When moving products or packages in an industrial setting, properly matching a robot’s end-of-arm tooling to the materials being moved improves application effectiveness. That may seem like common sense, but hoisting or stacking different materials requires careful consideration of many essential variables to avoid accidents, injuries and downtime.
Primary considerations include:
• Work piece shape
• Work piece material/structure
One of the most common end-of-arm tooling options is the gripper. What is a gripper? Simply stated, a gripper is an interface between a robot or machine and the physical world. A gripper acts on the work piece (product or package), allowing the robot to hold and manipulate it as it performs a series of tasks.
It would require an in-house expert to review every option, setting and scenario of your operations, and how those elements can dictate your choice, but this baseline can give you the tools you need to begin evaluating your pick-and-place needs.
Now, let’s discuss whether mechanical grippers or vacuum grippers are best suited to solve your pick-and-place packaging challenges.
Mechanical grippers use two or more “fingers,” also known as jaws, that close and grip the product or package. They are a cost-effective and reliable option for many standard pick-and-place packaging applications.
A mechanical gripper can maintain a firm hold on products or packages during high-speed movements and their powerful jaws can lift and hold heavy items, but are in danger of crushing delicate items without proper calibration. They can pick and place pieces with varying thickness without changing the gripper, but oddly shaped items may present a challenge to static jaw shapes and angles.
Mechanical grippers must operate in the same environment as the work piece, creating potential failure modes, and need enough room for the jaws to actuate. Additional space is necessary to allow it to grip a work piece from multiple sides.
Mechanical grippers are driven by any of three power sources:
• Pneumatic—Because most plants employ compressed air, pneumatic mechanical grippers are the most common and provide easy implementation, but do not always provide precise control.
• Electric—Electrically driven mechanical grippers provide precise control, but are more expensive and must be contained within a larger package, resulting in challenges to the program or operation.
• Hydraulic—Hydraulicgrippers provide high forces and are capable of lifting larger loads, but they are costly to purchase and maintain, and have the potential for fluid leaks.
Mechanical grippers are also available in four different styles:
1. Two-finger (jaw) angular—Easy to apply, capable of picking different sized parts with the same jaw, and moderately priced; require more space than vacuum grippers.
2. Two-finger (jaw) parallel—Versatile, able to pick the outside or inside of a part, suitable for smaller spaces and flexible enough to pick different sized parts with the same jaw; more expensive and may crush softer or more fragile products/packages.
3. Three finger (jaw) parallel—Helpful when proper positioning is required to move the item; requires the product/package to be properly oriented and positioned for secure grip, and can potentially crush delicate work pieces.
4. Two-finger (jaw) locking—Jaws lock when closed and hold parts firm even if power is lost; higher price point and requires more space than vacuum grippers.
Unlike mechanical grippers, which use jaws to grasp and move items, vacuum grippers use soft foam rubber, plastic plenums or vacuum cups to pick up materials without damaging them. They are ideal for applications with extreme weights (very heavy or very light) or delicate work piece materials, where mechanical grip strength is too low to pick pieces or too high and causes damage.
Vacuum grippers are more versatile than their mechanical counterparts. They can adapt to smaller or larger items by adding additional cups or adjusting flow. Mechanical grippers can sometimes cause damage to the items they pick, but vacuum grippers can pick parts that are delicate or thin without causing damage. Vacuum grippers only need access to one side of a item, allowing them to pick products/packages more easily; on the downside, this sacrifices flexibility that could cause the item to drop. Additionally, small dense parts may not offer enough surface area for a vacuum gripper to pick the part.
Vacuum grippers can also be configured specifically for different environments. Vacuum cups are made from a variety of materials that can be compliant with the Food and Drug Administration (FDA) or meet other regulatory requirements. The vacuum pump can be installed away from the pick point to protect it from environmental hazards.
Vacuum grippers rely on either electricity or compressed air for power. Electric vacuum grippers do not require cumbersome or awkward hoses to operate. The downside of this is low flow, which may make the gripper too weak to pick up some items.Compressed air vacuum grippers, on the other hand, can operate with high vacuum levels, enabling them to pick up heavy products/packages and provide greater flow for picking up parts that are porous.
Vacuum grippers have other variables that need to be considered when making a selection. Some grippers rely strictly on vacuum cups or foam pads to operate. Vacuum cups are easy to service and are highly precise in their operations, making it possible to choose ideal pick points on the work piece to prevent damage. They also come in a variety of shapes, sizes and materials that can be suited for most applications.
Vacuum grippers may also be found with foam pads. These can conform to the shape of the product/package and allow picking a variety of items with a single tool. However, they are not as capable of precise placement when compared to suction cups.
Other less common vacuum gripper options include:
• Soft grippers, which use vacuum to actuate silicone fingers to conform to the product/package, making a gentle and flexible picking solution.
• Magnetic grippers, which employ large magnets to pick up strong materials. An actuator pulls the magnet away from the work piece, thus releasing that part.
• Bladder grippers, whichfeature a rubber bladder inflated inside a work piece to pick the part. Deflating the bladder releases the item.
It can be difficult to determine exactly what components are right for your packaging applications. But, using these guidelines, you should be on the right track to building your perfect pick-and-place device.
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