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moldmakingtechnology.com 21 linear robots are supplied with 90-degree pneumatic rotation from vertical to horizontal, which is adequate in most pick- and-place applications. Yet, more often, additional degrees of freedom are required to conduct post-molding applications or to simply relieve the part from the mold. Many newer automa- tion applications have parts designed with detail that is not in the die draw, which requires the robot to "wiggle" the part off of the mold. This requires a servo wrist that essentially adds a two-axis articulated motion to the end of the vertical arm on a linear robot. The type of wrist paired with the robot can directly impact mold design. For example, it affects daylight, or mold-open distance, which is the amount of linear clamp stroke required to open the mold far enough for a robot to remove parts. A dual-opposing wrist design for insert molding can minimize the daylight opening by 25 percent, simplify programming and reduce mold-open time, all which improve cycle time. Considerations for wrist options include torque require- ments, wrist weight, weight of payload (parts and runners), and the extra daylight needed for wrist, payload and movement. In a nutshell, wrist choice is dictated mostly by application require- ments, but sometimes excessive torques or minimal daylight requirements can play a bigger role in this choice. These facts are often overlooked, resulting in premature failure of compo- nents or utter dysfunction of the automation. Press-mounted robots are becoming increasingly popular because they save foor space and their safe operation (guarding) makes them simple to implement. CONTRIBUTOR Rich Oles is owner of ROI Rich Oles Industries LLC. He has 30 years of experience working directly with injection molders and moldmakers in a variety of industries around the world. Jason Holbrook, a sales manager for Krauss Maffei, has a 20-year history in plastics machine technologies and automation, along with a diverse injection molding experience in several key end markets, including automotive, appliance, packaging, medical and consumer products. LEARN MORE Robotics Options and Requirements Visit short.moldmakingtechnology.com/ p2probots for more on the information presented here. Tolerances in automation cell design are another consider- ation. A robot has a given operational positioning tolerance. However, this typically cannot be relied upon for position accuracy in the cell, because the entire cell's stack-up of toler- ances are often far beyond the controlled allowances of the final part print. Also, keep in mind that the robot is sitting on a moving machine. Thus, for a tight toleranced automation cell, it is better to eliminate the robot from the stack-up of tol- erances by considering the robot as only a carrier of the EOAT in which the EOAT, mold and automation fixtures are operat- ing parts of an isolated system. To ensure tighter tolerances, locating pins are often used to ensure proper datum location among the three pieces of that three-part isolated system. Vibration is often the leading challenge to position tolerance. Consider that a robot mounted to a machine platen has a mov- ing piece of machinery under it, so it's no surprise that hold- ing a position tolerance is difficult. Forces of an operational molding machine travel in a sine curve. When that sine curve terminates at the EOAT, it becomes high-frequency vibration. Reason: the sine curve movement of the molding machine transfers through masses of metal, and more mass allows low frequency, while less mass promotes high frequency. As that sine curve of vibration moves from fixed platen to robot riser to traversing beam to kick stroke to vertical arm and then to the EOAT, the mass is reduced exponentially, and this exces- sively increases vibration. The solution is to ground the vibra- tion by adding a support leg with enough mass in proportion to the robot. This provides a path for transfer of those forces to a vibration-isolation pad to the floor. The bigger the leg, the more the mass, the easier it travels and the less vibration. These basic robot considerations will help the molding team provide a complete and consistent molding process. FOR MORE INFORMATION: Rich Oles / ROI Rich Oles Industries LLC 616-610-7050 / richoles@gmail.com / Skype: richard.oles Jason Holbrook / Sales Manager / Krauss Maffei Corp. 859-653-4309 / jason.holbrook@kraussmaffei.com VIDEO: A/C Servo Combination Wrist in Motion short.moldmakingtechnology.com/acwrist