A cart-borne ultrasonic imaging system has a cart housing; a control panel or a support for a portable ultrasound unit; and an articulating arm assembly to which the control panel, or the support is connected. The articulating arm assembly has arms pivotally connected with a first joint rotatably mounted on the cart and a second joint rotatably mounted on the control panel, or the support. At least one of the arms includes a 4-bar linkage,

A locking mechanism restricts motion of the articulating arm assembly and comprises electromagnetic elements controllable to exert magnetic force on movable actuating elements. The moveable actuating elements have a friction mass with corresponding braking element to restrict rotation of the first joint and/or of the second joint and/or a locking member kinematically coupled with main damping member to restrict its movement and that of the 4-bar linkage.