Problem Definition
Winding is the assembly process that overlaps and winds electrode and separator to form a jelly roll. Published patent EP4117067A1 (family: US2022363502A1, CN113241480B, priority CN202110509137, filed May 11, 2021) discloses a winding machine that winds the separator at continuous constant speed without stopping. The applicant name is not disclosed within this search scope, and the priority filing is confirmed to be of Chinese nationality. The patent’s core claim is that if the separator does not pass through the winding needle’s center during winding-head replacement, there is no need to decelerate separator speed during cell changeover after cutting. Compared with the existing winding-needle method that fixes the separator with a center clamp pin, can this structure actually achieve changeover without speed loss?
Kinematic Analysis
The winding mechanism of this patent consists of a base plate, an electrode-feed mechanism, a winding mechanism, a separator-cutting mechanism, and a separator-splicing mechanism. The winding mechanism includes three winding needles rotatably mounted on the winding head. The needle at the winding position suction-adheres the cut end of the separator and winds it around the needle’s outer circumferential surface, in a structure where the separator does not pass through the needle’s center. This method enables a simple needle structure without a center clamp pin, and the specification states that cell changeover is possible without separator speed loss.
Calculation / Formula Verification
Winding tension is managed as a safety factor against separator tensile strength. The relationship between winding tension $T$ (N), the friction coefficient $\mu$ on the needle’s outer circumferential surface, and the wrap angle $\theta$ (rad) can be approximated in the belt-friction equation form $T_{in} = T_{out} \cdot e^{\mu\theta}$. If $\mu$ of the suction-type needle surface is low, initial-wrap slip occurs and separator position shifts, so suction pressure and needle surface-roughness specifications must be managed together. To maintain constant-speed winding, the fluctuation range of separator feed tension must stay within the target tension’s allowable range; this fluctuation criterion varies with material properties and should be confirmed after field measurement.
Separator tensile safety factor is verified doubly. The static tensile safety factor $SF_{tension} = F_{break} / T_{max} \geq 2$ must be satisfied, and, separately, the fatigue safety factor $SF_{flex}$ from repeated flexing must also be confirmed, with both conditions required to be met.
Shop-notes
- An alternative mechanism of decelerating-cutting-reaccelerating while retaining the center clamp pin could be considered, but this induces winding-speed variation between cells and lowers production UPH, so it is recorded as a not-adopted reason.
- Machinability note: when machining the vacuum holes on the suction-type needle’s outer circumferential surface, tighter hole-spacing lowers needle stiffness, so the trade-off between vacuum-hole machining pattern and needle shaft stiffness must be separately reviewed.
Design-Reflection Checklist
- Confirm needle outer-surface friction coefficient and suction-pressure specifications
- Measure separator tension fluctuation range and verify by substituting into the belt-friction equation
- Calculate static and fatigue tensile safety factors doubly
- Re-analyze needle stiffness for each vacuum-hole machining pattern
One-Line Summary
EP4117067A1’s needle outer-surface suction-type winding structure enables constant-speed cell changeover, but the trade-off between vacuum-hole machining and needle stiffness requires separate analysis.