BACKGROUND ART A typical walkie/rider pallet truck includes load carrying forks and a power unit having a steerable wheel, a steering control mechanism, a brake including a deadman brake mechanism, an electric traction motor, a storage battery and a platform onto which the operator may step and ride while controlling the truck. The steering mechanism normally has a handle mounted at the end of a movable steering arm with the handle including controls for raising and lowering the forks and rotatable twist grips or comparable devices to control the speed and direction (forward and reverse) of the truck. A switch for reversing vehicle travel direction when traveling in the power unit first or forward direction and a horn switch are also normally provided on the handle.

In stock picking operations, a truck operator typically follows a winding, unidirectional route through the warehouse, picking up stock in a predetermined sequence in order to maximize productivity. The operator normally walks alongside the truck when the distance along the route between picks is short and steps onto the truck platform to ride when the distance between picks is longer, for example twenty or more feet. When the operator is riding on the truck platform, it is desirable for optimum work productivity to move the truck at higher speeds than when the operator is walking beside it. To this end, speed controllers that include high and low speed control circuits are provided.

For movement of the truck, the operator grasps the handle and moves the steering arm into a truck operating range between a generally vertical (up) braking position and a generally horizontal (down) braking position. If the operator releases

the handle, the deadman brake mechanism, for example comprising an arm return spring, forces the arm to the up braking position which actuates a spring-loaded brake to stop the truck. The operator can also actuate the spring-loaded brake by bringing the steering arm to the down braking position. Thus, the walkie/rider pallet truck may be in either a braking or non-braking mode, depending on the position of the steering arm within specified braking and operating arcs.

Rotation of the twist grips controls movement of the truck: rotation of either grip in one direction causes the truck to move with the power unit leading, the forward direction, while rotation in the opposite direction causes the truck to move with the load carrying forks leading, the backward or reverse direction. Increased rotation of the grip in either direction, when operated in either the walkie or the rider mode, results in an increase in the power supplied to the electric motor causing the truck to move at a higher speed in the corresponding forward or reverse direction.

In addition to the motion control provided by the rotatable twist grips, rider pallet trucks may also include side or"jog"switches. The jog switches can be turned on and off by an operator walking alongside the truck to move the vehicle at a walk speed of around 3.5 miles per hour (mph) (5.6 km/hr) to move from one stock pick position toward the next stock pick position. A single jog switch is normally provided on each side of the handle either on an outer portion of the handle or, preferably, on an inner, protected portion of the handle. An example of another jog switch arrangement, wherein a pair of switches, one on the outside of the handle and one on the inside of the handle, is provided on each side of the handle and both switches must be activated to move the truck, is illustrated in U. S.

Patent No. 5,245,144 which is entitled WALK ALONG HAND GRIP SWITCH CONTROL FOR PALLET TRUCK which issued on September 14,1995 to the assignee of the present application and is incorporated herein by reference.

The efficiency of stock picking is severely hampered if the brake is activated every time an operator releases the steering arm. Thus, brake override, or coasting, systems have been developed to override the deadman brake mechanism by preventing the steering arm from entering the up braking position when the

operator releases the handle/steering arm while walking alongside the truck. When operating in the coast mode, arrangements are provided for a walking operator to apply the service brake and sound the horn.

One such system for deactivating a deadman brake is disclosed in U. S.

Patent No. 3,791,474 which is entitled MOTION SELECTOR DEVICE FOR A LIFT TRUCK and issued on February 12,1974 to Crown Controls Corporation, a predecessor in interest to the assignee of the present application. In the'474 patent, a spring device is manually pivoted into a position for engaging the steering arm and preventing the arm from entering a vertical braking arc under the force of a deadman spring.

Another system for deactivating a deadman brake is disclosed in U. S. Patent No. 4,716,980 which is entitled CONTROL SYSTEM FOR RIDER VEHICLES and issued on January 5,1988. In the'980 patent, a selector switch is used to select either normal high speed operation or coasting operation and additional switches are then used to drive a truck within the high speed range or in the coast mode.

Thus, the coasting system of the'980 patent requires manual engagement of the deadman brake override control device by the vehicle operator to put the truck in its coast mode or to disengage the coast mode for high speed travel.

Another system for automatic engagement and disengagement of a deadman brake is disclosed in U. S. Patent No. 5,964,313 which is entitled MOTION CONTROL SYSTEM FOR MATERIALS HANDLING VEHICLE and issued on October 12,1999. In the'313 patent, a coast control device can only be engaged by activation of a jog button that actuates a low speed travel mode. The coast control device is deactivated by activation of a maximum speed control button or movement of speed control hand grips from their neutral position. The coast control device comprises a coast control spring that is compressed by a solenoid to apply a coast spring force that compensates the force provided by a handle return spring to constrain the steering arm to a driving arc. While the automatic engagement and disengagement of coast control improves on operation of the truck during stock picking, the disclosed coast control mechanism is mechanically complicated and,

when engaged and the handle is released, forces the handle into a single detent- defined position within the driving arc. Further, since the coast control device can only be engaged by activation of the jog button, the'313 coast control cannot be used on vehicles that do not have the jog feature.

Accordingly, there is a need for a mechanically less complicated coast control arrangement for walkie/rider pallet trucks that would have less parts, be easier to assemble and maintain, and enable an operator to retain the handle at any position within the operating arc, allow the coast system to be overridden for applying the brake, allow coast to be used on walkie/rider pallet trucks that do not have the jog feature, limit truck speed to approximately 3.5 mph (5.6 km/hr) when the coast mode is selected, and provide improved operation of the truck for stock picking.

DISCLOSURE OF INVENTION This need is met by the invention of the present application wherein a device locks the position of a steering arm of a walkie/rider pallet truck to prevent movement of the steering arm by a deadman mechanism that would otherwise move the steering arm into a generally vertical truck braking position. By locking the position of the steering arm to overcome the deadman mechanism, the truck is placed into a coast mode of operation. The currently preferred locking device is a steering arm brake comprising an armature plate mounted to and movable with the steering arm and an electromagnet coupled to a steering head to which the steering arm is movably mounted so that the armature plate moves over the electromagnet.

The coast mode of truck operation is activated by operating the electromagnet to attract the armature plate and thereby lock the steering arm into the position it occupies when the coast mode is activated. While the braking force locks the steering arm and prevents movement of the steering arm by the deadman mechanism, the force can be overcome by the truck operator to manually apply the truck brake or to reposition the steering arm to a new position where it is again locked until it is once again moved to a new position, the truck is braked or the coast mode is released.

The invention of the present application also provides novel control for coasting operation of a walkie/rider pallet truck. A coast control mechanism for overriding a deadman brake to enable coasting operation of a walkie/rider pallet truck is manually engaged by an actuator or coast switch that is mounted on or closely adjacent to a grab bar that is provided on the truck and is to be gripped by an operator riding on the truck. The actuator can be on the grab bar, on a control panel mounted on the grab bar or mounted to be easily accessible by an operator's hand gripping the grab bar for operation of the truck and coast actuation. Coasting operation of the truck is cancelled by manually operating a high speed/coast release switch.

Additional features and advantages of the invention will be apparent from the following description, the appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a perspective view of a walkie/rider pallet truck of the type into which the present invention is incorporated; Figs. 1A and 1 B are perspective front and rear views, respectively, of a control panel mounted on a grab bar of the truck of Fig. 1; Fig. 2 is a perspective view of a control handle of the truck of Fig. 1; Fig. 3 is a perspective view of a portion of a steering control unit of the truck of Fig. 1 showing the pivoting movement of a steering arm of the truck and a brake deadman mechanism; Fig. 4 is a partially broken away side view a portion of the steering control unit of the truck of Fig. 1 showing a steering arm locking device of the present invention;

Fig. 4A is a partially sectioned side view showing resilient biasing of an electromagnet of a steering arm brake into an armature plate of the brake; Fig. 4B is a partially sectional view of the steering arm brake taken along the section line 4B-4B of Fig. 4; Fig. 5 is a side view of a portion of the truck of Fig. 1 showing the pivoting motion of a steering arm/handle combination of the truck; Figs. 6 and 7 illustrate a steered wheel brake in the operated and non- operated positions, respectively, Fig. 8 is a schematic block diagram of a portion of the control system for the truck of Fig. 1; and Figs. 9 and 10 are state diagrams used by the controller of Fig. 8 to operate the truck of Fig. 1 in accordance with one aspect of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Reference will now be made to the drawings for description of the coast control mechanism and control of the present application. In the drawings, Fig. 1 illustrates a walkie/rider pallet truck (100) including and operable in accordance with the present invention. The truck (100) includes a power unit (102), a steering control unit (104), and load carrying forks (106) that extend rearwardly from the power unit (102). The power unit (102) contains a steerable wheel (not shown), usually located directly beneath the steering control unit (104), an electric traction motor (not shown), and an electric storage battery (108). The power unit (102) also includes a platform (110) onto which an operator may step and ride while controlling the truck (100). A hand rail or grab bar (112) is provided for an operator to grip while riding on the platform (110). A control panel (115) is mounted on the grab bar (112) and includes a high speed/coast release switch (HS/CR) (115A), a horn

switch (115B), a raise forks switch (115C), a lower forks switch (115D) and a coast switch (CS) (115E). See Figs. 1A and 1 B.

The steering control unit (104) includes a handle (114) mounted at the distal end of a steering arm (116) that is pivotally mounted to the steering control unit (104) as will be described more fully with reference to Fig. 3. The operator uses the handle (114) to control steering, braking and other truck functions. To this end, the handle (114) includes operator controls, such as twist grips (118) for controlling the direction (forward and reverse) and speed of the truck (100), a reverser switch (120), switches (122) and (124) for raising and lowering the forks (106), respectively, and a horn switch (126), see Fig. 2.

The steering arm (116) is moved from side to side to rotate the steering control unit (104) relative to the power unit (102) to determine the steered direction of the truck (100). The steering arm (116) is also used to apply a brake (117) to stop the steerable wheel, see Figs. 6 and 7 where the steerable wheel brake (117) is shown operated and released, respectively. It will be apparent to those skilled in the art that the steerable wheel brake (117) can be constructed to directly brake the steerable wheel ; to brake the traction motor driving the steerable wheel and thereby indirectly brake the steerable wheel ; or, to be coupled to a transmission interconnecting the traction motor and the steerable wheel to directly brake the transmission and thereby indirectly brake the steerable wheel. All of these and any other arrangements for braking the steerable wheel will be generically referred to herein as a steerable wheel brake.

For braking the truck (100), the steering arm (116) is moved to either a generally horizontal (down) braking position within a horizontal braking arc (119) or a generally vertical (up) braking position within a vertical braking arc (121), see Fig.

5. For movement of the truck (100), the steering arm (116) is moved to a traveling, operating or driving position within a driving range or arc (123) interposed between the horizontal and vertical braking arcs (119), (121), see Fig. 5. When traveling in the power unit first or forward direction, the truck (100) will be reversed if the reverser switch (120), located at the forward part of the handle (114), is activated.

The twist grips (118) are spring biased to a center neutral position. Rotating either of the grips (118) forward will cause the truck (100) to move forward at a speed proportional to the amount of rotation of the grips (118). Similarly, rotating either of the grips (118) toward the rear of the truck (100) will cause the truck (100) to move in reverse again at a speed proportional to the amount of rotation of the grips (118).

As an optional feature on walkie/rider trucks, switches that can be operated from the side of the trucks, referred to as"jog"switches, can also be provided to move or jog the trucks in the forward direction at a predetermined low speed. Jog switches (128) can be located on the outsides of the ends of the handle (114); or, jog switches (130) can be located on the insides of the ends of the handle (114). It is apparent that the jog switches (130) are better sheltered from inadvertent activation since they are protected by the handle (114) and thus are preferred. In any event, an operator walking beside a truck can move the truck by operating the jog switches. While either the jog switches (128) or the jog switches (130) are provided on many walkie/rider pallet trucks equipped with jog switches, an improved jog arrangement including both jog switches (128), (130) on each side of the handle (114) as disclosed in U. S. Patent No. 5,245,144 provides still better protection against inadvertent activation and is illustrated in the present application. For additional information regarding the improved jog switch arrangement, reference should be made to the'144 patent.

When the steering arm (116) is moved into the horizontal braking arc (119) or the vertical braking arc (121), a switch (131) cuts power to the electric traction motor and actuates the steerable wheel brake (117) to stop the truck (100), see Figs. 6 and 7. The vehicle brake can, thus, be engaged manually by the operator forcing the arm (116) to a braking position (the up braking position or the down braking position) or, if the operator releases the arm (116), by operation of a brake deadman mechanism (133) that automatically drives the arm (116) into its up braking position. The deadman mechanism (133) is illustrated as that provided on Walkie/Rider Pallet Trucks commercially available from the Crown Equipment Corporation, assignee of the present application, and comprises three torsion springs (133A), (133B) and (133C) which are coupled between a steering head

(132) and the steering arm (116) as shown in Fig. 3. Three torsion springs are provided to facilitate production of the springs and so that a variety of spring forces can be easily selected for varying weight steering arm/handle combinations by selection of the torsion springs. Operation of the deadman mechanism (133) may be prevented by a deadman override device that allows the vehicle to operate in a coast mode.

Overriding the deadman mechanism (133) for coast operation of walkie/rider pallet trucks in accordance with one aspect of the present invention will now be described with reference to Figs. 3 and 4 which illustrate a relevant portion of the steering control unit (104) of the truck (100) of Fig. 1. The steering arm (116) is mounted to a steering head (132) for pivotal movement about an axis A and is spring biased into a generally vertical braking position within the vertical braking arc (121), i. e., the up braking position, by a torsion spring force generated by the torsion springs (133A-133C) that form the brake deadman mechanism (133) for the illustrated embodiment. Thus, when the handle (114) is released by an operator, the springs (133A-133C) raise the steering arm (116) to brake the truck (100). Of course, other brake deadman mechanisms can be used in the present invention, for example, the deadman mechanism disclosed in U. S. Patent No. 5,964,313.

In accordance with the present invention, to provide coast control for the truck (100), a locking device (136) locks the steering arm (116) into any selected position, at least within the driving arc (123), so that the brake deadman mechanism (133) is overridden and prevented from moving the steering arm (116) into its generally vertical, up braking position. While the locking device (136) applies a locking force to the steering arm (116) that overcomes the brake deadman mechanism (133) to fix the steering arm's (116) position, the locking force is selected such that it can be overcome by the operator of the truck (100) for moving the steering arm (116) to manually apply the steerable wheel brake (117) and also for moving the steering arm (116) to other selected locations where the locking device (136) will again retain the steering arm (116). In a working embodiment of the invention, the locking device (136) comprises a steering arm brake as illustrated in the present application. Of course, review of the present disclosure will suggest

a number of locking devices that can be used in the present invention, for example, detented or segmented locks wherein a tab can be selectively engaged into one of a plurality of opposing detents to define a corresponding number of locked positions as well as a variety of steering arm brake arrangements in addition to that illustrated in the present application.

When the illustrated steering arm brake is used as the locking device (136), it advantageously provides a virtually limitless number of positions within the vertical movement range of the steering arm (116) into which the steering arm (116) can be locked as opposed to a defined number of positions for a locking device relying on detents or segments that define discrete locking positions. In the illustrated embodiment of Figs. 3 and 4, the steering arm brake comprises an armature plate (138) and an electromagnet (140) with the brake being engaged by activation of the electromagnet (140) to attract the armature plate (138).

The armature plate (138) is connected to the steering arm (116) and is moved through an arc (139) as the steering arm (116) is moved between its down braking position and its up braking position. In Fig. 4, the armature plate (138) is shown in solid lines when the steering arm (116) is in its down braking position, is shown in dotted lines when the steering arm (116) is in its up braking position and can be positioned anyway between these two extremes as the steering arm (116) is moved between its down braking position and its up braking position. In a working embodiment, the armature plate (138) was made from low carbon steel, such as grades 1008 through 1035, and nickel plated to a thickness of between 0.0007 and 0.0010 of an inch to prevent corrosion and give a smooth surface that reduces noise as the armature plate (138) slides over the electromagnet (140). It is noted that other materials and material finishes can be used for the armature plate (138) of present invention as will be apparent to those skilled in the art.

The electromagnet (140) includes a solid body (140A) having an annular groove (140B) formed in its forward surface [the surface facing the armature plate (138)] for receiving an electrical coil (140C) which is electrified to activate the electromagnet (140), see Figs. 4,4A and 4B. The electromagnet (140) is supported

on a plate 132A connected to the front portion of the steering head (132). A socket head cap screw (140D) engages a threaded aperture (132B) in the plate (132A) to secure a mounting pin (140F) to the plate (132A). A bushing (140E) is pressed into the solid body (140A) of the electromagnet (140) with the mounting pin (140F) sized to be received within the bushing (140E). In the illustrated embodiment, the electromagnet (140) is mounted for axial movement relative to the plate (132A) and is spring biased away from the plate (132A) and into engagement with the armature plate (138) by means of a compression spring (140G).

The compression spring (140G) surrounds the mounting pin (140F), extends between the solid body (140A) and the plate (132A), and, in a working embodiment, provided a force of about 1/2 pound, see Figs 4A and 4B. By spring biasing the electromagnet (140) into the armature plate (138), the distance between the two is maintained to accommodate tolerance build up in the pivotal mounting of the steering arm (116) to the steering head (132) and to ensure consistent magnetic forces when the brake is applied. The body (140A) of the electromagnet (140) is prevented from rotating about its axis by a notch (140H) in the body (140A) which receives a pin (132C) extending from the plate (132A). In the illustrated embodiment, the solid body (140A) is retained on the mounting pin (140F) against the force of the compression spring (140G) by its engagement with the armature plate (138).

In a working embodiment, the body (140A) of the electromagnet (140) was made from cold finished steel that has a Salt Bath Nitriding (SBN) finish produced by a ferritic nitrocarburising process that adds both nitrogen and carbon to the ferrous surface of the body (140A). The nitrogen and carbon atoms form a compound layer in the surface and a deep diffusion zone beneath the layer that ranges between approximately 0.0002 and 0.0008 of an inch and that has a hardness of approximately Rockwell C 58 to 60. The surface layer increases corrosion protection, provides lubricating properties for the body and resists abrasive wear between sliding surfaces. The surface layer is also nonmagnetic and provides a nonmagnetic gap, functionally similar to an air gap, between the electromagnet (140) and the armature plate (138) to prevent sticking due to residual

magnetism. It is noted that other body materials and material finishes can be used in the present invention as will be apparent to those skilled in the art.

A changing portion of an inner surface (138A) of the armature plate (138) is positioned against the electromagnet (140) as the armature plate (138) moves through the arc (139) as the steering arm (116) is moved through the horizontal braking arc (119), the driving arc (123) and the vertical braking arc (121). As shown in Fig. 4, a portion of the armature plate (138) is always against the electromagnet (140) throughout the travel range of the armature plate (138) even though the surface area of the armature plate (138) contacting the electromagnet (140) is reduced to minimums at the ends of the travel range of the armature plate (138) and the steering arm (116).

During movement of the steering arm (116) within the driving arc (123), the electromagnet (140) is substantially fully covered by corresponding portions of the armature plate (138). Thus, the braking force exerted by activation of the electromagnet (140) is assured to lock the steering arm (116) in the position within the driving arc (123) that the steering arm (116) occupies when the electromagnet (140) is activated or in a subsequent position within the driving arc (123) to which the steering arm (116) is moved while the electromagnet (140) is activated. Locking within the horizontal braking arc (119) and the vertical braking arc (121) is not assured; however, locking at any position within the vertical range of motion of the steering arm (116) can be assured by enlargement of the armature plate (138) so that the electromagnet (140) is fully covered at all positions of the armature plate (138) within its travel range, i. e., the arc (139).

As noted above, the braking force is selected so that the steering arm (116) is fixed and not moved by the brake deadman mechanism (133). However, the force can be overcome by an operator to manually apply the steerable wheel brake (117) or to reposition the steering arm (116). To move the steering arm (116), an operator must apply a force greater than the difference between the restraining force or torque generated by the electromagnet (140) and the force or torque applied by the deadman mechanism (133), i. e., the springs (133A-133C). It is

currently believed that if the required operator force is set to a value which prevents movement of the steering arm (116) in response to the truck (100) going over bumps of a common size in the floor that it will be acceptable to all operators of the truck. This force can be increased or reduced for given applications and to accommodate given operators as long as the force is adequate to ensure proper coasting operation of the truck (100). In a working embodiment of the present invention, the proper forces/torques were obtained by using an electromagnet that generated an attractive force of approximately seventy (70) pounds.

It is apparent that the locking device of the present invention provides a coast control for walkie/rider pallet trucks that is mechanically less complicated than many prior art devices and has less parts so that it is easier to assemble and maintain. Further, the locking device enables an operator to position the handle/steering arm at any location within the driving arc and retains the handle/steering arm in that position unless the locking device/coast system is overridden for manually applying the vehicle brake or to reposition the handle/steering arm to a different desired position where it will again be retained.

In addition to the novel deadman brake override system described above, another aspect of the present invention is the control of the system (or any other deadman brake override or coast control system). In the illustrated embodiment of the present invention, control for overriding a deadman brake is incorporated into a controller (142) of the truck (100). See Fig. 8 which is a schematic block diagram of a portion of the control system for the truck (100) wherein normally open contacts are indicated by an"X"and normally closed contacts are indicated by a"I". In a working embodiment of the present invention, the controller (142) is a Sevcon Millipak controller for separately excited motors (SEM) that includes microprocessor control, however, a variety of other controllers can be used in the present invention.

Inputs to the controller (142) include the high speed/coast release switch (115A), the coast switch (115E) and the twist grips (118). Movement of the truck (100) is enabled by a brake switch (144) which is connected to the reverser switch (120). If the reverser switch (120) is not activated, reverse switch (146) and forward switch (148) are enabled so that the direction of travel of the truck (100) is determined by

which of the switches (146) and (148) is activated. If the reverser switch (120) is activated, the switches (146) and (148) are disabled and a signal to reverse the truck (100) is sent to the controller (142).

Figs. 9 and 10 illustrate state diagrams which are used by the controller (142) to operate the truck (100) in accordance with the present invention. In Fig. 9, high speed operation of the truck (100) is enabled by continuous activation of the high speed/coast release switch (115A), i. e., the operator must hold the high speed/coast release switch (115A) in its operated position. In Fig. 10, high speed operation of the truck (100) is enabled by momentary activation of the high speed/coast release switch (115A) while a speed command is provided, i. e., while the operator maintains either of the twist grips (118) out of their neutral positions.

Each of the state diagrams include the same three states: a low speed state (150); a high speed state (152); and, a coast state (154). In the low speed state (150), the speed of the truck (100) is limited to a low speed, for example a walk speed of approximately 3.5 miles per hour (mph) [5.6 kilometers per hour (km/hr)]. In the high speed state (152), the truck (100) can be operated: at speeds up to an intermediate speed, greater than the low speed, in the forks first or reverse direction; and, at speeds up to a high speed, greater than the intermediate speed, in the power unit (102) first or forward direction. In the coast state (154), the speed of the truck (100) is limited to a low speed that normally would be the same as the limited low speed of the low speed state (150).

The controller (142) enters the low speed state (150) at key on of the truck (100), i. e., when the truck key is moved from off to on, so that the truck (100) can then be operated at the limited low speed by operation of the twist grips (118) and/or the jog controls, such at the jog switches (128) or (130) [or both the jog switches (128) and (130)], if provided. The high speed state (152) can be entered from the low speed state (150) by activating either of the twist grips (118) to generate a speed command [other than zero provided at the neutral position of the twist grips (118)] and activation of the high speed/coast release switch (115A). For operation in accordance with the state diagram of Fig. 9, for the truck (100) to be maintained in the high speed state (152), the high speed/coast release switch

(115A) must remain activated. To relieve the operator of the truck (100) from having to hold the high speed/coast release switch (115A) to maintain operation of the truck (100) in the high speed state (152), which is objectionable to some operators, operation of the truck (100) in the high speed state (152) is maintained after the high speed/coast release switch (115A) is momentarily made and then released in the state diagram of Fig. 10. While in the high speed state (152), the truck can be operated at speeds up to either the intermediate speed or the high speed, depending upon the direction of movement of the truck, by means of the twist grips (118).

The low speed state (150) is entered from the high speed state (152) by releasing the high speed/coast release switch (115A) for the state diagram of Fig. 9.

For the state diagram of Fig. 10, the low speed state (150) is entered from the high speed state (152) by movement of the twist grips (118) into their central neutral positions to generate a zero (0) speed command or by application of the steerable wheel brake (117).

In the coast state (154), the speed of the truck (100) is limited to a low speed, such as walk speed, as previously noted. Also, entry into the coast state (154) activates the locking device (136), by engaging the electromagnet (140) in the illustrated embodiment, so that the steering arm (116) is locked into its then current position [or into a position to which it is subsequently moved while in the coast state (154)]. The coast state (154) is entered from either the low speed state (150) or the high speed state (152) by activation of the coast switch (115E) with the steering arm (116) in the truck run position, i. e., within the driving arc (123). While a single coast switch, i. e., the coast switch (115E), is illustrated as being mounted on the back of the control panel (115), the coast switch (115E) can be mounted elsewhere on the grab bar (112) or closely positioned to the grab bar (112). Alternately, two coast switches can also be used, one mounted on either side of the control panel (115) or at other locations on the grab bar (112) or otherwise associated with or closely positioned to the grab bar (112).

When in the coast state (154), if the high speed/coast release switch (115A) is activated or the reverser switch (120) is activated or the key is switched off and then back on, the controller (142) enters the low speed state (150). For the controller (142) to enter the high speed state (152) from the coast state (154), it first enters the low speed state (150) from which it can go to the high speed state (152) if the high speed/coast release switch (115A) is activated and a nonzero speed command is received from the twist grips (118), i. e., either of the twist grips (118) is moved out of its central neutral position.

With the understanding of the present invention gained from the above description of the novel locking device for overriding the deadman brake and the novel control of a deadman brake override system, operation of the truck (100) using the present invention will now be described. When an operator of the walkie/rider pallet truck (100) keys on the truck (100), the controller (142) comes up in the low speed state (150) so that the operator can move the truck (100) at speeds up to the limited low speed for the truck (100) by operation of the twist grips (118) or by activation of jog switches, if provided on a given truck. Once the truck (100) is keyed on, the operator proceeds with stock picking operations by moving the truck (100) along a prescribed route through a warehouse picking up stock in a predetermined sequence.

If the operator's first pick is a good distance from where the truck is keyed on, the operator steps onto the platform (110), grips the grab bar (112) immediately adjacent to the control panel (115) mounted on the grab bar (112), operates (continuously or momentarily) the high speed/coast release switch (115A) and moves one of the twist grips (118) to accelerate the truck (100) in a forward direction toward the first pick. These operations advance the controller (142) from the low speed state (150) to the high speed state (152) so that the truck (100) can be operated at speeds up to the high speed for the truck (100). Upon approaching the first pick, the operator moves the twist grip (118) to slow the truck (100) for the pick. Upon releasing the high speed/coast release switch (115A) or moving the twist grip (118) to its central neutral position, the controller (142) is placed into the low speed state (150).

As the truck (100) approaches the first pick, the operator brakes the truck (100) and steps from the platform (110). If the operator wants to coast the truck (100) to the first pick, he/she then activates the coast switch (115E) to place the controller (142) into the coast state (154) so that the steering arm (116) is locked into the position at which the coast switch (115E) was operated by activation of the electromagnet (140) (or other locking device). The operator then moves to the item to be picked, picks up the item and turns around as the truck (100) coasts into a position so that a pallet on the load forks (106) of the truck (100) [or other load support device on the forks (106) or provided in place of the load forks (106)] is in position for the operator to place the picked item thereon. The operator then advances the truck (100) to the next pick. If the next pick is close by, the operator walks along side the truck (100) and moves the truck (100) by twisting one of the twist grips (118) [or by activation of the jog switches (128) and/or (130) if jog switches are provided on the truck]. If the operator wants to change the vertical position of the steering arm (118) or handle (114) from that locked in when the coast mode of operation was engaged, he/she moves the handle (114) and thereby the steering arm (118) to a new desired position where it is retained by the locking device (136) until once again repositioned by the operator or the steering arm (118) is released by inactivating the coast mode of operation. Again, as the operator approaches the pick, he/she coasts the truck (100) to an appropriate position to place the pick onto the pallet on the forks (106) or other load support device of the truck (100).

If the next pick is some distance away, for example twenty or more feet, the operator may choose to step onto the platform (110) and ride the truck (100) to the next pick location. The operator would then engage the high speed/coast release switch (115A) to release the coast control and place the controller (142) into the low speed state (150). The activation of the high speed/coast release switch (115A) together with a nonzero speed command from the twist grips (118) moves the controller (142) through the low speed state (150) into the high speed state (152) so that the operator can move the truck (100) at speeds up to the high speed for the truck (100) to more rapidly advance the truck (100) to the next pick location. Upon approaching the next pick location, the operator would brake the truck (100) and

step from the platform (110). Presuming that the operator again wants to coast the truck (100) to the pick, the operator then manually actuates the coast switch (115E) to place the controller (142) into the coast state (154) so that the steering arm (118) is locked into the position at which the coast switch was operated by activation of the electromagnet (140) (or other locking device).

It is, thus, apparent that operation of the truck (100) for stock picking applications is improved since the coast mode of operation can be conveniently engaged by manual operation of the coast switch (115E) mounted on or near the grab bar (112). Once the coast mode of operation is engaged, the truck (100) can remain in the coast mode for two or more closely spaced picks. And, the truck (100) can be quickly changed from the coast mode to the high speed mode and back to the coast mode by manual operation of the high speed/coast release switch (115A) and the coast switch (115E). In addition, during operation of the truck (100) in the coast mode, an operator can readily select the position of the handle (114) in accordance with his or her preference and the position of the handle (114) can be readily changed to a new position as operating conditions or the operator's preference changes.

Having thus described the invention of the present application in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

What is claimed is: