| 摘要 |
A knife shield comprises a plurality of elongate knives which are arranged side-by-side upon a common support frame, the knives defining a generally cylindrical shield. Each knife is supported on the frame for movement in its longitudinal direction. At least one pair of diametrically opposed knives are coupled together, in the manner of a trackrod, for conjoint movement with respect to the longitudinal axis of the shield. During this movement the knives of the coupled pair concerned remain substantially parallel. The movement of the knives is used for controlling the direction of advance of the shield.
|
