Abstract
A pallet layer transfer head is described for handling layers of articles, such as cartons, which may exhibit instability. The arrangement incorporates independently retractable side clamps designed to maintain support for the outermost articles during layer release. This addresses the problem where a conventional, rigid clamp head releases unevenly, leading to the collapse or disarray of unstable layers. The design includes features for precise clamp sequencing, compliant contact with article surfaces, and adaptive layer height sensing, ensuring controlled and stable transfer operations. The sequential release mechanism prioritizes continuous support for peripheral articles, mitigating layer collapse.
1. Technical Field
[0001]This disclosure relates to material handling equipment, specifically to apparatus for transferring a full layer of articles, such as packaged goods or cartons, from one location to another, typically onto or off a pallet or slip sheet.
2. Technical Context
[0002]In industrial packaging and warehousing operations, layers of articles are often formed and then transferred as a unit. These layers can consist of cartons or other packages stacked in a specific pattern. A common challenge arises when the articles within a layer are not inherently stable, meaning they may shift or topple if external support is removed unevenly. Conventional layer transfer heads often employ a perimeter clamping mechanism that releases all sides simultaneously or in a fixed sequence that does not account for the inherent instability of the layer. When such a head releases an unstable layer, particularly if the clamping force or contact is not uniform across the layer's periphery, the outermost articles can lose support prematurely. This can lead to the collapse or disarray of the layer, resulting in product damage, operational delays, and potential safety hazards. The need exists for a layer transfer head capable of maintaining continuous, controlled support for unstable layers during the entire transfer and release cycle, particularly for the articles located at the periphery of the layer.
3. System Overview
[0003]The disclosed system is a pallet layer transfer head (10) configured to grasp, lift, transport, and release a full layer of articles (100). The head (10) includes a main frame (12) that provides structural integrity and attachment points for other components. A central vacuum manifold (14) with an array of vacuum cups (16) is mounted beneath the main frame (12) to provide primary vertical lifting force. Surrounding the vacuum manifold (14) are multiple independently actuated side clamping mechanisms (18). Each clamping mechanism (18) comprises a clamp arm (20) with a compliant clamp face (22) and an actuator (24), such as a pneumatic cylinder or electric linear actuator, enabling the arm (20) to extend and retract independently. A layer height sensing system (26), which may include optical sensors or proximity sensors, is integrated into the head (10) to determine the precise vertical position of the article layer (100) before clamping. A control system (28) manages the sequencing of the vacuum system (30), the clamp actuators (24), and the layer height sensing system (26). The control system (28) executes a specific release sequence designed to progressively reduce support while maintaining stability for peripheral articles until the layer (100) is fully settled. The entire head (10) is typically connected to a gantry or robotic arm (32) for movement. FIG. 1 illustrates a high-level block diagram of the system components and their interconnections.
4. Components
[0004]Main Frame (12): This structural element provides the rigid foundation for the layer transfer head (10). It is typically fabricated from welded structural steel or aluminum profiles, designed to withstand the combined weight of the article layer (100) and the operational forces of the clamping mechanisms (18) and vacuum system (30). Attachment points are provided for connection to a lifting mechanism (32).
[0005]Central Vacuum Manifold (14): A plenum chamber connected to a vacuum source (30). It distributes vacuum pressure to an array of vacuum cups (16) positioned across the central area of the head's underside. The manifold (14) is constructed to maintain a sufficient vacuum level for lifting the layer (100).
[0006]Vacuum Cups (16): Multiple suction cups, typically made of elastomeric material, are attached to the vacuum manifold (14). These cups (16) create a primary lifting force by engaging with the top surface of the article layer (100) when vacuum is applied. The number and arrangement of cups are determined by the size and weight of the layers to be handled, with typical diameters ranging from 80 mm to 200 mm.
[0007]Side Clamping Mechanisms (18): These are assemblies positioned around the perimeter of the vacuum manifold (14). Each mechanism (18) consists of a clamp arm (20), a compliant clamp face (22), and an actuator (24).
[0008]Clamp Arm (20): A rigid mechanical arm that extends horizontally to contact the sides of the article layer (100). The arm (20) is designed to transmit force from the actuator (24) to the clamp face (22). Multiple arms (20) are typically arranged along each side of the head (10) or as single, continuous arms covering an entire side.
[0009]Compliant Clamp Face (22): The part of the clamp arm (20) that directly contacts the articles (100). This face (22) is covered with a material such as high-friction rubber, open-cell foam, or a segmented resilient pad. The compliance of this material allows it to conform to minor irregularities in the article surfaces, distribute clamping pressure more evenly, and absorb minor impacts during engagement. The durometer of the material may be specified between 30 and 60 Shore A.
[0010]Actuator (24): A device responsible for extending and retracting each clamp arm (20) independently. These can be pneumatic cylinders, electric linear actuators, or servomotors driving lead screws. Each actuator (24) provides precise control over the clamping force and position of its associated clamp arm (20).
[0011]Layer Height Sensing System (26): A set of sensors mounted on the main frame (12) that detect the vertical position of the top surface of the article layer (100) and the general height of the layer (100) prior to clamping. These may include diffuse-reflective optical sensors, ultrasonic sensors, or laser displacement sensors. The system (26) provides data to the control system (28) for adaptive clamping and release.
[0012]Control System (28): A programmable logic controller (PLC) or industrial PC that orchestrates the operation of all components. It receives input from the layer height sensing system (26), manages the vacuum system (30), and precisely controls the extension, retraction, and force of each actuator (24) according to predefined or adaptive sequences.
[0013]Vacuum System (30): Includes a vacuum pump, manifold (14), vacuum lines, and control valves (34). It generates and regulates the vacuum pressure supplied to the vacuum cups (16).
[0014]Gantry or Robotic Arm (32): The mechanism to which the layer transfer head (10) is affixed, providing translational and rotational movement for positioning the head (10) over the source and destination locations. This is typically an overhead gantry crane, a robotic manipulator, or a palletizer's main arm.
5. Operation
[0015]Start-up and Approach: Upon activation, the control system (28) initializes all components. The gantry or robotic arm (32) positions the layer transfer head (10) above the article layer (100) to be transferred. The layer height sensing system (26) measures the height of the layer (100) relative to the head (10).
[0016]Grasping Sequence: Based on the sensed layer height, the head (10) descends. As the vacuum cups (16) make contact with the top surface of the layer (100), the vacuum system (30) is activated, engaging the primary lifting mechanism. Simultaneously or immediately thereafter, the actuators (24) extend the side clamp arms (20), bringing the compliant clamp faces (22) into contact with the sides of the layer (100). The clamping force is applied to secure the layer (100) laterally. The sequence of clamp extension can be simultaneous for all sides or in a predefined order, for instance, first the longer sides then the shorter sides, to square the layer (100).
[0017]Lift and Transport: Once the layer (100) is securely grasped by both vacuum and side clamps, the gantry or robotic arm (32) lifts the head (10) and transports the layer (100) to the destination, such as an empty pallet or another layer on a stack.
[0018]Release Sequence: This is a critical phase for unstable layers. The head (10) descends to place the layer (100) onto the destination surface. As the layer (100) settles, the vacuum force from the vacuum cups (16) is maintained, continuing to hold the layer (100) down against the destination surface. The control system (28) then initiates a sequential retraction of the side clamping mechanisms (18). The retraction order is programmed to maintain lateral support for the most vulnerable parts of the layer (100) for the longest duration. Typically, this means the clamps on the inner perimeter (e.g., those supporting cartons that are less likely to tip) retract first. The outermost clamps, especially those supporting articles at corners or exposed edges, retract last. For example, on a rectangular layer, the clamps on the long sides might retract first, followed by the clamps on the short sides, then finally the corner clamps. This progressive release ensures that as support is removed, the articles (100) are already settled under their own weight and the residual vacuum holding, minimizing the chance of collapse. The compliant clamp faces (22) assist in a smooth disengagement.
[0019]Disengagement: After all side clamps (18) have fully retracted, the vacuum is released by opening the vacuum valves (34). The head (10) then ascends, separating from the now fully released layer (100). The system (10) is then ready for the next cycle or returns to a home position.
[0020]Fault or Interruption: In the event of a fault, such as a vacuum loss, sensor error, or emergency stop, the control system (28) is configured to safely abort the operation. If a layer (100) is being held, it may be lowered to the nearest stable surface (e.g., the source or destination pallet) and released under controlled conditions, or held securely in place until manual intervention is possible. Alarms are triggered to alert operators. The independent actuation of the side clamps (18) allows for individual retraction if a specific clamp malfunctions, potentially preventing complete layer collapse.
6. Example Embodiments
[0021]Embodiment 1: A layer transfer head (10) configured with four distinct side clamping mechanisms (18), one for each side of a rectangular layer of articles (100). Each mechanism (18) consists of a single, continuous clamp arm (20) extending along the entire length of its respective side, driven by two pneumatic cylinders (24) for parallel extension and retraction. The compliant clamp face (22) is a continuous strip of closed-cell foam with a durometer of 40 Shore A. The release sequence is programmed such that the two longer side clamps (18) retract simultaneously, followed by the two shorter side clamps (18) retracting simultaneously. The vacuum is maintained until all clamps are clear.
[0022]Embodiment 2: A layer transfer head (10) designed for handling layers (100) with varying dimensions, incorporating multiple segmented clamp arms (20) along each side, for example, three segments per long side and two per short side. Each segment is independently actuated by a small electric linear actuator (24). The compliant clamp face (22) on each segment is a modular rubber pad. The layer height sensing system (26) uses laser displacement sensors to map the layer profile. The control system (28) dynamically adjusts the clamping pressure of each segment based on the detected layer stability and initiates a progressive release where peripheral segments at corners retract last, followed by central segments along the short sides, and then central segments along the long sides.
[0023]Embodiment 3: A layer transfer head (10) featuring four main side clamps (18) for the periphery and an additional set of four corner clamps (36), each independently actuated. The corner clamps (36) are specifically designed to grasp the outermost articles (100) at the layer's corners. The compliant clamp faces (22) on all clamps are textured silicone pads. The release sequence prioritizes the corner clamps (36) as the very last to retract, after the main side clamps (18) have disengaged, providing maximum stability to the layer's most vulnerable points. The vacuum is released only after all side and corner clamps (18, 36) are fully retracted.
7. Alternative Configurations
[0024]Instead of a central vacuum manifold (14), the primary lifting force could be provided by a large number of individual vacuum ejectors connected to each vacuum cup (16), allowing for individual cup control or zones of control. The side clamping mechanisms (18) could employ cam-driven linkages instead of linear actuators (24), offering a mechanical advantage for clamping force. The compliant clamp face (22) material could be a series of inflatable bladders that conform to the article surfaces when pressurized. The layer height sensing system (26) could incorporate through-beam optical sensors at multiple heights to verify layer presence and height.
8. Parameter Variations
| Parameter | Range | Effect of Moving Towards Lower End | Effect of Moving Towards Higher End |
|---|---|---|---|
| Number of independent clamp mechanisms (18) | 4 to 12 | Reduced granularity of support; simpler control. | Enhanced localized support; increased complexity and cost. |
| Clamp face compliance (22) durometer | 30 to 70 Shore A | Higher conformability; better grip on irregular surfaces. | Increased rigidity; faster response to clamping/release. |
| Actuator (24) speed | 100 to 500 mm/s | Slower cycle time; gentler clamping and release. | Faster cycle time; potential for abrupt article movement. |
| Vacuum level (30) during hold | -30 kPa to -80 kPa | Reduced lifting capacity; less firm hold on layer. | Increased lifting capacity; tighter hold; higher energy consumption. |
| Layer height sensor (26) resolution | 1 mm to 10 mm | More precise layer height detection; better adaptive control. | Faster sensing; less precise height data; reduced adaptive capability. |
| Release sequence steps | 2 to 6 steps | Simpler programming; less granular control over stability. | Finer control over article stability during release; more complex logic. |
9. Additional Implementations
[0026]The described layer transfer head (10) can be adapted for handling layers of articles (100) that are not rectangular, such as circular or irregular shapes, by configuring the side clamping mechanisms (18) and their associated clamp arms (20) to conform to the specific perimeter. For instance, a head (10) for circular layers might employ radially actuated clamp arms (20). The control system (28) can incorporate force feedback from the actuators (24) to ensure that the clamping force applied to the layer (100) is within a safe range for the articles, preventing crushing or deformation. This feedback can also be used to detect partially collapsed layers or missing articles within the layer (100). The head (10) can also integrate an overhead camera system (38) for vision-based inspection of the layer pattern before grasping and after release, providing an additional layer of quality control and verification of layer integrity. Furthermore, a mechanism for actively vibrating the layer (100) during release could be incorporated to aid in settling the articles, especially those with high coefficients of friction or complex interlocking patterns. The head (10) could also be designed with integrated weigh scales to verify the total weight of the layer (100) before transport, aiding in inventory management and fault detection. FIG. 2 presents an elevation view of a pallet layer transfer head, illustrating key components.
10. Figures
