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Design News, May 2013

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Fluid Power/Motion Control Most manufacturers of gripping devices offer their products in both Next, a decision must be made to deterparallel and angular jaw models. This mine how many jaws will be required. choice is typically made based upon the Will the solution require two jaws, geometry of the part and the number three jaws, or more? The vast number of of parts that will applications can be be gripped. While accomplished with a two-jaw gripper, THE DESIGNER MUST angular jaw travel grippers tend to be which can be easily CONSIDER ONE OF the least costly, they tooled to accommodate square, rectanTHE MAJOR CRITERIA also tend to be the least versatile when gular, round, or even FOR SELECTING AND tooling is applied. If irregularly shaped components. A three- SIZING AN AUTOMA- the device will always the jaw gripper can be TION GRIPPER, THAT be grippingsamesame part at the positooled to grip round or irregularly shaped BEING THE PAYLOAD. tion, and the size of that part doesn't vary parts, but is not well by any great degree, suited for square or then properly designed tooling on an anrectangular parts. Very rarely is there a gular jaw motion gripper can be the best need for more than three jaws. choice. If the size of parts can vary or if A big consideration is cost and availability of devices offering more than two the requirement is to be able to accommodate more than one part on demand, jaws. Along with the number of jaws, then perhaps a better choice would be the designer will then decide whether a parallel jaw motion device. Many the application needs an external or designers believe that a parallel jaw internal gripping motion. Due to piston motion is the only safe way to interface rods attaching to mechanical linkages with round parts, but a properly tooled or cam configurations, many pneumatic angular motion can be just as effective. grippers will have higher grip forces in When deciding on angular or parallel one direction than the other. Or they jaw motion, it is also important to determay include a specific option designatmine part encapsulaing higher grip force tion and total jaw in one direction travel. These two asversus the other. pects are very closely ANGULAR VS. related during sizing PARALLEL and selection. EnThe next considcapsulation refers to eration is usually whether the gripped jaw motion. The part will be mechandifference between ically interlocked the two motions by the gripper jaw is the way the jaws tooling or a simple travel with respect to surface-to-surface each other and the friction grip between way their gripping the jaw tooling face faces relate to the and the user's part. parts being gripped. Grippers: Pneumatic grippers are avail- When sizing a gripable in many sizes and are offered in Angular grippers per, required safety both parallel and angular jaw models. have jaws that pivot factors usually take from the body of the gripper and travel encapsulation into account. Generally, a through an arc until the tooling encoun- higher safety factor should be used when ters the part. Parallel grippers have jaws relying strictly on a frictional grip. Also, usually at right angles to the body of the a coefficient of friction between the jaw gripper, and travel through a common tooling and the part being gripped is parallel plane until the tooling meets the required to calculate the resulting fricpart. tional grip force. trusted TECHNOLOGY advanced PERFORMANCE For the highest torque-to-size ratio, choose a tooth clutch or brake. SEPAC has the experience to capture this advantage and help you spec our designs seamlessly into your products and equipment. Call us today. www.sepac.com 800.331.3207 magenta cyan yellow black F8 F L U I D P O WE R / MO T IO N CO NT R O L / A S UP P LE ME NT TO DE S IGN NE WS SOURCE: PHD JAW CONSIDERATIONS

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