Abstract
An apparatus for dispensing pallets from a stack is disclosed, designed to tolerate variations in pallet stringer board integrity and dimensions. It employs a tine-and-fork transfer mechanism that engages pallets without relying on precise stringer geometry, thereby preventing jams caused by damaged or non-standard stringers. The system includes a detection mechanism for identifying compromised pallets and a dedicated reject path. This arrangement facilitates automated handling of mixed pallet stacks, improving operational reliability in material handling systems where pallet quality is variable.
1. Technical Field
[0001]This disclosure relates to automated material handling systems, specifically to devices for dispensing individual pallets from a stacked arrangement, particularly addressing challenges presented by non-uniform or damaged pallets.
2. Technical Context
[0002]Automated pallet dispensing systems typically rely on consistent pallet dimensions and integrity to function reliably. Pallets often encounter wear and damage during their operational life, leading to broken stringer boards, missing deck boards, or variations in overall dimensions. Conventional pallet dispensers, which may utilize pushing mechanisms or lifting devices that engage specific pallet features, are susceptible to jamming when encountering such damaged or non-standard pallets. Jams disrupt material flow, require manual intervention, and reduce operational efficiency. There is a need for a pallet dispensing system that can tolerate a range of pallet conditions, including damaged stringer boards, to maintain continuous operation and reduce downtime.
3. System Overview
[0003]The disclosed system is a pallet dispenser configured to extract individual pallets from a vertical stack. It incorporates a unique tine-and-fork transfer mechanism designed to engage pallets resiliently, accommodating variations in stringer board integrity. The system includes a pallet stack support structure (10), a lifting and lowering mechanism (14), a pair of engaging tines (16), and a pair of support forks (18). A detection subsystem (20) evaluates the condition of the stringers as a pallet is being transferred. Pallets identified as having significant damage are directed to a reject path (22), while acceptable pallets are delivered to an outfeed conveyor (24). This approach minimizes operational interruptions caused by damaged pallets.
4. Components
[0004]The system comprises several key components, as illustrated in FIG. 1 and FIG. 2.
[0005]
- Pallet Stack Support Structure (10): This structure forms a frame designed to hold a vertical stack of pallets (11). It typically includes vertical guide rails or posts to maintain stack alignment. The structure is configured to allow the lowest pallet to be accessed by the transfer mechanism.
- Lifting and Lowering Mechanism (14): This mechanism is responsible for raising and lowering the entire pallet stack (11) as needed. It may consist of a hydraulic cylinder, an electric linear actuator, or a screw drive system, connected to a platform or lifting arms that support the stack from below. The mechanism ensures that the lowest pallet is presented at the correct elevation for engagement.
- Engaging Tines (16): A pair of horizontally oriented engaging tines (16) are mounted on a shuttle assembly (26) that can move horizontally. Each tine (16) has a tapered or chamfered leading edge (16a) designed to facilitate entry into the pallet's stringer openings. These tines (16) are positioned to enter the openings between the top and bottom deck boards of a pallet, specifically above the stringer boards.
- Support Forks (18): Positioned below the engaging tines (16), a pair of horizontally oriented support forks (18) are also mounted on the shuttle assembly (26). These forks (18) are designed to pass beneath the stringer boards of a pallet. The vertical distance between the engaging tines (16) and the support forks (18) is adjustable, or fixed to accommodate common pallet dimensions, to create a capture zone for the stringer boards.
- Shuttle Assembly (26): This assembly provides the controlled horizontal motion for both the engaging tines (16) and the support forks (18). It is typically driven by an electric motor (28) coupled to a belt, chain, or rack-and-pinion drive system. The shuttle assembly (26) enables the tines and forks to extend into the pallet and retract, carrying the pallet.
- Detection Subsystem (20): This subsystem is integrated with the transfer path and is designed to assess the integrity of the pallet stringer boards. It may consist of optical sensors (e.g., photo-electric beams, laser profilers) or mechanical probes (e.g., spring-loaded fingers) positioned to interact with the stringers as the pallet is being extracted. The sensors are configured to detect deviations from expected stringer dimensions or presence.
- Reject Path (22): A dedicated path for pallets deemed unsuitable. This path typically comprises a set of rollers or a short conveyor section that diverts rejected pallets away from the main outfeed. A divert gate (23) or movable section of conveyor can be used to direct pallets to this path.
- Outfeed Conveyor (24): This conveyor receives accepted pallets from the dispenser and transports them downstream for further processing. It may be a roller conveyor, belt conveyor, or chain conveyor.
- Control System (30): An industrial programmable logic controller (PLC) or similar control unit manages the sequence of operations, including the lifting mechanism, shuttle movement, detection subsystem, and divert gate. It receives input from sensors and controls actuators to ensure coordinated operation.
5. Operation
[0006]The operation of the pallet dispenser proceeds through several phases: stack presentation, pallet engagement, stringer assessment, and pallet discharge.
[0007]Start-up: Upon initiation, the control system (30) ensures the pallet stack support structure (10) is loaded with pallets. The lifting and lowering mechanism (14) elevates the stack (11) until the bottom pallet is positioned at the pick-up height, aligned with the entry plane of the engaging tines (16) and support forks (18).
[0008]Steady Running (Dispensing Cycle):
[0009]
- Stack Positioning: The lifting and lowering mechanism (14) ensures the bottom pallet of the stack (11) is correctly aligned for engagement. This may involve a slight lift and then a controlled lowering onto fixed stops or temporary supports, ensuring the pallet is stable.
- Tine and Fork Extension: The shuttle assembly (26) extends the engaging tines (16) and support forks (18) horizontally into the bottom pallet. The chamfered leading edges (16a) of the tines guide them into the pallet openings above the stringers. Simultaneously, the support forks (18) pass beneath the stringers. The vertical separation between the tines and forks is designed such that the pallet stringers are captured securely between them. This capture method allows for tolerance to minor variations in stringer height or small localized damage, as the tines engage the top deck boards and the forks support from below.
- Pallet Extraction and Lowering: Once fully inserted, the shuttle assembly (26) retracts, pulling the engaged pallet clear of the stack. As the pallet is extracted, the lifting and lowering mechanism (14) may slightly lower the remaining stack to prevent interference with the extracted pallet or to prepare for the next cycle.
- Stringer Assessment: As the extracted pallet moves horizontally on the shuttle assembly (26), it passes through the detection subsystem (20). Sensors within the detection subsystem (20) scan the stringer boards for integrity. For example, optical sensors might detect gaps or missing material, or mechanical probes might register the absence of expected resistance. The system evaluates these signals against predefined criteria for acceptable pallet condition.
- Discharge Decision: Based on the assessment, the control system (30) determines if the pallet is acceptable or requires rejection.
- Accepted Pallet: If the pallet meets the criteria, the divert gate (23) remains open to the outfeed conveyor (24). The shuttle assembly (26) continues its retraction movement, depositing the pallet onto the outfeed conveyor (24).
- Rejected Pallet: If the pallet is deemed unacceptable, the control system (30) activates the divert gate (23) to route the pallet to the reject path (22). The shuttle assembly (26) then deposits the pallet onto the reject path (22).
- Cycle Completion: After discharging the pallet, the shuttle assembly (26) returns to its home position, and the lifting and lowering mechanism (14) repositions the stack for the next cycle.
[0010]Fault or Interruption:
[0011]
- Jam Detection: If the engaging tines (16) or support forks (18) encounter excessive resistance during insertion, or if a pallet fails to clear the stack properly, sensors (e.g., motor current monitoring, limit switches) will detect a fault. The system will halt operation, retract the shuttle assembly (26) if safe, and signal an alarm. The control system (30) may attempt a recovery sequence, such as a slight repositioning, before fully stopping.
- Sensor Malfunction: A fault in the detection subsystem (20) may trigger a safe stop, or default to rejecting all pallets until the issue is resolved, depending on configuration.
- No Pallet Present: If the stack becomes empty, a sensor will detect this, and the system will enter a standby mode, signaling for replenishment.
6. Example Embodiments
[0012]Embodiment 1 In this embodiment, the engaging tines (16) and support forks (18) are integrated into a single, rigid C-shaped arm mechanism for each side of the pallet. The vertical gap between the upper and lower sections of the 'C' is fixed and sized to accommodate nominal stringer board thicknesses plus a tolerance. The detection subsystem (20) utilizes an array of through-beam photoelectric sensors mounted along the path where the pallet stringers pass. A break in the expected pattern of beams indicates a missing or severely damaged stringer segment. The reject path (22) is a simple gravity chute adjacent to the main conveyor, activated by a single pneumatic cylinder extending a stop arm.
[0013]Embodiment 2 This embodiment features independently actuated engaging tines (16) and support forks (18). Each tine and fork can be individually raised or lowered by a small actuator (e.g., pneumatic cylinder) allowing the vertical capture zone to dynamically adjust to varying pallet dimensions or to gently guide a misaligned stringer. The detection subsystem (20) employs laser triangulation sensors that profile the stringer's top surface as it passes. This provides a more detailed assessment of material presence and height variations, allowing for a more nuanced decision on pallet acceptability. The reject path (22) is a powered roller conveyor that diverges at a 30-degree angle from the main outfeed, controlled by a pivot section of the main conveyor.
[0014]Embodiment 3 This embodiment is designed for stacks of mixed pallet heights. The lifting and lowering mechanism (14) incorporates a sensor (e.g., ultrasonic distance sensor) that measures the height of the topmost pallet in the stack. Before each dispensing cycle, the mechanism adjusts the stack height to present the bottom pallet at a standardized engagement plane, regardless of the overall stack height variation. The engaging tines (16) and support forks (18) have slightly longer travel to ensure full engagement even if the pallet is slightly offset vertically. The detection subsystem (20) incorporates load cells on the support forks (18) to estimate the pallet's weight distribution, providing an indirect measure of stringer integrity, in addition to optical sensors.
7. Alternative Configurations
[0015]Instead of a single shuttle assembly (26) for horizontal movement, the engaging tines (16) and support forks (18) could be mounted on separate, synchronously controlled linear slides. This configuration might allow for independent adjustment of insertion speed or retraction force. The pallet stack support structure (10) could be designed as a cantilevered frame, allowing for pallet loading from three sides rather than just the top. The outfeed conveyor (24) might be replaced with a robotic pick-and-place station directly downstream from the dispenser. The detection subsystem (20) could utilize machine vision cameras to inspect stringer integrity, providing more comprehensive defect identification.
8. Parameter Variations
| Parameter | Range | Effect of Increasing Value | Effect of Decreasing Value |
|---|---|---|---|
| Shuttle Speed | 0.2 to 1.0 m/s | Faster cycle time, increased kinetic forces, higher wear | Slower cycle time, reduced impact forces, less wear |
| Tine-Fork Vertical Gap | 90 to 120 mm | Accommodates thicker stringers, looser capture | Tighter capture, potential for jamming with oversized stringers |
| Stack Height Capacity | 10 to 20 pallets | Requires taller lifting mechanism, increased stability needs | Shorter lifting mechanism, more frequent stack replenishment |
| Detection Threshold | 5 to 25% missing material | Fewer pallets rejected, higher risk of downstream issues | More pallets rejected, lower risk of downstream issues |
| Dispense Cycle Time | 8 to 20 seconds per pallet | Higher throughput, increased component stress | Lower throughput, gentler operation |
9. Additional Implementations
[0017]This pallet dispensing mechanism can be integrated into various automated material handling environments. For example, it can be positioned upstream of an automated palletizing robot, providing a continuous supply of qualified pallets. It could also be used in an automated storage and retrieval system (AS/RS) where pallets are staged for outbound shipping, ensuring that only structurally sound pallets enter the shipping stream. The detection subsystem (20) could be expanded to include RFID readers or barcode scanners to identify specific pallet types or track pallet usage data. Furthermore, the system could incorporate an automatic pallet re-stacker at the end of the reject path (22) to efficiently manage rejected pallets for repair or disposal, rather than requiring manual handling of individual rejected items. The engaging tines (16) and support forks (18) could be coated with a low-friction polymer to reduce wear and minimize damage to the pallet wood during insertion and extraction.
10. Figures
