Abstract
A system for precise article induction onto a cross belt sorter carrier is disclosed. It addresses the problem of articles being misaligned, dropped, or split across multiple carriers due to induction timing that is not precisely synchronized with the physical position and pitch of the carriers. The arrangement utilizes an encoder system to derive induction timing windows directly from carrier pitch, ensuring articles are placed centrally onto individual carriers. Mechanisms for handling missed inductions and for carriers to report persistent loads beyond discharge points are also described.
1. Technical Field
[0001]This disclosure relates to material handling systems, specifically to sortation systems utilizing cross belt carriers for transporting and diverting articles.
2. Technical Context
[0002]Automated sortation systems are employed in various industries for processing and directing discrete articles. Cross belt sorters are a common type of high-speed sortation equipment where individual articles are placed onto moving carriers, each equipped with a transverse belt. The article is then transported by the carrier to a designated discharge location where the transverse belt activates to push the article off the main conveyor path. A critical aspect of such systems is the precise timing of article induction, which is the process of loading an article onto a carrier. If induction timing is not accurately synchronized with the carrier's position and velocity, articles may be dropped between carriers, misaligned on a single carrier, or landed across the gap between two adjacent carriers. Such errors can lead to system jams, damage to articles, or incorrect sortation.
3. System Overview
[0003]The disclosed system provides a method for synchronizing article induction with the physical pitch of carriers on a cross belt sorter. The system comprises a main conveyor (10) that transports a continuous chain of individual carriers (12). Each carrier (12) includes a cross belt (14) for article conveyance and discharge. An induction station (16) is positioned upstream of the main sortation path, configured to present articles (18) for loading onto the carriers (12). A primary encoder (20) is coupled to the main conveyor (10) drive system, providing high-resolution position feedback. This feedback is processed by a control unit (22) to determine the precise location of each carrier (12) and to define dynamic induction windows. An article sensor (24) detects the presence of an article (18) awaiting induction. The control unit (22) uses the carrier position data to trigger the release of an article (18) from the induction station (16) such that the article lands centrally on a target carrier (12). The system also incorporates mechanisms for detecting and managing missed inductions and for carriers to signal a persistent load state post-discharge.
4. Components
[0004]
- Main Conveyor (10): This forms the primary transport medium for the carriers (12). It typically consists of a chain or belt driven by a motor (26) and guided by a track or frame. The conveyor speed can range from 1.5 to 4.0 meters per second.
- Carrier (12): Each carrier is an individual unit designed to transport an article (18). It includes a frame, wheels or sliders that engage with the main conveyor (10) track, and an integrated cross belt (14). The carriers are typically linked to form a continuous train with a defined pitch, for example, 400 to 800 mm center-to-center.
- Cross Belt (14): Mounted on each carrier (12), this short conveyor belt runs perpendicular to the main conveyor's direction of travel. It is powered by an onboard motor or by an external linear motor segment at discharge points. The cross belt (14) facilitates the transfer of the article (18) onto and off the carrier (12).
- Induction Station (16): This is the mechanism responsible for presenting articles (18) to the carriers (12). It may comprise a feed conveyor, a metering belt, or a push-off device. The induction station (16) is controlled to release articles (18) at specific times to align with arriving carriers (12).
- Article (18): The item being sorted, which could be a package, parcel, or tote. Articles typically have a maximum dimension of 600 mm in length and width, and a weight up to 30 kg.
- Primary Encoder (20): A rotary or linear encoder coupled directly to the main conveyor (10) drive shaft or mechanism. It generates a high-resolution pulse train proportional to the movement of the main conveyor (10). For example, an encoder (20) may provide 10,000 to 50,000 pulses per revolution of a drive pulley, or 100 to 500 pulses per millimeter of linear travel.
- Control Unit (22): A programmable logic controller (PLC) or industrial PC that receives input from the primary encoder (20), article sensors (24), and other system components. It executes logic to determine carrier positions, calculate induction windows, control the induction station (16), and manage system faults. The control unit (22) typically operates with a scan time of 1 to 10 milliseconds.
- Article Sensor (24): A photoelectric sensor, proximity sensor, or vision system positioned at the induction station (16) to detect the presence of an article (18) ready for induction. It reports the article's presence to the control unit (22).
- Carrier Position Sensor (28): A sensor, such as an inductive proximity sensor or a magnetic sensor, mounted along the conveyor path. It detects a fiducial mark (e.g., a metal flag or magnet) on each carrier (12) or on the conveyor chain at a known interval. This sensor (28) provides a coarse but reliable carrier count and position verification, which can be used to recalibrate or verify the encoder (20) readings periodically. For example, a sensor (28) might be placed every 10 meters along the track.
- Onboard Load Sensor (30): Each carrier (12) can be equipped with a sensor, such as an infrared emitter/receiver pair or a load cell, to detect if an article (18) is present on its cross belt (14). This sensor (30) is typically read wirelessly or through contact brushes at specific points along the conveyor path.
5. Operation
[0005]The system operation begins with the main conveyor (10) transporting carriers (12) at a constant or variable speed. The primary encoder (20) continuously reports the incremental position of the main conveyor (10) to the control unit (22). The control unit (22) maintains a virtual map of carrier positions based on these encoder (20) pulses and a known carrier pitch. The carrier position sensor (28) provides periodic synchronization points to correct any accumulated encoder drift or to re-establish carrier identity after a system reset. For example, every 50 carriers, a unique carrier mark triggers the sensor (28) to confirm the count. Referring to FIG. 1, an article (18) arrives at the induction station (16) and is detected by the article sensor (24). The control unit (22) identifies the next available carrier (12) by predicting its arrival at the induction point based on encoder (20) data. An induction window is defined as the period during which an article (18) can be released from the induction station (16) to land squarely on the target carrier (12). This window is dynamically calculated based on carrier speed, article release trajectory, and carrier pitch. For instance, the window might open when the leading edge of the target carrier (12) is 150 mm upstream of the release point and close when the trailing edge is 50 mm downstream. When the precise moment within this window arrives, the control unit (22) commands the induction station (16) to release the article (18).
[0006]During steady running, the system continuously monitors carrier positions and synchronizes article release. If an article (18) is queued at the induction station (16) but no carrier (12) is available within the calculated time window (e.g., due to an empty slot or a carrier passing too quickly), or if the article (18) fails to be released by the induction station (16) when commanded, a missed induction event is registered. The control unit (22) logs this event and can either divert the missed article (18) to a reject lane or hold it for the next available induction opportunity, depending on system configuration. This is typically managed by a downstream sensor that confirms induction success. If a target carrier (12) passes the induction point without receiving an article when one was expected, the control unit (22) signals a missed induction.
[0007]On fault or interruption, such as an emergency stop, the primary encoder (20) ceases to provide pulses. The control unit (22) records the last known positions of all carriers (12). Upon system restart, the control unit (22) may require a homing sequence or may use the carrier position sensors (28) to re-establish absolute carrier positions before resuming synchronized operation. If a carrier (12) successfully discharges an article (18) at a sortation chute, its onboard load sensor (30) should indicate an empty state. However, if the onboard load sensor (30) reports that the carrier (12) is still loaded after passing its designated discharge point, this information is transmitted back to the control unit (22). This can occur via wireless communication, RFID tag reads, or physical contact brushes along the track. The control unit (22) then flags that carrier (12) as potentially problematic, potentially diverting it to a recirculation loop or a manual inspection station, or initiating a re-attempted discharge at a subsequent chute if available. Referring to FIG. 2, the onboard load sensor (30) data is typically polled at regular intervals or at specific read points along the conveyor path.
6. Example Embodiments
[0008]Embodiment 1 In this embodiment, the primary encoder (20) is a high-resolution rotary encoder directly coupled to the main drive shaft of the conveyor (10). The control unit (22) maintains a precise count of encoder pulses. The carrier pitch is known, for example, 500 mm. The control unit (22) identifies the leading edge of each carrier (12) by counting a specific number of pulses from a reference point (e.g., after the carrier position sensor (28) detects a fiducial mark on a known carrier). The induction window for an article (18) is calculated to begin 100 mm after the leading edge of the target carrier (12) passes the induction station's (16) article release point, and to end 100 mm before the trailing edge passes that same point. This ensures the article (18) lands within the central 300 mm of a 500 mm carrier (12). Missed inductions are detected by a downstream photo-eye that confirms an article (18) presence on the target carrier (12); if absent, the article (18) is directed to a reject lane from the induction station (16) for reprocessing.
[0009]Embodiment 2 This embodiment utilizes a linear encoder (20) mounted along the main conveyor (10) path, providing absolute position feedback for the conveyor chain. Each carrier (12) has a unique identification tag (e.g., RFID) read by a reader at the induction station (16). The control unit (22) correlates the RFID read event with the linear encoder (20) position to precisely map each carrier's (12) absolute position. The induction window is defined as a fixed linear distance relative to the carrier's (12) center point. If the article sensor (24) detects an article (18) but the induction command is not executed (e.g., due to a feeder fault), the control unit (22) flags the particular carrier (12) as having a missed induction. Carriers (12) reporting a persistent load past discharge use a simple weight sensor integrated into the carrier frame that signals its state via a radio frequency transmitter when passing over a designated receiver antenna.
[0010]Embodiment 3 In this embodiment, the primary encoder (20) is a virtual encoder derived from a servo motor's drive feedback system, providing precise motor shaft position. The carrier (12) pitch is variable, adjusted dynamically by the system for different article sizes. The control unit (22) calculates the induction window in real-time based on the current carrier pitch and speed, ensuring the article (18) always lands within the central 70% of the available carrier (12) surface. Upon a missed induction, the control unit (22) logs the article's (18) identifier and its intended destination. The article (18) is then held at the induction station (16) and re-attempted on the next available carrier (12) for which it is correctly sized. Carriers (12) with persistent loads are identified by an optical sensor located beneath the conveyor path at specific points, detecting the physical presence of an article (18) from below after the discharge area.
7. Alternative Configurations
[0011]Instead of a single primary encoder (20), an array of distributed sensors could be used to track individual carrier (12) positions. For instance, an optical system could image the conveyor belt or chain and use pattern recognition to track carrier (12) movement and derive pitch. The induction station (16) could employ a dynamically adjustable article release mechanism, such as a robotic arm or a variable-speed belt, to compensate for minor variations in carrier (12) speed or position, effectively widening the usable induction window. The carrier (12) onboard load sensor (30) could be a simple mechanical flag that is depressed by an article (18) and detected by a fixed proximity sensor at read points, rather than an active electronic sensor.
8. Parameter Variations
| Parameter | Realistic Range | Effect of Moving Towards Lower End | Effect of Moving Towards Upper End |
|---|---|---|---|
| Main Conveyor Speed | 1.5 to 4.0 m/s | Reduced throughput, longer induction windows for a given article length. | Increased throughput, shorter induction windows, higher precision required. |
| Carrier Pitch | 400 to 800 mm | More carriers per unit length, smaller article capacity, more frequent induction events. | Fewer carriers per unit length, larger article capacity, less frequent induction events. |
| Encoder Resolution | 10,000 to 50,000 PPR | Coarser position feedback, larger potential synchronization errors. | Finer position feedback, greater precision in timing, higher computational load. |
| Induction Window Duration | 50 to 200 ms | Reduced margin for error, requires faster article release mechanisms. | Increased margin for error, allows for slower article release, potential for article misalignment if too wide. |
| Article Weight | 0.1 to 30 kg | Less inertia, faster acceleration/deceleration, easier handling. | Greater inertia, slower response to forces, requires more robust induction mechanisms. |
| Control Unit Scan Time | 1 to 10 ms | Faster system response, more precise timing. | Slower system response, introduces latency in control loops. |
9. Additional Implementations
[0013]This system can be augmented with predictive analytics to anticipate carrier (12) availability and induction station (16) readiness. For example, if a specific induction station (16) frequently experiences articles (18) backing up, the system could dynamically adjust the upstream feed rate to that station (16) or re-route articles (18) to alternative induction points. Furthermore, the carrier (12) could be equipped with individual speed control for its cross belt (14), allowing for optimized article placement and discharge based on article dimensions or fragility. The encoder (20) data could also be used to dynamically adjust the discharge timing of the cross belt (14) at sortation chutes, ensuring articles (18) are ejected squarely into the destination lane regardless of minor speed fluctuations of the main conveyor (10). The system could integrate a vision system at the induction station (16) to measure article (18) dimensions and position on the infeed conveyor, allowing for real-time adjustment of the release point to ensure optimal centering on the carrier (12).
10. Figures
