| 摘要 |
A support arm has a support structure and an arm structure connected to the support structure through a pivotal connection for pivoting about a horizontal axis. A device is provided for adjusting the elevation of the arm structure by pivoting it about the horizontal axis. A support base is connected to the arm structure through a pivotal connection for pivoting relative to the arm structure about an axis that is parallel to the horizontal axis. A support member is connected to the suppor t base through a pivotal connection for pivoting about a vertical pivot axis, and auxiliary structure such as an air extraction arm may be connected to the support member. A linkage between the support base and the support structure maintains the pivot axis of the support base parallel to a vertical axis as the elevation of the ann structure is adjusted, and avoids the auxiliary structure from swinging under the influence of gravity to a neutral position different from that desired by an operator. |
