back-up roller

例句：

1. 1. The machine has a back-uproller to prevent jams during operation.
   这台机器有一个备用滚筒，以防止在操作过程中卡住。
2. 2. The construction crew used theback-up roller to remove thedamaged part.
   施工队使用备用滚筒来移除损坏的部分。
3. 3. The engineer tested the machine's back-up roller before startingthe project.
   工程师在开始项目之前测试了机器的备用滚筒。