What is a gripper?
In the simplest terms, grippers are devices that enable robots to pick up and hold objects. When combined with a collaborative robot (or 'cobot') arm, grippers enable manufacturers to automate key processes, such as inspection, assembly, pick & place and machine tending.
It's useful to think of grippers as similar to the human hand; they are positioned at the end of the arm and allow you to combine the strength of an arm with the dexterity of a hand. This combination opens up a huge range of possibilities for material handling with cobots, from stacking large boxes to handling tiny, delicate electronic components.
There are many different types of grippers available to use with UR cobots. Some grippers' designs are just like human hands, complete with five fingers, but this isn't always the case. There are grippers with two and three fingers, grippers shaped like claws, mechanical gripper types, grippers with large suction cups and even grippers that look like air-filled bags. With so many to choose from, it can be difficult to know which robot gripper types are best suited to which applications.
In this article, we will look at the most popular grippers in manufacturing. We'll also summarize some of the options manufacturers have when selecting a gripper and we'll explore some of the pros and cons of different robot gripper types for different applications.
TYPES OF GRIPPERS
Choosing a gripper for your cobot can seem like a daunting task, especially with so many different types of grippers in robotics and so much overlapping terminology.
However, for general purposes, grippers can be divided into 5 main types, with each type being distinguished by the methods used to power and/or control the gripper itself.
Vacuum grippers use the difference between atmospheric pressure and a vacuum to lift, hold and move objects. Typically, the vacuum (or 'vacuum flow') is generated by a miniature electromechanical pump or a compressed air-driven pump. The vacuum flow must be uninterrupted to ensure that your cobot can safely hold on to the object it has picked up.
Compressed air-type grippers produce between four and ten times more power than their electromechanical counterparts, which makes them a good fit for lifting heavy weights. However, electromechanical-driven vacuum grippers shine in applications requiring a high degree of mobility.
You will find vacuum grippers being used to automate a wide range of tasks, but one of the most popular applications for this type of gripper is packaging and palletizing.
For example, Norwegian meat producer Nortura deployed a UR10 cobot fitted with a vacuum gripper to optimize its palletizing operations.
Using a UR10e fitted with a vacuum gripper for packing, DCL Logistics achieved a 500 percent efficiency increase, a 50 percent labor savings, three months ROI, and 100 percent order accuracy.
Advantages of vacuum grippers include the ability to handle many different types of items (even when those items are imperfectly positioned) and a lower price compared to other types of grippers. Disadvantages include added electricity costs to power compressed air or vacuum pumps and sensitivity to dusty conditions.
A pneumatic gripper uses compressed air and pistons to operate its 'jaws' (also known as 'fingers'). Most commonly found in 2-finger and 3-finger configurations, pneumatic grippers are versatile tools that can be used in a wide range of applications.
For example, Toolcraft Inc, a small machine shop based in Washington, USA, chose the PHD PneuConnect pneumatic gripper to automate a tricky, three-operation machine tending task inside a CNC machine. Combined with a UR5e cobot (which provides repeatability down to 30 microns), the system was able to place parts in the CNC and when the CNC machine had finished its work, dip the finished part into a rinsing solution and pass it through an air jet before finally placing the washed and dried part on a rack for shipping.
Pros of pneumatic grippers include low cost, large grip force range, ability to operate in tight spaces and fast response times. However, pneumatic grippers are best suited to handling single part types, so they might not be a great fit if your facility produces a lot of low volume/high mix items. This gripper type also provides limited force and position control and requires compressed air to function.
Powered by hydraulic fluids, hydraulic grippers provide more gripping power than their pneumatic counterparts, making them ideal for heavy duty applications.
The main advantage of hydraulic grippers is their excellent gripping power, but with that power comes some disadvantages, including the added complexity of handling oil, a pump, and a reservoir. Consequently, hydraulic grippers tend to be higher maintenance than other gripper types.
Electric grippers are a popular choice for many cobot applications including machine tending and pick & place. While they don't offer the same level of gripping power as hydraulic grippers, they are suitable for applications that require high speed and light/moderate gripping force. Electric grippers usually come in two-jaw and three-jaw configurations, with 3 jaw grippers often being chosen when round/cylindrical objects need to be handled.
For example, STAMIT, a machine tooling company based in the Czech Republic, used a 2-finger electric gripper from Robotiq and a UR10 cobot to take care of CNC machine tending tasks in its high mix production environment (4,000 differently tooled objects and 12 million parts total, each year).
Robotiq's 2F-85 electric gripper enabled STAMIT to improve productivity, reduce downtime and free its workers to concentrate on more interesting tasks.
The defining feature of electric grippers for manufacturing automation is control. Most electric grippers come with microprocessors that enable you to vary gripping force and speed. The addition of a force sensor enables electric grippers to easily handle different part types. On the other hand, while electric grippers are getting more powerful every year, in general they tend to provide less gripping force than pneumatic grippers and they also tend to be more expensive.
A note on gripper terminology
We've separated the gripper types above based on the methods used to power the gripper, but there are other ways to distinguish gripper types, such as by form, which results in terms like 'parallel gripper', 'soft gripper' and 'angular gripper.' You may also have encountered terms like 'adaptive gripper', 'mechanical gripper' and 'claw.' Don't worry about this extra terminology for now; it will be covered in the sections where we dive into more detail on different gripper types.
HOW TO CHOOSE THE RIGHT ROBOTIC GRIPPER?
There are several factors to keep in mind when choosing a gripper, but the most important is to be led by the specific application you have in mind. Universal Robots makes this easy for you through the UR+ ecosystem, which provides a wide range of grippers specifically designed to handle the most common manufacturing tasks. Nevertheless, there are still some important questions to ask when selecting a gripper for your cobot:
- Will the gripper be handling a single item or a mix?
- What types of items –foodstuffs, electrical components, for example-- will be handled?
- What shape are the items that you need the gripper to handle? (Flat, curved, irregular)
- Do you need data feedback from the gripper itself?
- What payload will the gripper need?
- Will the gripper need to operate in tight spaces?
TYPES OF END EFFECTORS
The term 'end effector' or 'End-of-arm Tooling' (EOAT) is used to describe any device attached to the end of a robot arm. Grippers are one type of end effector, but there are many others. For example, a smart camera attached to the end of a robot arm could be used to help with inspection tasks. Or a welding tool end effector could be attached to a cobot and used to safely automate welding tasks.
The Olympus UR Welding System ships with a welding end effector that's perfect for many simple welding applications.
Other end-effectors are used for dispensing. The AIM FD400, for example, is designed to provide accurate delivery of medium viscosity fluids (such as grease and silicone) within a production setup.
The FD400 doesn't use compressed air, which reduces variance caused by air pressure and enables extremely accurate dispensing control.