A sonic generator produces a reciprocating force that is transmitted to a tool by a resonant or nonresonant force transmitting member having an output that reciprocates about a neutral position responsive to the force of the sonic generator. A continuous unidirectional force is applied to the sonic generator by a tool carrier. The tool advances intermittently along a work path through a medium responsive to the continuous unidirectional force and the reciprocating force. A gap is held between the neutral output position of the transmitting member and the tool when the tool is unable to advance through the medium responsive to the continuous unidirectional force and the reciprocating force. Specifically, the force of the sonic generator is sufficiently large relative to the unidirectional force to overcome the latter, and to drive the tool holder back away from the tool when the tool is unable to advance along the work path, thereby establishing a protective gap. When the force transmitting member is resonant, cessation of resonance is prevented when the tool encounters an immovable object by establishing the protective gap in the described manner.

A sonic generator produces a reciprocating force that is transmitted to a tool by a resonant or nonresonant force transmitting member having an output that reciprocates about a neutral position responsive to the force of the sonic generator. A continuous unidirectional force is applied to the sonic generator by a tool carrier. The tool advances intermittently along a work path through a medium responsive to the continuous unidirectional force and the reciprocating force. A gap is held between the neutral output position of the transmitting member and the tool when the tool is unable to advance through the medium responsive to the continuous unidirectional force and the reciprocating force. Specifically, the force of the sonic generator is sufficiently large relative to the unidirectional force to overcome the latter, and to drive the tool holder back away from the tool when the tool is unable to advance along the work path, thereby establishing a protective gap. When the force transmitting member is resonant, cessation of resonance is prevented when the tool encounters an immovable object by establishing the protective gap in the described manner.

A sonic generator produces a reciprocating force that is transmitted to a tool by a resonant or nonresonant force transmitting member having an output that reciprocates in forward and backward directions about a neutral position responsive to the force of the sonic generator. The tool is located forward of the output of the force transmitting member, and is movable in backward and forward directions along the work path. A changing gap is formed between the tool and the output as the output reciprocates, the gap tending to close and strike the tool as the output reciprocates in a forward direction and tending to open as the output reciprocates in a backward direction. A continuous unidirectional force is applied to the force transmitting member. The tool advances intermittently along the work path through the material being processed responsive to the continuous unidirectional force and the reciprocating force. A protective gap is maintained by a tool stop between the tool and the output of the force transmitting member. The width of the tool stop is precisely controlled by shimming the tool stop and/or the supports for the force transmitting member.

A ripping tool positioned below the earth's surface is driven by the output of a vibrating, preferably, resonant, force transmitting beam which has lateral dimensions smaller than those of the ripping tool and is positioned below the earth's surface. The beam is configured to have a single resonant node when restrained from vibrating at such node and is supported so that the single node is above the earth's surface and restrained from vibrating. The output of the beam is enlarged in thickness to form a hammer.

A harrow comprises an elongate tool bar formed in three sections including a central section and two wing sections all of which can rotate about a longitudinal axis, The wing sections are coupled by pivot couplings which allow the wing sections to fold rearwardly in the transport position. The tool bar carries a number of harrow elements each of which is formed by a rigid frame defined by longitudinal rails and welded cross bars with the frame carrying a plurality of tine support bars. A push rod simultaneously rotates all of the tine support bars about their respective axis to vary the angle of the tine in contact with the ground. The angle of the tines of all of the harrow elements are adjusted simultaneously by a number of rocker shafts mounted on the tool bar and operated by rephasing cylinders. Each push bar of each harrow element is attached to the respective rocker shaft for actuation. The harrow frame is mounted on a bracket passing underneath the square section tool bar and pivots about a horizontal axis just rearward of the tool bar with tension springs forwardly of the tool bar pulling the frame upwardly. The tool bar can be rotated beyond the horizontal position to apply downward pressure on the harrow frame against the ground.