Rotary actuator kicks the bucket into high gear

May 11, 2006
Buckets with cylinderactuated moving jaws have been used on front-end wheeled loaders and backhoes for many years.

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.

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:

  • It generates tremendous output torque from a very compact configuration while producing consistent torque through the jaw's entire arc of movement — there is no variation in clamping force as the jaw moves.
  • There are no external moving parts (cylinder rods, hinge pins, or bushings) exposed to debris and damage.
  • There are no crossbars inside the bucket shell or on the movable jaw to obstruct loadingor discharge of materials.
  • All gear teeth remain engaged at all times to equally distribute loads, for resilience to shock loading.
  • Equal force is applied to both sides of the jaw, preventing damage when irregularly shaped objects are clamped.
  • Holding force is almost four times the clamping force; it requires approximately four times the force to backdrive the actuator as is required to drive it forward.
  • With the internal gears constantly bathed in hydraulic oil, the operating mechanism is virtually maintenance-free; grease ports at each end of the shaft permit contaminants to be flushed from the bearings.
  • Hydraulic protection is provided by the integral load holding and pressure control valves. 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.

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