Zigzag stacking is a method of building up single electrode sheets in prismatic battery assembly. Samsung SDI is converting from winding to zigzag stacking starting with its gen5 prismatic battery, scheduled for production in the second half of this year.
Problem Definition
The winding method is a continuous process, so alignment error does not accumulate, but it has low space-utilization inside a prismatic can. Zigzag stacking increases space utilization but requires sheet-by-sheet alignment every cycle. Increasing alignment speed increases the inertial force of stack-base motion, and when inertial force exceeds vacuum-suction force, the electrode sheet drops. This article asks whether a trajectory-design criterion is needed that simultaneously satisfies cycle-time reduction and suction stability.
Kinematic Analysis
The stack base receives a single electrode sheet from the vacuum belt conveyor and moves it along a U-shaped or semicircular trajectory. This trajectory shape is intended to direct the acceleration direction upward so that the stack gripper applies force to the broad face of the separator. The smaller the trajectory radius, the shorter the cycle time, but centripetal acceleration increases in proportion to the radius. The calculation below is a methodology example; the actual specifications should be confirmed after field measurement.
Calculation / Formula Verification
At a target cycle time of $t = 0.3\text{ s}$ and travel angle $\theta = \pi\text{ rad}$ (semicircular trajectory), angular velocity is $$\omega = \frac{\theta}{t} = \frac{\pi}{0.3} \approx 10.47\text{ rad/s}$$
At a trajectory radius of $r = 60\text{ mm} = 0.06\text{ m}$ (estimated; example based on equipment-width constraint), centripetal acceleration is $$a = \omega^2 r = (10.47)^2 \times 0.06 \approx 6.58\text{ m/s}^2$$
At an electrode-sheet mass of $m = 3.2\text{ g} = 0.0032\text{ kg}$ (estimated; based on similar specifications for a single 46-phi-compatible prismatic electrode sheet), the inertial force is $$F = ma \approx 0.0211\text{ N}$$ This inertial force is the minimum load the suction pad must withstand, and it grows larger as the trajectory radius is reduced.
Applying a suction-pad diameter of φ8mm and vacuum pressure $\Delta P = 60\text{ kPa}$ (estimated), the effective area is $A = \pi(4\text{mm})^2 \approx 50.3\times10^{-6}\text{ m}^2$, giving a suction force of $$F_{vac} = \Delta P \times A \approx 3.02\text{ N}$$
The primary safety factor is $SF_1 = F_{vac}/F \approx 143$. Under normal conditions, suction force overwhelmingly exceeds inertial force, and counter to intuition, the high-speed trajectory itself is not the main cause of drop risk. As a secondary check, assuming vacuum pressure degrades by 50% due to filter contamination or similar, $F_{vac}’ \approx 1.51\text{ N}$, $SF_2 \approx 71.5$. Even under the degraded condition, the safety factor remains sufficient, leading to the conclusion that the real bottleneck lies in the balance between sheet-alignment repeatability precision and cycle time.
Shop-notes
A mechanical clamp gripper was reviewed as an alternative but not adopted, due to the risk of edge-burr damage to the electrode sheet and concern over reduced repeatable-alignment precision. Vacuum-pad hole machining requires micro-drilling to a tolerance of ±0.02mm, which has good machinability, but the added assembly effort for inserting a porous filter must be reflected in the assembly-line takt time. The actual safety-management focal point is not trajectory acceleration but the placement of line sensors to detect vacuum-pressure drops.
Design-Reflection Checklist
- Re-calculate centripetal acceleration based on stack-base trajectory radius and target cycle time
- Dual safety-factor verification including a 50% vacuum-pressure-degradation scenario
- Prepare a comparison table of sheet-alignment tolerance vs. can-interior clearance
- Standardize vacuum-pad hole machining tolerance and filter replacement interval
- All estimated values above should be fully reconfirmed with field-measured values
One-line summary: The drop risk in zigzag stacking is determined not by trajectory acceleration but by the vacuum-pressure-degradation monitoring system.