The helical rotary actuator is composed of a tubular housing and only two moving parts: a central through shaft and an annular piston sleeve. As hydraulic pressure is applied, straight gears on the piston OD force the piston's axial displacement in the housing, while helical gears on the shaft and piston ID force the shaft to rotate and open the jaw.
Buckets with cylinder-actuated moving jaws have been used on front-end wheeled loaders and backhoes for many years. This same articulating jaw concept has also been used for excavator buckets more recently. The jaw feature increases the versatility and productivity of excavators; in essence, a single bucket offers the functionality of several attachments. Without changing buckets, the jaw bucket can be used as a hydraulic thumb, a general excavating bucket with teeth, a smoothed lip grading bucket, or as a grapple for handling material.
Helac Corp., Enumclaw, Wash., has developed an improved jaw bucket design, marketed as the PowerGrip Multi-Purpose Bucket. Instead of relying on cylinders and brackets, Helac has achieved 120° of jaw movement by integrating a helical hydraulic rotary actuator into the bucket shell.
The rotary actuator design gives the PowerGrip a number of advantages over cylinder style jaw buckets:
The PowerGrip is available in several sizes, widths, and configurations for backhoes and excavators between 12,000 and 45,000 lb.
PowerGrip uses Helac's helical-hydraulic rotary actuator technology to operate the jaw. The rotary actuator is composed of a tubular housing with integral ring gear and only two moving parts: a central through shaft, to which the jaw is attached, and an annular piston sleeve. The housing is integrated into the main bucket shell, and the jaw is attached to the central shaft. The piston sleeve is sealed against the housing and shaft. As hydraulic pressure is applied, straight gears on the outside diameter of the piston sleeve and ring gear of the housing force the axial displacement of the piston — similar to the operation of a hydraulic cylinder. At the same time, the helical gearing on the shaft and piston inside diameter force the rotation of the shaft, opening the jaw. Applying pressure to the alternate port rotates the shaft in the opposite direction, closing the jaw. The shaft is supported by large, widely spaced integral composition bearings