example, in the operative orientation according to this embodiment, rotation of the lip about axis  54  allows lip  18  to adjust to situations where vehicle  12  and/or load  36  are disposed at a slight angle to dock face  10 , as shown in FIG.  8 . Such movement does not appear to be possible in the context of the &#39;598 patent as the rear edge of the lip abuts a vertical surface on the ramp when the lip is in the operative orientation ( FIG. 3  of &#39;598). Perhaps more importantly, the interconnection between the lip  18  and ramp  16  in this embodiment is also distinct from that shown in the &#39;598 patent, as the interconnection here provides for sliding movement of the lip relative to the ramp  16  at intermediate orientations between the pendant and operative orientations. It is this movement that allows the amount of overlap between the rear portion of lip  18  and the front portion of deck  16  to be different for varying operational circumstances, and thus to adjust the length of the traffic surface  32  depending on those circumstances. To provide this enhanced functionality relative to the &#39;598 patent, the position of slots  42  in lip  18  and the height of hinge  39  relative to traffic surface  32  are different to allow lip  18  to slide relative to ramp  16  throughout the range of lip orientations. More specifically, slots  42  are shifted further away from a rear edge  62  of lip  18  and hinge  39  is raised to be closer to traffic surface  32 . 
   The operational advantages provided by this structure will now be discussed in greater detail, particularly in regard to the ability of the length traffic surface  32  to be adjusted depending on operational circumstances. In one operational circumstance, the vehicle being unloaded has ample floor space at the rear to receive the lip  18 . In this instance, the leveler according to this embodiment would be operated conventionally. Ramp  16  would be raised until studs  40  engaged the tops of slots  42  and raised lip  18  out of lip keepers  60 . Once the front edge of lip were high enough for front edge  34  to clear the bed of the vehicle, the lip would be rotated fully to the operative orientation. To pivot lip  18  about axis  48 , a lip actuator  50  (e.g., fluid cylinder, diaphragm, bellows, spring, motor-driven actuator, etc.) is coupled to a lug  52  that rigidly extends from hinge plate  44 . As actuator  50  extends, lip  18  pivots outward. When the lip is fully rotated to the operative orientation, the ramp  16  and now generally co-planar lip  18  can be lowered onto the bed of vehicle  12 , to facilitate the unloading or loading process. In this circumstance, the length  38  of traffic surface  32  is at its maximum, as the lip in the operative orientation has its most minimal overlap with ramp  16  (see FIG.  7 ). That is, lip  18  is in an extended position in its operative orientation. 
   A hydraulic circuit  64  of FIG.  9  and an electrical circuit  66  of  FIG. 10  can control the operation of dock leveler  14 . A typical operating sequence would begin with dock leveler  14  in its standby position of FIG.  1 . In this position, ramp  16  is in its cross-traffic position where an upper surface  58  of ramp  16  is generally flush with the adjacent floor of dock  10 . Lip  18  is stored in a generally pendant orientation with front edge  34  of lip  18  supported by lip keepers  60  and with a rear edge  62  of lip  18  protruding above upper surface  58  of ramp  16 . Edge  62  protruding above surface  58  creates an obstruction to material handling equipment that might otherwise accidentally drive over the front edge  26  of ramp  16  when vehicle  12  is not present at dock  10 . With dock leveler  14  in its standby position, the operating states of the components of circuits  64  and  66  are as shown in  FIGS. 9 and 10 . 
   Once vehicle  12  backs up against a set of bumpers  68  of dock  10 , a pump switch  70  can be actuated to raise ramp  16 , as shown in FIG.  2 . Pump switch  70  includes two normally opened contacts  72  and  74 . With supply voltage across lines  76  and  78 , contacts  72  energize a motor relay coil  80  of a conventional motor starter (not shown) that starts a motor-driven hydraulic pump  82 . Pump  82  draws hydraulic fluid from a tank  84  and through a filter  86  to deliver pressurized fluid to a hydraulic fluid line  88 . A set of contacts  94  of a limit switch  96  and one set of normally closed contacts  98  of a lip switch  100  energizes a solenoid  90 , which maintains the open position of a solenoid valve  92  (e.g., a two-way, two-position, solenoid-actuated, spring return valve). Contacts  94  of limit switch  96  are normally open but held closed by a first cam  102  when lip  18  is in the pendant orientation relative to ramp  16 , as shown in  FIGS. 1 and 2 . With pump  82  running, hydraulic fluid in line  88  pressurizes a pilot line  106  to shift a shuttle valve  104  (e.g., a three-way, two-position, pilot-operated, spring-return valve) from its normal position of FIG.  9 . Pressurized hydraulic fluid then passes in series through line  88 , passage  108  of valve  104 , a line  110 , open solenoid valve  92 , a line  112 , and velocity fuse  114  and into actuator  28 , which raises ramp  16 . Velocity fuse  114  simply controls the reverse flow from ramp actuator  28  to stop movement of ramp  16  in the event of an unexpected adverse operating condition. 
   After ramp  16  rises high enough for front edge  34  of lip  18  to clear the bed of vehicle  12 , as shown in  FIG. 2 , an operator can extend lip  18  by actuating lip switch  100  while maintaining contacts  72  and  74  of pump switch  70  closed. Lip switch  100  being actuated opens contacts  98  and  116  to de-energize solenoid  90 , which closes solenoid valve  92 . With solenoid valve  92  closed, pressure builds in line  110  and a pilot line  118  to shift a sequence valve  120  (e.g., a three-way, two-position, pilot-operated, spring-return valve) that is set to shift at a predetermined pressure greater than that which is necessary to lift ramp  16 . Sequence valve  120  shifting from its normal position of  FIG. 9  delivers pressurized fluid from line  110 , through a line  122 , through a normally open solenoid valve  123 , and to lip actuator  50 , which starts pivoting lip  18  outward. 
   Lip  18  can be pivoted fully to the operative orientation if load  36  leaves sufficient floor space at the rear of vehicle  12 , as shown in FIG.  7 . When vehicle  12  has no load obstructing the full extension of lip  18 , dock leveler  14  can be operated in a conventional manner similar to other dock levelers that fully extend their lip. However, if load  36  leaves limited floor space at the rear of vehicle  12 , lip  18  can be partially pivoted relative to ramp  16  to an intermediate orientation to just reach over what space is available, as shown in FIG.  3 . With lip  18  in a partially pivoted orientation, cam  102  releases switch  96  to close solenoid  90 . This creates a condition at which ramp  16  can be lowered to set the partially pivoted lip down on top of the vehicle bed. 
   To lower ramp  16  from its position of  FIG. 3  to that of  FIG. 4 , pump switch  70  is released to open contacts  72  and  74 , while a ramp descent switch  124  is actuated. Actuating switch  124  closes its normally open contacts  126  to energize solenoid  90  and thus open valve  92 . With pump  82  turned off and solenoid valve  92  open, the weight of ramp  16  pushing against ramp actuator  28  forces hydraulic fluid to drain from actuator  28  to tank  84 . Due to an adjustable flow restriction  128  in shuttle valve  104 , ramp  16  descends at a controlled rate, as hydraulic fluid flows in series through velocity fuse  114 , line  112 , open solenoid valve  92 , and flow restriction  128 . Ramp descent switch  124  is preferably of a spring-return style where switch  124  needs to be manually attended to keep its contacts  126  closed. This helps ensure that an operator is unable to obstruct the movement of lip  18  with any portion of his body, provided switch  124  is remotely located relative to lip  18 . In other words, the operator would have to make an intentional effort to hold the switch down and simultaneously obstruct the movement of lip  18 . Otherwise, when tip  34  is against vehicle  12 , an operator might inadvertently obstruct the downward rotation of rear edge  62  as ramp  16  descends. 
   To compensate for limited available floor space caused by load  36  being particularly near the rear of vehicle  12 , rear edge  62  of lip  18  moves back relative to ramp  16 , as ramp  16  descends from its position of  FIG. 4  to that of FIG.  5 . To do this, load  36 , being an obstruction to further extension of lip  18 , forces rear edge  62  of lip  18  to overlap ramp  16  as ramp  16  descends. Varying the amount of overlap adjusts length  38  of traffic surface  32  or the distance between axis  24  and the rear of load  36 . In some embodiments, the movement between lip  18  and ramp  16  is, in part, a sliding motion guided by studs  40  sliding within slots  42 . While rear edge  62  of lip  18  moves toward axis  24 , lip  18  continues rotational movement. 
   Once lip  18  moves upward (relative to ramp  16 ) beyond its position shown in FIG.  5  and into the operative orientation of  FIG. 6  (either by powered movement or because of deck descent), ramp descent switch  124  can be released. To sense the pivoted positions of lip  18 , an arm  130  carrying cams  102 ,  132  and  134  has one end fixed to a rod end  136  of lip actuator  50  while an elongated portion of arm  130  slides within a guide  138  fixed relative to the cylinder of actuator  50 . As rod end  136  extends and retracts, arm  130  moves cams  102  and  132  across limit switch  96  and moves cam  134  across a roller arm actuator  142  of a limit switch  140 . As lip  18  moves from its position of  FIG. 5  to that of  FIG. 6 , cam  132  actuates limit switch  96 . Cam  132  closing limit switch  96  keeps solenoid valve  92  open (regardless of switch  124 ) by energizing solenoid  90  through the closed contacts  94  of limit switch  96  and the normally closed contacts  98  of lip switch  100 . With cam  132  holding the contacts of limit switch  96  closed, solenoid valve  92  remains open while dock leveler  14  is in the position shown in FIG.  6 . Solenoid valve  92  being open allows ramp  16  to “float” with the incidental up and down movement of vehicle  12 , as vehicle  12  is being loaded or unloaded of its cargo. 
   To minimize any impedance to material handling equipment traveling between lip  18  and ramp  16 , in some embodiments, ramp  16  includes a pocket or recess  144  into which lip  18  lies when in the operative orientation. In other embodiments; however, lip  18  simply overlays surface  58  of ramp  16  without a recess. 
   After completing the loading or unloading of vehicle  12  and vehicle  12  departs the dock area, ramp  16  descends under its own weight, as cam  132  actuating limit switch  96  keeps solenoid valve  92  open. Once ramp  16  bottoms out (e.g., ramp  16  abuts some mechanical stop), the pressure in line  112  drops virtually to zero, as actuator  28  no longer supports the weight of ramp  16 . The absence of significant pressure in line  112  allows the hydraulic fluid in line  122  (which is pressurized by the weight of lip  18  pushing against lip actuator  50 ) to release through a pressure relief valve  146 , thereby pivoting lip  18  downward by the weight of lip  18  and/or by a biasing force of compression spring  125  in cylinder  50 . Although slight downward movement of lip  18  causes cam  132  to release limit switch  96 , cam  134  trips limit switch  140  just before cam  132  disengages limit switch  96 . Cam  134  closing the contacts of limit switch  140  restarts pump  82  and keeps solenoid valve  92  open. Thus, ramp  16  begins rising due to pressurized hydraulic fluid entering ramp actuator  28  upon flowing in series through fluid line  88 , line  110 , solenoid valve  92 , line  112  and velocity fuse  114 . 
   Meanwhile, lip  18  continues pivoting downward by way of hydraulic fluid draining from lip actuator  50  to tank  84  upon flowing in series through normally open valve  123 , line  122 , a pilot-operated check valve  150  (held open by a pilot line  152  being pressurized by line  88 ), and a flow restrictor  154 . The upward movement of ramp  16  and the relative downward movement of lip  18  continue until lip  18  achieves the pendant orientation. 
   At that point, cam  134  releases limit switch  140  just after cam  102  trips limit switch  96 . This turns pump  82  off as the contacts of limit switch  140  and pump switch  70  are open. Yet, cam  102  tripping limit switch  96  continues to energize solenoid  90  of valve  92  through closed contacts  98  of lip switch  100  and the closed contacts  94  of limit switch  96 . Thus, ramp  16  descends to its standby position of  FIG. 1 , as hydraulic fluid escapes from ramp actuator  28  by flowing in series through velocity fuse  114 , line  112 , open solenoid valve  92 , and flow restriction  128  of shuttle valve  104 . 
   When wanting to place the last load on the end of vehicle  12 , lip  18  may need to be slid back without the aid of a load already in place to help push lip  18  back. To do this, ramp  16  and lip  18  are first moved to the position of FIG.  3 . From there, dock leveler  14  can be lowered to the position of  FIG. 11  by actuating ramp descent switch  124  and a lip-lock switch  127  at the same time. Lip-lock switch  127  energizes a solenoid  129  to close valve  123 , which helps prevent lip  18  from pivoting in either direction. Thus, as ramp  16  descends due to switch  124  opening solenoid valve  92 , lip  18  is forced to slide back as front edge  34  abuts vehicle  12 . Once lip  18  is slid back, liplock switch  127  can be released, so that further downward movement of ramp  16  can force rear edge  62  of lip  18  to pivot downward until dock leveler  14  is in the position of  FIG. 6  (but without load  36  already in place). 
   Although the invention is described with respect to a preferred embodiment, modifications thereto will be apparent to those skilled in the art. For example, a pressure relief valve  156 , as shown in  FIG. 9 , can be added to line  110  to limit the maximum pressure in the hydraulic system. Therefore, the scope of the invention is to be determined by reference to the claims that follow.