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Choosing Robot Grippers

Learn about the different types of robot grippers—pneumatic, electric, vacuum, soft adaptive, and magnetic—and how to select them based on capabilities and robot/automation supplier relationships.

   

Read the full transcript below 


David Greenfield: Welcome to the Automation World Gets Your Questions Answered podcast, where we connect with industry experts to get the answers you need about industrial automation technologies. And you can find even more answers by subscribing to automation world at Subscribe AutomationWorld.com

I'm David Greenfield, Director of Content for Automation World. And the question we'll be answering in this episode is how to choose robot grippers.

Now joining me to answer this question is Michael Guelker with Festo, a supplier of industrial automation technologies ranging from electric pneumatic and servo, pneumatic actuators and robot grippers to servo motors and drive sensors and controllers. So thanks for joining me today, Michael. 

Michael Guelker: And thanks for having me, David. 

David Greenfield: So before we get into the specifics about different gripper types, let's first talk about how to approach robot gripper selection based on the application. So can you explain how engineers or operators, you know should first look at what the gripper will be used for to help narrow down their gripper options?

Michael Guelker: Yeah, so you know, gripping always begins with the workpiece. So what do you need to pick up? You know, so what's the size, the mass and material? And then there's different design constraints as well. So you know, what kind of max speed and acceleration is it going to be exposed to the cycle rate, how many cycles per minute, the precision that's needed? You know, what about drop protection, if you lose power, things like that, then there's also environmental factors. So once the temperature that it's going to operate in will be exposed to contamination, you know, dirt, dust, oil or moisture, will be exposed to cleaning processes or chemicals? Does the application require antistatic materials like handling electronics, things like this? And then there's other factors to consider as well, our cost, of course, you know, what's the upfront cost, the operating and maintenance costs as well as energy consumption?

You know, so all of these factors will lead you to the best type of gripper for the application. Whether it's a mechanical gripper, vacuum, magnetic or soft and adaptive type of gripper. Then you can get into the specifics to select a particular gripper product or solution to meet your needs there. So oftentimes, the gripper manufacturer will offer software sizing tools to help you select the best gripper based on the application parameters. 

David Greenfield: And, you know, before we get into the, the gripper types, you know, let's look at just the robot types. And, and by that, I mean, you know, industrial robots are collaborative robots. Does the type of robot technology you use, you know, have an impact on what your gripper options are? Or is it more about the ease of gripper integration onto the robot based on technology partnerships between the gripper and robot suppliers?

Michael Guelker: With collaborative robots, you know, since these are often used in close collaboration with people safety as a major consideration, this means that the gripper or the end effector doesn't have any sharp edges or pinch points. And then the other safety aspect is the potential loss of power shouldn't result in a dangerous failure, where the object is dropped unexpectedly. In addition to the safety aspect, collaborative robots, they're often used by companies and people without extensive robot or automation experience. So the grippers must be simple to integrate and commission. As you mentioned, some robot manufacturers have partnership programs within the various tooling manufacturers, providing direct mechanical interface of the gripper to the robot as well as a software plugin which enables simple plug and work commissioning. With industrial robots. They have similar ISO standard mechanical interfaces as Cobots. So the integration is similar, but without the software plug in. So that needs to be developed by the integrator. Another factor is that industrial robots can typically move much faster than Cobots. So the speeds and accelerations need to be considered when selecting and sizing the gripper. 

David Greenfield: So with those questions addressed, you know, let's now you know get into the different gripper types and the kinds of applications they're best suited for, and let's start with the pneumatic and electric mechanical grippers, which tend to be the kind of grippers that you know most readily come to mind when you think of a robot gripper. So how do these types of grippers work and what kinds of applications are they typically best suited for? 

Michael Guelker: As for how they work—Mechanical grippers that convert a linear or rotary motion to the gripper Jaws via some type of mechanical linkage, or maybe a wedge cam mechanism, or a rack and pinion. And the driving force can be pneumatic with a piston or it can be electric via motor and a gear. With a pneumatic grippers, they're actually the most common they make up around 85% of the market, they tend to be more lightweight and cost effective than their electric counterparts. They also feature higher grip forces can handle faster cycle rates that are more suitable for the harsh environments.

Electric grippers on the other hand, they can offer greater precision, as well as motion control capabilities such as speed force and position control. They do tend to be a little bit heavier due to the presence of a motor and other internal components which also increases their upfront costs. So grip force to weight ratio is best with pneumatic grippers. And eliminating the weight of the end of arm tooling is always a big priority as this impacts the size of the robot and other components, as well as the max potential speeds and acceleration lighter is always better.

You know whether it's electric or pneumatic mechanical grippers typically utilize lightweight gripper fingers made of aluminum or maybe a 3d printed polymer. The fingers are often designed according to the shape of the object to be handled. So mechanical grippers are typically best suited for applications where the same or a similar object is being handled.

Mechanical grippers generally offer a higher precision compared to other gripping methods like vacuum and magnetic.

David Greenfield: So it sounds like you were describing those the difference between electric and pneumatic type grippers that a lot of the performance characteristics are much like the difference between any type of electric or pneumatic actuator whether it's a gripper or not, is that accurate assumption or is there a difference when it comes to grippers? 

Michael Guelker: Yeah, no you're right on there. Yeah, the difference is very similar. You know pneumatics provides high power density, so high force and a small package. The electric gives you more flexibility to control things controlling force and speed and, and things like this. 

David Greenfield: Okay, thanks for explaining that. So now let's look at the vacuum grippers you know, which are typically seen being used to gently pick up you know, softer objects. How do these grippers work and when should they be considered the gripper of choice for an application. 

Michael Guelker: Vacuum grippers Use Suction cups or pads with vacuum generators or pumps. The vacuum pressure is generated with positive pressure that runs through a venturi nozzle, or it can be generated with an electric pump.

Vacuum grippers may be as simple as a single suction cup, multiple suction cups or large modular matrix of cups. The vacuum pads are typically larger and rectangular in shape. For applications like palletizing, where you're handling one or more boxes. When it comes to the suction cups. You know, it's important to consider the nature of your workpiece as well as the environment when you select the material. Buna rubber suction cups for example, they're ideal for oily or a plain type of workpiece, where silicone is suitable for food, as well as hot or cold objects. And there is of course, an assortment of other materials available for different circumstances. The cup shape is also an important factor, especially when it comes to gripping objects that are maybe flat versus round or, you know slim versus large, something that's very sturdy versus a delicate object that can also impact the cup selection. The vacuum grippers are inexpensive, compact and flexible. So they're ideal for limited workspaces, and they can handle a variety of objects at high speeds. At the same time, however, vacuum grippers can run up your maintenance and operating costs. You know the suction cups that are susceptible to quick wear and they need to be replaced. While the generators they can consume high rates of compressed air and they can also clog up if there's a dust or other contaminants in the air. So the vacuum grippers are really well suited for basic handling applications. Or if the like high precision is required. Then you may be looking at a mechanical gripper much like you know vacuum grippers are used to pick softer, more easily damaged objects.

David Greenfield: Soft adaptive grippers seem to offer a blend of mechanical gripper technology with the ability to gently handle items like a vacuum gripper does, you know what can you tell us about the soft adaptive grippers and for what types of handling applications are they best suited? 

Michael Guelker: Yeah, so soft and adaptive grippers. It's a really hot topic nowadays. You know, there's a really a great deal of innovation in this area right now. There's a lot of demand automate handling and picking applications, especially with labor shortages and increasing costs there. You know, the food and E commerce segments are really driving a lot of that demand right now.

Soft grippers like you mentioned, it's really a type of mechanical gripper. But they have soft, flexible, typically polymer fingers. So they can handle delicate objects without damaging them.

You know, they're very common and food applications might be picking strawberries, or mushrooms or packing apples, things like this, were adaptive grippers they have the ability to handle a variety of different products. So this is really ideal for E commerce, you might be, you know, there could be various different products that have to be picked and placed into a box. And so the adaptive is kind of like a universal gripper, it can pick up all different types of products.

So the soft and adaptive grippers, they can handle workpieces of various shapes, sizes and orientations. So it enables automation on areas where it previously didn't exist.

You know, because they don't have any hard surfaces or sharp edges that are really well suited for handling food, glass and other delicate objects without causing any kind of damage or marking the surface. Compared to mechanical variants. However, the soft grippers are less precise and typically operate at a little bit slower speed.

David Greenfield: So finally, let's look at magnetic grippers. You know, this is a type of gripper I haven't seen as often as the other types we've been discussing here today. How do these magnetic grippers work? And you know, what are they typically used for? 

Michael Guelker: So magnetic grippers, they're used for handling or holding ferrous metal objects, so such as steel or cast or wrought iron. Some common items include sheet metal, in large or odd shaped metal parts. You know, one of the advantages of using magnets is one sided gripping or clamping, compared to mechanical grippers or clamps where you need to be in contact with two or more sides of the object.

Regarding how they work, there's two primary designs. There's a permanent magnet design that contains a magnet that's always on. And the magnet and the gripper is simply moved away from the object using a pneumatic or an electric actuator. So it's essentially removing the magnetic field just by moving it.

These are simple and inexpensive, but the magnets never off just away from the part. So they can, you know, collect metallic dust or chips. And that can cause early failure, or maybe scratch the parts as well.

There's the other popular design is from mag switch, and it uses two round magnet pucks just envision like hockey puck shape.

It functions by aligning or misaligning, the North and South Poles have the two magnets. So when you when you align the north and south poles, then it's magnetized and it's on. And when you misaligned them, then the residual magnetism is gone. So there is no magnet there.

Typically, a pneumatic swivel drive is used to rotate one of the magnets. And this design is really is nice because it provides a true on off capability. So you don't have that contamination concern. And it also offers higher forces since you have the two magnets there. 

David Greenfield: And I would imagine too, with magnetic grippers that it's it's they're energized when they're actually picking up objects and the de energize to release them is that the way they work to pick an object, hold it and then release it. 

Michael Guelker: Yeah, that's right. So the difference is with a permanent magnet, the magnets always on and the magnet gripper is simply moving the magnet farther away from the object to quote, turn it off, but it's actually always on. Whereas with the mag switch, you are rotating one of the magnets, and that's basically turning the magnetism on or off. So you do have a true off that way.

And the nice thing with the mag switch is, you know, it's pneumatically controlled, so it's not consuming energy while it's either energized or de energized. So you can turn the magnet on, and then it's on forever and you don't have to have compressed air or anything to it. So you have that security that if you lose power, you know, the magnets still energized with that design. 

David Greenfield: So, Michael, one last question, you know, early in our discussion we talked about supplier relationships between gripper suppliers and robot suppliers, you know, since they often tend to be separate companies. So should end users look for a universal type grippers that can be used with most robot types, or does it make sense to focus on gripper technologies from companies that have technology partnerships with the robot suppliers? 

Michael Guelker: Yeah, so just to clarify, you know, the term robot supplier is typically referring to articulating robots, you know, with Rotary joints or axes, you know, the most common type being a six axis robot from suppliers like FANUC, KUKA, Yaskawa, ABB, UR and others. You know, other types of robots are also commonly used with grippers such as Cartesian robots. These have linear axes like X, Y and Z, and the gripper attaches to one of these axes, most commonly the vertical Z axis.

With the with the Cartesian robots, the gripper integration is unique to each component and gripper combination. And using the linear axis and the gripper from the same manufacturer can simplify the integration, standard adapter plates might be offered.

But getting back to the articulating robots, these typically use an ISO international mounting interface for the end of arm tooling like grippers, you know, so mechanically, the interface is essentially a universal mount for robots from different manufacturers. The benefit of the technology partnership programs with the robot suppliers is that a software plugin is included, which makes the software integration and commissioning simple. So for the simplest integration, it's definitely best to select grippers or the end of arm tooling from these technology partners.

Even if an off the shelf solution won't meet your application needs, those technology partners will be best suited to like modify a design or develop a unique solution, since they already have the software plugin expertise to support you. These technology partnership programs, they've been very successful in my view, I expect to see these adopted by more if not all the manufacturers, as well as more end of arm tooling suppliers to join the programs and expand their offerings. 

David Greenfield: Well, thanks for clarifying that, Michael and thanks for to for bringing up the mention of Cartesian robots. You know, so much, focus in the robotics industry is on the articulated robots, Delta robots, and SCARA robots that sometimes it's almost easy to overlook the Cartesian robots which are really you know, workhorses in the robotic side of industry. They're used for so many different you know, assembly applications and others in a variety of industry.

So thank you again for joining me for the podcast, Michael, and thanks, of course, to all of our listeners, and please keep watching this space for more installments of Automation World Gets Your Questions Answered. And remember that you can find us online at AutomationWorld.com. And subscribe to our print magazine at SubscribeAW.com to stay on top of the latest industrial automation technology insights, trends, and news.

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