company news about Servo Traversing vs. Mechanical Traversing: A Technical Comparison of Tension Control in PP Strapping Winding Machines

Introduction

In the strapping winding process, the choice of traversing system directly determines finished roll quality, production efficiency, and scrap rate. Two mainstream technologies dominate the market today — mechanical traversing and servo traversing — which differ significantly in tension control accuracy, applicable speed range, and total cost of ownership. This article provides a systematic comparison from three perspectives: working principles, measured test data, and application scenarios, to support your equipment selection with professional insights.

1. Working Principle Comparison

1.1 Mechanical Traversing: Traditional Cam / Leadscrew Drive

Mechanical traversing is the oldest method used in strapping winders. Its core components are a mechanical cam or reciprocating leadscrew. As the winding shaft rotates, power is transmitted via gears or chains to rotate the cam, which pushes the traversing guide roller to move back and forth along the axial direction, thereby arranging the strapping in layers on the paper core.

Technical characteristics:

• Drive method: Purely mechanical gear/chain transmission, no electrical feedback

• Traversing profile: Fixed by cam contour or leadscrew pitch, not adjustable

• Tension control: Relies on a torque motor (open-loop), unable to respond to real‑time tension variations

• Reversal control: Mechanical limit switches trigger reversal, with inherent response delay

1.2 Servo Traversing: Closed‑Loop Servo Drive

Servo traversing uses an independent servo motor to drive the traversing mechanism, with the PLC control system synchronising the traversing motion with the main winding spindle. The servo traversing system operates with the winding servo as the master axis and the traversing servo as the slave axis, strictly following the motion curve programmed in the control system.

Technical characteristics:

• Drive method: Servo motor direct drive or via precision gear reducer

• Traversing profile: Programmable – width and pitch freely settable

• Tension control: Real‑time feedback from tension sensor; servo motor responds in milliseconds

• Reversal control: Intelligent reversal based on real‑time roll diameter calculation and position feedback

1.3 Summary of Operating Principle Differences

2. Measured Tension Fluctuation Data Comparison

To verify the tension control accuracy of both traversing systems, the technical team at Jiaxing Chuanqi conducted comparative tests under identical conditions.

2.1 Test Conditions

• Test equipment: CQ Series fully automatic drop‑down winders (servo traversing model vs. mechanical traversing model)

• Test material: PP strapping, width 12mm, thickness 0.6mm

• Test speeds: 50 m/min, 100 m/min, 150 m/min, 200 m/min, 250 m/min

• Measurement instrument: Digital tension meter (accuracy ±0.01 N)

• Sampling frequency: 10 readings per second, 60 seconds of continuous sampling at each speed

• Test environment: Temperature 25±2°C, humidity 60±5%

2.2 Measured Data

2.3 Data Interpretation

Low‑speed range (50‑100 m/min): Both systems show relatively small tension fluctuations; mechanical traversing can meet basic needs. However, at 100 m/min the fluctuation reaches ±0.62 N, which begins to visibly affect roll neatness.

Medium‑speed range (150‑200 m/min): Mechanical traversing fluctuations increase sharply (from ±0.85 N to ±1.18 N), with obvious “bell‑mouth” and “bamboo‑node” defects observed on finished rolls. Servo traversing fluctuations only rise slightly from ±0.13 N to ±0.17 N, maintaining excellent roll shape.

High‑speed range (250 m/min): Mechanical traversing fluctuations reach ±1.52 N, failing to guarantee acceptable winding quality; servo traversing remains at an excellent ±0.21 N.

Fluctuation improvement: Servo traversing consistently delivers over 82% improvement across all speeds, peaking at 86% at 200‑250 m/min.

3. Why Does Servo Traversing Provide More Accurate Tension Control?

3.1 Closed‑Loop vs. Open‑Loop Control

Mechanical traversing uses open‑loop control: the control system issues a command but does not verify the result. The torque motor delivers a preset torque, but it cannot sense actual changes in strapping tension. When line speed fluctuates, when raw material batches change, or when paper core roundness deviates, mechanical traversing cannot compensate.

Servo traversing, by contrast, employs full closed‑loop control. A tension sensor continuously measures the actual strapping tension and feeds the signal back to the PLC. The PLC compares the measured value with the setpoint; whenever a deviation occurs, it immediately sends a correction command to the servo motor, which adjusts torque or speed within milliseconds to bring tension back to the target range. This cycle repeats continuously, achieving dynamic tension constancy.

3.2 Traversing Precision Comparison

For mechanical traversing, the traversing width is determined by the cam profile or leadscrew pitch – fixed and single‑value. Changing paper core width or strapping width requires manually changing change gears or adjusting mechanical parts – a cumbersome process with poor accuracy.

For servo traversing, the traversing width, pitch, and reversal points are all set on the touch screen – fully programmable. When changing specifications, the operator simply recalls the corresponding recipe; traversing accuracy is unaffected by mechanical wear.

3.3 Reversal Response Comparison

Mechanical traversing relies on mechanical limit switches to trigger reversal, introducing physical contact delay and positioning error. As speed increases, this delay is amplified, causing reversal points to shift, resulting in “overlap” or “gaps” at the roll edges.

Servo traversing performs intelligent reversal based on real‑time roll diameter calculation and position feedback, with no physical contact delay. Reversal point accuracy can be controlled within ±0.5 mm.

4. Applicable Speed Range and Selection Recommendations

4.1 Recommended Traversing Type by Speed Range

4.2 Selection Decision Guidelines

If your line speed is ≤120 m/min: Mechanical traversing can meet basic requirements. However, be aware that as the equipment ages, mechanical wear will progressively reduce accuracy, leading to increasing maintenance costs over time.

If your line speed is 120‑180 m/min: Servo traversing is strongly recommended. Measured data show that in this speed range, mechanical traversing already causes a noticeable increase in scrap rate, while servo traversing continues to deliver stable performance. Although the initial investment is higher, based on an annual output of 2,000 tonnes, servo traversing can reduce scrap by approximately 60‑80 tonnes per year.

If your line speed is ≥180 m/min: Servo traversing is the only viable choice. Mechanical traversing cannot maintain stable winding quality at these speeds.

5. Q&A Section

Q1: How much higher is the initial investment for servo traversing compared to mechanical traversing? What is the payback period?

A: Servo traversing typically costs 30‑50% more upfront than mechanical traversing, mainly due to the servo motor, driver, tension sensor, and control system. However, based on an annual output of 3,000 tonnes and a 6‑percentage‑point reduction in scrap rate, the annual scrap saving amounts to about 90 tonnes. At a market price of approximately US$1,300 per tonne, this translates to roughly US$117,000 in annual savings. The payback period is typically 6‑12 months.

Q2: How difficult and costly is the maintenance of a servo traversing system?

Pub Time : 2026-06-24 09:26:59 >> News list