Forklift Mast Lift Sequence Detection for Hydraulic Stroke Control
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Solution Overview
Problem
Industrial trucks face issues with stroke sequence errors during the free lift and mast lift operations, leading to incorrect extension of the mast lift before the free stroke is complete, due to differences in hydraulic pressure requirements and longer supply lines for the free stroke stage.
Innovation Solution
A forklift truck with a common hydraulic circuit for the free lift and mast lift cylinders, equipped with a stroke sequence detection device that monitors the lift sequence, limits the lifting speed based on a characteristic map, and uses proximity switches and pressure sensors to ensure the correct sequence by adjusting the lifting speed and height detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the free stroke cylinder has significantly longer supply lines than the mast stroke cylinder, then the free stroke stage can be designed with proper hydraulic supply, but stroke sequence errors occur where the mast stroke extends before the free stroke is complete
Solution Approach 1:
The patent employs a stroke sequence detection device that monitors the extension status of both the free stroke cylinder and mast stroke cylinder. This feedback mechanism detects whether the free stroke has reached its end position before allowing the mast stroke to extend, preventing sequence errors. The detection device provides real-time information about cylinder positions to the control system, enabling corrective action if improper sequencing is detected.
Solution Approach 2:
The system performs preliminary detection of the free stroke completion status before initiating the mast stroke extension. The stroke sequence detection device checks whether the free stroke cylinder has reached its end position in advance, and only then permits the mast stroke cylinder to extend. This preliminary verification prevents the harmful condition of mast extension before free stroke completion.
2Stress or pressure
If the surface area ratios of hydraulic cylinders are designed for lower pressure in free lift, then the free stroke occurs first as intended, but stroke sequence errors occur when hydraulic pressure causes mast lift to extend prematurely
Solution Approach 1:
The stroke sequence detection device continuously monitors the actual extension status of both cylinders and provides feedback to the control system. When premature mast extension is detected despite the pressure differential design, the system can intervene to correct the sequencing error, ensuring reliable operation despite the inherent pressure-based control approach.
Solution Approach 2:
The patent introduces a stroke sequence detection device as an intermediary between the hydraulic pressure system and the cylinder extension action. This intermediary monitors and verifies the proper sequencing before allowing mast stroke extension, acting as a safeguard against premature extension caused by hydraulic pressure variations.
3Productivity
If the lifting speed of the free lift stage is increased to improve productivity, then material handling efficiency improves, but stroke sequence errors occur when the mast stroke extends before the free stroke is complete
Solution Approach 1:
The stroke sequence detection device provides real-time feedback on the extension status of both cylinders, enabling the control system to maintain high lifting speeds while preventing sequence errors. The feedback mechanism ensures that even at high speeds, the system can detect and prevent premature mast extension, maintaining both productivity and reliability.
Solution Approach 2:
The detection device performs preliminary verification of free stroke completion status before permitting mast stroke extension, even during high-speed operation. This preliminary check occurs rapidly and automatically, allowing the system to maintain high productivity while ensuring proper sequencing through advance verification.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Prevents stroke sequence errors by ensuring the mast lift stage extends only after the free lift stage has reached its end, maintaining a flawless lifting operation and enhancing safety and efficiency.
Implementation Method 1
a common hydraulic circuit is provided for the at least one free lift cylinder and for the at least one mast lift cylinder
Implementation Method 2
a lift sequence detection device is provided to detect a lift sequence when the at least one free lift cylinder and/or when the at least one mast lift cylinder is actuated
Data Source
Figure 1
Figure 2a~2b
Figure 3
AI summary
The invention relates, among other things, to a forklift truck (2) with a lifting mast (4) which is designed with a free lifting stage driven by at least one free lifting cylinder (8) and with at least one or more mast lifting stages driven by at least one mast lifting cylinder (12), wherein a load handling device (6) is movable along the lifting mast (4), preferably in a vertical direction, by means of the free lifting stage and/or by means of the at least one mast lifting stage, wherein a common hydraulic circuit is provided for the at least one free lifting cylinder (8) and for the at least one mast lifting cylinder (12), wherein a lifting sequence detection device is provided to detect a lifting sequence when the at least one free lifting cylinder (8) and/or when the at least one mast lifting cylinder (12) is actuated.