Abstract
This disclosure describes a pallet layer transfer head configured for handling full layers of packaged goods, such as cartons. It incorporates independently actuated side clamping mechanisms and a compliant layer contact surface. The arrangement addresses the problem of layer instability and collapse that can occur when a rigid transfer head releases an uneven or loosely packed layer, particularly at the periphery. The design ensures controlled support during transfer and a sequenced, controlled release to maintain layer integrity.
1. Technical Field
[0001]This disclosure relates to automated material handling systems, specifically to apparatus for transferring a full layer of articles, such as packaged goods or cartons, from one location to another, typically within a palletizing or depalletizing operation.
2. Technical Context
[0002]In automated material handling, particularly in palletizing and depalletizing operations, it is common to transfer an entire layer of articles simultaneously. These layers can consist of multiple individual packages, cartons, or other items arranged in a predefined pattern. A common challenge arises when the articles within a layer are not perfectly uniform in size, are loosely packed, or have low inherent stability when unconstrained. When a transfer head, especially one with rigid clamping surfaces, attempts to release such a layer, the uneven distribution of forces or asynchronous retraction of clamping elements can lead to a sudden loss of support for some articles before others. This can cause peripheral articles to topple or the entire layer to become unstable and collapse, leading to product damage, line stoppages, and reduced throughput. Existing solutions often rely on precise placement or high friction, which may not be sufficient for inherently unstable layer configurations.
3. System Overview
[0003]The disclosed arrangement is a pallet layer transfer head (10) designed to handle and transfer a complete layer of articles while maintaining layer integrity, particularly during release. The transfer head (10) comprises a main frame (12), a top contact surface (14), and multiple independently actuatable side clamp assemblies (16). The top contact surface (14) incorporates compliant elements to adapt to minor variations in the top surface of the article layer. Each side clamp assembly (16) includes a clamp face (18) that engages the sides of the article layer. A height sensing mechanism (20) determines the vertical extent of the article layer to ensure proper engagement. Control logic (22) manages the sequencing of clamp actuation and release, prioritizing sustained support for outer articles during the final stages of release. The transfer head (10) is designed to be mounted on a robotic arm or gantry system (not shown) for movement between pick-up and deposit locations.
4. Components
[0004]
- Main Frame (12): This structural component provides the rigid backbone of the transfer head (10), to which all other components are mounted. It is typically constructed from welded steel or aluminum profiles, designed for stiffness and minimal deflection under load. Mounting points for attachment to a robotic manipulator or gantry are integral to the main frame (12).
- Top Contact Surface (14): Positioned beneath the main frame (12), this surface makes contact with the top of the article layer. It comprises an array of compliant elements (24), such as pneumatic bladders, foam pads, or spring-loaded plates, which can deform to conform to the irregular top surface of the layer. This ensures uniform downward pressure distribution across the layer. The compliant elements (24) are typically covered by a durable, low-friction membrane.
- Side Clamp Assemblies (16): Multiple side clamp assemblies (16) are mounted to the main frame (12), usually along the perimeter of the head. Each assembly includes a clamp face (18) and an actuation mechanism (26). The clamp faces (18) are typically flat plates made of a low-friction material or incorporate a high-friction coating depending on article surface properties. The actuation mechanism (26) for each assembly is independent, allowing individual or coordinated movement. Common actuation mechanisms include pneumatic cylinders, electric linear actuators, or hydraulic cylinders.
- Clamp Face (18): This is the part of the side clamp assembly (16) that directly contacts the side of the article layer. The clamp face (18) may incorporate a compliant lining (28), such as a layer of rubber or foam, to absorb minor irregularities in the article side surfaces and distribute clamping force more evenly. The compliance helps to prevent localized stress concentrations on individual articles.
- Height Sensing Mechanism (20): This mechanism measures the vertical dimension of the article layer. It may consist of non-contact sensors, such as ultrasonic or laser distance sensors, mounted on the main frame (12), or mechanical feeler gauges that contact the layer. The data from the height sensing mechanism (20) informs the control logic (22) about the appropriate clamping depth and top surface engagement. As shown in FIG. 1, sensors (20) are positioned to measure the layer height prior to full engagement.
- Control Logic (22): An electronic controller, such as a programmable logic controller (PLC), manages all operational sequences. It receives inputs from sensors, including the height sensing mechanism (20) and clamp position sensors (not shown), and outputs commands to the actuation mechanisms (26) of the side clamps (16) and any top surface engagement mechanism. The control logic (22) executes the programmed clamping and release sequences.
- Actuation Mechanism (26): For each side clamp assembly (16), this mechanism provides the force and motion to extend and retract the clamp face (18). It is typically a pneumatic cylinder for fast response and adjustable force, or an electric servo actuator for precise position and force control.
5. Operation
[0005]The operation of the pallet layer transfer head (10) involves a sequence of stages: approach, engagement, transfer, and release.
[0006]Start and Approach: The transfer head (10), typically carried by a robot or gantry, moves to a position above the article layer to be transferred. During this approach, all side clamp assemblies (16) are fully retracted. The height sensing mechanism (20) begins to acquire data as the head descends, determining the exact height of the article layer.
[0007]Engagement: Once the transfer head (10) is positioned just above the layer, the top contact surface (14) descends to gently rest upon the articles. The compliant elements (24) conform to the layer's upper profile. Simultaneously or shortly thereafter, the side clamp assemblies (16) begin to extend. The control logic (22) ensures that the clamp faces (18) extend inward until a predefined clamping force or position is achieved against the sides of the article layer. The independent actuation allows for slight variations in layer dimensions or article positions across the layer to be accommodated by each clamp assembly (16) adjusting its extension. This firmly secures the perimeter of the layer.
[0008]Transfer: With the layer fully engaged by both the top contact surface (14) and the side clamp assemblies (16), the transfer head (10) lifts the layer. The robot or gantry then moves the secured layer to the target deposit location, such as another pallet or a conveyor.
[0009]Release: Upon arrival at the deposit location, the transfer head (10) lowers the layer onto the receiving surface. Once the layer is fully supported by the destination surface, the release sequence begins. This sequence is critical for maintaining layer stability. First, the top contact surface (14) is disengaged by retracting slightly upwards. Then, the side clamp assemblies (16) retract. To prevent collapse of unstable periphery articles, the retraction is sequenced. The inner-most side clamp assemblies (16) or those deemed less critical for overall layer stability may retract first. The outermost side clamp assemblies (16), particularly those supporting corners or edges of the layer, retract last, ensuring these critical points of support are maintained for the longest possible duration. This staged retraction minimizes the risk of article toppling. Once all clamps are fully retracted, the transfer head (10) lifts clear of the deposited layer and returns to its home position or begins the next cycle.
[0010]Fault or Interruption: In the event of a fault, such as an article misalignment detected by sensors (not shown) or an emergency stop, the control logic (22) will halt all motion. If the layer is currently being held, the clamps will typically remain engaged to secure the layer until the fault is cleared or a safe recovery procedure is initiated. If the fault occurs during release, the release sequence may be paused or reversed to re-engage the clamps, depending on the system's safety protocols.
6. Example Embodiments
[0011]Embodiment 1 In this embodiment, the top contact surface (14) consists of a single large pneumatic bladder (24) covered by a durable, anti-friction fabric. Air pressure within the bladder is controlled by a proportional valve to apply a consistent downward force across the layer. The side clamp assemblies (16) use pneumatic cylinders (26) for actuation, with each cylinder having an integrated pressure sensor to monitor clamping force. The height sensing mechanism (20) comprises an array of four ultrasonic sensors mounted at the corners of the main frame (12), providing an averaged layer height. Release sequencing is based on pre-programmed delays, retracting the two shorter sides of the layer first, followed by the two longer sides, with a 50 ms delay between each pair of sides. This configuration is depicted in FIG. 2, showing the side clamps (16) and their actuation mechanisms (26).
[0012]Embodiment 2 This embodiment utilizes a top contact surface (14) composed of a grid of independent, spring-loaded plates (24), each covered with a high-friction elastomer. This passive compliance adapts to layer variations. The side clamp assemblies (16) employ electric linear servo actuators (26) which allow for precise control of clamp face (18) position and applied force, with position feedback from encoders. The clamp faces (18) include a 5 mm thick compliant foam lining (28). A single laser distance sensor (20) mounted centrally on the main frame (12) measures layer height. The control logic (22) implements a release sequence where corner clamps retract last, after all middle clamps have fully disengaged. This provides maximum stability at the layer's extremities during the critical final moments of release.
[0013]Embodiment 3 In this embodiment, the transfer head (10) incorporates a vacuum assist feature in addition to mechanical clamping. The top contact surface (14) consists of a perforated plate with an integrated vacuum plenum, allowing for suction cups (not shown) or a vacuum chamber effect to aid in securing the layer from above. The primary side clamp assemblies (16) are hydraulically actuated (26), providing high clamping forces suitable for heavy or very unstable layers. The clamp faces (18) are rigid but are angled slightly inwards (e.g., 2 degrees) to provide a wedging action. The height sensing mechanism (20) uses physical contact probes that trigger micro-switches to establish the top surface level. The release sequence involves a gradual, synchronized retraction of all side clamps (16) at a controlled velocity, while the vacuum assist is maintained until all mechanical clamps are fully disengaged, after which the vacuum is released.
7. Alternative Configurations
[0014]The top contact surface (14) could alternatively employ an array of small, individually actuated suction cups, each controlled by a miniature solenoid valve, providing localized vacuum for uneven top surfaces. The side clamp actuation mechanisms (26) could be cam-driven systems, where a rotating cam pushes or pulls the clamp faces (18) into position, offering a mechanically synchronized movement. The height sensing mechanism (20) could be integrated into the side clamp assemblies (16) themselves, with the initial contact of the clamp face (18) against the article layer providing vertical position feedback. The clamp faces (18) could be designed with a textured or patterned surface to increase friction with the articles, rather than relying on a separate compliant lining (28).
8. Parameter Variations
| Parameter | Range | Effect of Increasing Value | Effect of Decreasing Value |
|---|---|---|---|
| Clamp actuation speed | 50 to 500 mm/s | Faster engagement/release, higher dynamic loads | Slower operation, reduced dynamic loads |
| Clamp force per side | 50 to 5000 N | Increased grip, risk of article deformation | Reduced grip, potential for layer slippage |
| Compliance thickness (face) | 2 to 20 mm | Greater accommodation of article variation, softer grip | Less accommodation, more rigid grip, higher localized pressure |
| Top surface pressure | 5 to 50 kPa | Stronger downward hold, potential for article crushing | Weaker downward hold, risk of article shifting |
| Release sequence delay | 0 to 500 ms between stages | Slower, more controlled release, longer cycle time | Faster release, increased risk of instability |
| Number of side clamps | 2 to 8 | More distributed support, increased complexity | Less distributed support, simpler design |
9. Additional Implementations
[0016]The described transfer head (10) can be augmented with additional features. For instance, a vision system comprising a camera (not shown) could be integrated into the main frame (12) to inspect the layer pattern for integrity or missing articles before transfer. This system could also guide precise placement. For layers of articles with non-rectangular footprints, the clamp faces (18) could be articulated or segmented to conform to a curved or irregular layer perimeter. The compliant elements (24) of the top contact surface (14) could incorporate heating or cooling elements for temperature-sensitive articles, maintaining product integrity during transfer. Furthermore, a blow-off system using compressed air nozzles could be integrated into the periphery of the transfer head (10) to assist in cleanly separating the layer from the pick-up surface or to ensure precise placement on the deposit surface by creating a small air cushion underneath the layer as it is lowered. The control logic (22) could be adaptive, learning optimal clamping forces and release sequences based on sensor feedback from previous successful transfers, adjusting parameters in real-time to handle variations in product batches.
10. Figures
