The precision fixed-length cutting relies on a “pre-signal + precise positioning” mechanism, which ensures the cut length of profiles matches the target dimension exactly. Here’s the detailed principle:
1. “Buffer Reservation” Design: Distance Between Limit Switch and Cutting Blade
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Fixed-length dimension: The target length of the profile after cutting (e.g., 1000mm if the profile is to be cut into 1000mm length).
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Role of the limit switch: It acts as a “pre-signal detector” rather than directly controlling the cut. When the profile approaches the cutting position, the switch is triggered to send a signal to the control system, serving as an advance notice: “The profile is approaching the cutting position—prepare for positioning!”
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Why the distance must be shorter than the fixed length:
Suppose the fixed length is 1000mm, and the distance between the limit switch and the cutting blade is set to 800mm (shorter than 1000mm). As the profile exits the roll forming machine and moves along the guide rail, its front end (or a specific positioning mark) triggers the limit switch when it has traveled 800mm. This signal activates the subsequent “positioning cylinder” operation, leaving a 200mm buffer for precise alignment to the cutting position. -
Problems with improper distances:
- If equal to 1000mm: The profile reaches the theoretical cutting position when triggering the switch, leaving no buffer for the positioning cylinder to adjust, causing cutting deviations.
- If longer than 1000mm: The switch is triggered prematurely, leading to early positioning and cutting, resulting in profiles shorter than the fixed length.
Thus, a shorter distance ensures sufficient time for precise positioning, avoiding errors from signal delays or mechanical inertia.
2. Core Positioning Logic: Positioning Cylinder Controls Critical Distance
This step eliminates errors through mechanical positioning, relying on two key components:
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Positioning hole: A preset mark on the profile (e.g., a small hole punched during roll forming) or a fixed reference point on the machine. It serves as the length benchmark—the final cut length equals the distance from this hole to the cutting blade (e.g., if the designed distance from the hole to the profile end is 1000mm, aligning the blade 1000mm from the hole guarantees precision).
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Role of the positioning cylinder: As the “mechanical positioning actuator,” it fixes the profile’s position via piston rod extension/retraction (extending to press against the profile or its positioning structure, retracting to release), ensuring the distance from the positioning hole to the blade strictly matches the fixed length.
3. Execution Process
- The profile triggers the limit switch after traveling 800mm, sending a signal to the control system.
- The system activates the positioning cylinder: Its piston rod extends to engage the positioning hole (or a matching pin), forcing the profile to stop. If there’s a feeding error (e.g., the profile travels 805mm due to uneven feeding), the cylinder mechanically adjusts the position (pulling back or holding) to ensure the distance from the positioning hole to the blade is exactly 1000mm.
- Once positioned, the control system activates the cutting blade (e.g., hydraulically driven) to cut the profile, resulting in a precise 1000mm length.
Summary
The “buffer reservation” (via the limit switch) provides advance warning and adjustment time, while the positioning cylinder eliminates feeding errors through mechanical force. Together, they replace “estimated positioning” with mechanical precision, ensuring the cut length matches the fixed dimension exactly—avoiding cumulative errors from speed-controlled cutting alone.