Introduction: The logistics industry has recently been designated as one of the ten key industries for national revitalization, and automated warehouses play a crucial role in the entire logistics chain. Modern laser ranging and positioning technology is vital in automated warehouses. Its application in the automatic control system of rail-guided stacker cranes has enabled absolute positioning of the cranes. This not only effectively solves the problems of accuracy and reliability in counting and positioning but also facilitates smooth speed adjustment, thereby improving the overall performance of the stacker crane.
As the level of automation in the logistics sector increases, various information technologies such as optoelectronic technology, computer technology, and control technology are widely used. Among them, laser detection technology, with its advantages in ranging and positioning, plays a key role in equipment such as laser stacker cranes and automatic guide machines, and actively promotes the improvement of the overall performance of the logistics system.
Especially in the automatic control system of rail-guided stacker cranes, the application of technologies such as laser ranging and positioning, PLC control, distributed fieldbus, and vector frequency conversion speed regulation has enabled the control system to surpass the original design concept. It achieves absolute addressing of the stacker crane, effectively solving the problems of accuracy and reliability in counting and positioning, and conveniently realizing smooth speed regulation, optimizing speed curves, and improving starting and braking performance. This improves the overall performance of the stacker crane, ensuring reliable, stable, and efficient operation. Currently, this technology is widely used in machinery, food, tobacco, electronics, automotive, distribution centers, pharmaceuticals, electrical appliances, and warehousing industries.
System composition and hardware configuration:
Automated storage and retrieval systems (AS/RS) are comprehensive engineering projects involving multiple disciplines such as civil engineering, mechanical engineering, electrical engineering, communications, and information technology. Mechanical equipment includes racking systems, handling machinery, conveyor systems, distribution trolleys, inbound and outbound platforms, and containers and pallets. Electrical equipment includes control devices, drive systems, frequency converters, control panels, PLC control modules, detection devices, communication equipment, monitoring and dispatching equipment, computer management equipment, and screen display and image monitoring equipment. The computer system mainly comprises monitoring systems, management systems, database servers, communication systems, and computer network control.
To enhance the overall performance of stacker cranes, Banner Engineering introduced the LT7 long-range laser sensor, a high-precision, ultra-long-range "Time-of-Flight" laser distance sensor with a detection range of up to 250 meters. Its main features are as follows:
Optional reflector type, 2 PNP outputs, detection distance up to 250m;
Select direct-reflection type, 2 PNP outputs, 4-20mA analog output, background suppression, detection distance up to 10m;
It provides two alarm outputs, along with an LCD display, making fault analysis easy;
Key instruction can be completed via buttons or a serial interface;
Continuous detection distance display;
10 mm linearity;
RS-422 and SSI connectors are optional;
Uses a visual level 2 laser for precise alignment;
Rapid preheating minimizes drift.
Automated storage and retrieval systems (AS/RS) are comprehensive projects involving multiple disciplines such as civil engineering, mechanical engineering, electrical engineering, communications, and information technology. They mainly consist of four categories of equipment: civil engineering equipment, mechanical equipment, electrical equipment, and computer systems. Mechanical equipment includes racking systems, handling machinery, conveyor systems, distribution trolleys, inbound and outbound platforms, and pallets and containers. Electrical equipment includes electrical control devices, drive systems, frequency converters, control panels, PLC control modules, detection devices, communication equipment, and monitoring systems.
Control and dispatching equipment, computer management equipment, and screen display image monitoring equipment; the computer system mainly includes monitoring system, management system, database server, communication system, computer network control and other components.
1. AS and RS system configuration
Automated storage and retrieval systems (AS/RS) consist of racking, stacker cranes, cargo boxes, floor rails, inbound and outbound platforms, conveyors, laser measuring instruments, communication equipment, and monitoring equipment, as shown in Figure 1. Its main workflow is as follows:
Inbound operation process: Receive inbound operation command → Inbound/outbound station → Pick up box → Stacker crane → Automated warehouse rack → Storage box → Return to inbound/outbound station → Inbound operation completed (standby):
Outbound operation process: Receive outbound operation command → Go to destination address → Automated warehouse rack → Picking box → Stacker crane → Inbound/outbound station → Storage box → Conveyor → Inbound/outbound station → Complete outbound and return to inbound station for standby.
Figure 1 shows an automated storage and retrieval system (AS/RS) with one aisle. Typically, an AS/RS consists of multiple aisles. The aisle-mounted stacker crane is the core equipment and main handling device of the AS/RS. Its main purpose is to shuttle back and forth within the aisles of the high-rise racking system, automatically storing and retrieving goods located at the aisle entrance and placing them into designated storage locations (inbound operations), or retrieving goods from storage locations and transporting them to the aisle entrance (outbound operations), or moving goods from one storage location to another (inventory and transfer operations). AS/RS is widely used in supply chain logistics, precision warehousing, and rapid delivery.
The overall structure and main electrical component layout of the stacker crane are shown in Figure 2.
2. Stacker crane electrical control system bus network structure
The entire automated storage and retrieval system (AS/RS) uses a Profibus-DP network for data communication. PLC programmable controllers, laser rangefinders, horizontal movement inverters, vertical movement inverters, forklift movement inverters, control panel touchscreens, and supervisory control systems are connected to the Profibus-DP network, forming a unified Profibus-DP network. Each component connected to the DP network is assigned a unique DP bus address. Access to different DP bus addresses enables communication between components.
It also processes the data to achieve automatic positioning, ranging, and speed control of the stacking equipment.
1. Implementation of laser ranging and positioning
(1) Initialization and self-learning of basic data for storage locations
During the PLC's power-on initialization and self-test, the absolute address data of the inbound/outbound platform and each storage compartment is read out using a laser rangefinder. This data is automatically saved to the PLC's internal storage location address data table DB0. Modifications and saves are then performed to the storage location address data table DB0 for use by the stacker crane for positioning, completing the initialization and calibration of the original data.
(2) Stacker crane operation data processing
When the stacker crane receives a work instruction from the host computer or the touch screen on the control panel, the PLC programmable controller accepts the work instruction, loads the target pointer according to the work instruction, modifies the target pointer to point to the corresponding position in the storage location address data table DB0, and reads out the data corresponding to the target pointer as the current work destination address LN; at the same time, it reads the current address ID0 of the stacker crane through the laser rangefinder and stores it in the PLC for program calculation.
(3) Implementation of laser ranging and positioning
The PLC program processes the above data to achieve stacker crane address recognition and positioning. Because laser ranging enables absolute address recognition and digitizes the storage location settings, it facilitates the setting of storage location data, inbound/outbound platform positions, and operating speed values, making it easy to achieve functions such as data comparison, counting, automatic speed changing, and precise positioning.
2. Implementation of smooth speed regulation for stacker cranes
After acquiring dynamic operating data through the PLC, the displacement difference ΔL between the current column address ID0 and the destination column address LN can be calculated using the formula ΔL = LN - ID0. Since the stacker crane's calculation speed is derived from the displacement difference, the calculation speed changes continuously with the change in displacement difference. This allows for continuous control of the stacker crane's operating speed, and automatic speed switching via the program, thus achieving smooth speed regulation of the stacker crane.
Typically, the maximum operating speed of a stacker crane is limited by factors such as the stacker crane mechanism, motor performance, power, load, and safety, and is subject to a maximum speed limit. The minimum operating speed of a stacker crane is affected by factors such as load and driving torque, and is subject to a minimum speed limit; otherwise, it cannot be driven or work normally at low speeds.
By applying laser ranging and positioning technology to stacker crane systems in aisle tunnels, absolute addressing technology for stacker cranes has been achieved. Compared to traditional relative addressing technology using detection pads, this not only effectively improves detection speed and efficiency but also effectively solves the problems of accuracy and reliability in counting and positioning. Furthermore, it digitizes ranging, addressing, and speed regulation, making it easier to implement changes to warehouse and cargo location addresses, optimize speed curves, and improve starting and braking performance. This significantly enhances the overall performance of the stacker crane, ensuring key parameters such as positioning accuracy, operational stability, and noise levels.
