laravel 5.5 使用whereIn的时候，参数加上变量无法返回结果

我在使用laravel 5.5框架的时候，在使用whereIn中加入获取的变量参数，无法正常返回结果，手动写成数值的时候正常返回。
使用变量：

$ids = '';
        foreach ($menu as $v) {
            if($user[0]['position']==$v['position_id']){
                $ids .= $v['position_id'];
                foreach ($v['child'] as $val) {
                    $ids .= ',' . $val['position_id'];
                }
            }
        }
        $page = $request->page ?: 1;
        $pagesize = $request->pagesize ?: 10;
        $data = $client->leftjoin('industry','client.industry','=','industry.industry_id')
                ->join('client_allot','client.client_id','=','client_allot.client_id')
                ->join('users','client_allot.user_id','=','users.id')
                ->select('client.client_id','company','tacpayer_type',DB::raw('concat(province,city,district) as area'),'industry_name','contact','client.creator','client.created_at')
                ->where('client_type', '=',2)
                ->where('allot_type', '=',1)
                ->whereIn('position',[$ids])
                // ->orderBy(\DB::raw('FIND_IN_SET(position, "' . implode(",", [$ids]) . '"' . ")"))
                ->paginate($pagesize);

使用手动输入参数：

$data = $client->leftjoin('industry','client.industry','=','industry.industry_id')
                ->join('client_allot','client.client_id','=','client_allot.client_id')
                ->join('users','client_allot.user_id','=','users.id')
                ->select('client.client_id','company','tacpayer_type',DB::raw('concat(province,city,district) as area'),'industry_name','contact','client.creator','client.created_at')
                ->where('client_type', '=',2)
                ->where('allot_type', '=',1)
                ->whereIn('position',[4,5,6])
                // ->orderBy(\DB::raw('FIND_IN_SET(position, "' . implode(",", [$ids]) . '"' . ")"))
                ->paginate($pagesize);

![手动输入数值]

我在网上和论坛上找不到任何信息，我自己也检查了几遍，无法找到问题源