diff --git a/public/fourbar_test.html b/public/fourbar_test.html
index ffd7866..6fc9b2e 100644
--- a/public/fourbar_test.html
+++ b/public/fourbar_test.html
@@ -841,6 +841,7 @@
       let scanAnimation = {
         active: false,
         frame: 0,
+        direction: 1,
         timer: 0,
         intervalId: null,
       };
@@ -1318,18 +1319,30 @@
       function animateScanFrame() {
         const validRows = latestScan.filter((row) => row.ok);
         if (!validRows.length) {
-          pauseScanAnimation();
+          stopScanAnimation();
           return;
         }
 
-        const row = validRows[scanAnimation.frame % validRows.length];
+        const clampedFrame = Math.max(0, Math.min(scanAnimation.frame, validRows.length - 1));
+        const row = validRows[clampedFrame];
         const input = { ...readInput(), startValue: row.inputValue };
         renderThreeMechanism(
           row.points,
           input,
           { title: "扫描播放中", value: row.inputValue },
         );
-        scanAnimation.frame += 1;
+
+        if (validRows.length <= 1) {
+          scanAnimation.frame = 0;
+          return;
+        }
+
+        if (clampedFrame >= validRows.length - 1) {
+          scanAnimation.direction = -1;
+        } else if (clampedFrame <= 0) {
+          scanAnimation.direction = 1;
+        }
+        scanAnimation.frame = clampedFrame + scanAnimation.direction;
       }
 
       // 开始播放已扫描的接口点位。
@@ -1345,19 +1358,27 @@
         }
         scanAnimation.active = true;
         scanAnimation.timer = 0;
+        scanAnimation.direction = scanAnimation.direction || 1;
         animateScanFrame();
         scanAnimation.intervalId = window.setInterval(animateScanFrame, 120);
         setMessage("正在播放扫描点位动画", "is-ok");
       }
 
-      // 暂停 3D 扫描动画。
-      function pauseScanAnimation() {
+      // 停止 3D 扫描动画，可选择是否刷新提示文案。
+      function stopScanAnimation(options = {}) {
         scanAnimation.active = false;
         if (scanAnimation.intervalId) {
           clearInterval(scanAnimation.intervalId);
           scanAnimation.intervalId = null;
         }
-        setMessage("3D 动画已暂停", "is-ok");
+        if (options.showMessage) {
+          setMessage("3D 动画已暂停", "is-ok");
+        }
+      }
+
+      // 暂停 3D 扫描动画。
+      function pauseScanAnimation() {
+        stopScanAnimation({ showMessage: true });
       }
 
       // 加载并初始化 WASM 模块。
@@ -1588,7 +1609,7 @@
           true,
         );
 
-        renderThreeMechanism(points, input, { fitCamera: true, value: frame.inputValue ?? input.startValue });
+        renderThreeMechanism(points, input, { value: frame.inputValue ?? input.startValue });
       }
 
       // 渲染仿真扫描汇总图。
@@ -1654,6 +1675,7 @@
       // 执行当前角度的单次接口验证。
       async function runOnce() {
         try {
+          stopScanAnimation();
           setMessage("");
           requestStatus.textContent = "执行中";
           requestStatus.className = "badge warn";
@@ -1670,11 +1692,9 @@
           renderSummary(response, input);
           renderChecks(response, input);
           if (response.res_data && response.res_data.success) {
-            scanAnimation.active = false;
             renderMechanismChart(response, input);
             setMessage("接口调用完成，当前姿态已刷新", "is-ok");
           } else {
-            scanAnimation.active = false;
             setMessage(response.res_data?.error || response.msg || "接口返回业务失败", "is-error");
           }
           requestStatus.textContent = "已执行";
@@ -1691,6 +1711,7 @@
       // 调用批量仿真接口，生成轨迹和位移曲线。
       async function runScan() {
         try {
+          stopScanAnimation();
           setMessage("");
           const baseInput = readInput();
           const stepTime = Number(stepInput.value);
@@ -1736,6 +1757,7 @@
           scanOutput.textContent = JSON.stringify(response, null, 2);
           renderScanCharts(rows);
           scanAnimation.frame = 0;
+          scanAnimation.direction = 1;
           requestStatus.textContent = "扫描完成";
           requestStatus.className = "badge ok";
           renderSummary(response, baseInput);