lidar is detecting pillars of robots as obstacles in local map.how to set minimum range of scan sensor or any other method to solve this problem

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Are you talking about a local cost map? If you are using the obstacles layer, there is a footprint_clearing_enabled parameter, which defaults to true. Make sure it is not set accidentally set to false. If it's still not clearing, ensure that your footprint is properly defined. This is also important for avoiding obstacles in general.

That said, the laser_filters package (as Procópio suggested) is probably also useful as it will remove the pillars from the data stream completely. This will likely improve the quality of SLAM and other applications of your lidar data.