The terms "Gripper", "Adaptive Gripper", "Robotiq Gripper" , "S-Model", "3-Finger Gripper" and "Robotiq Adaptive Gripper" used in the following manual all refer to the Robotiq 3-Finger Adaptive Robot Gripper. The Robotiq 3-Finger Adaptive Robot Gripper is a robotic peripheral that is designed for industrial applications. Its design makes it a unique robotic end-of-arm tool to pick, place and handle a large range and volume of parts of varying sizes and shapes.
The Adaptive Gripper has three articulated fingers, i.e. finger A in front of finger B and finger C, that each have three joints (three phalanxes per finger), as shown in Figure 1.1. The Gripper can engage up to ten points of contact with objects (three on each of the phalanges plus the palm). The fingers are under-actuated, meaning they have fewer motors than the total number of joints. This configuration allows the fingers to automatically adapt to the shape of object they grip and it also simplifies the control of the Gripper.
Figure 1.1 : The Robotiq 3-Finger Adaptive Robot Gripper.
Two different types of movements can be performed with the Gripper. The first one simultaneously changes the orientation of fingers B and C as shown in Figure 1.2. That movement is referred to as changing Operation Modes. The Operation Mode is determined by the user prior to the grip in function of the size or the shape of the object and for the task that has to be done.
Figure 1.2 : First type of movement of the 3-Finger Adaptive Robot Gripper: changing the Operation Mode
- The basic mode is the most versatile Operation Mode. It is best suited for objects that have one dimension longer than the two others but can grip a large variety of objects.
- The wide mode is optimal for gripping round or large objects.
- The pinch mode is used for small objects that have to be picked precisely. This Operation Mode can only grip objects between the distal phalanxes of the fingers.
- The scissor mode is used primarily for tiny objects. This mode is less powerful the the three others, but is precise. In scissor mode, it is not possible to surround an object. Here, fingers B and C move laterally towards each other while finger A remains still.
The four pre-set Operation Modes can be chosen by the user (see Figure 1.3).
Figure 1.3 : The four Operation Modes of the 3-Finger Adaptive Robot Gripper.
The second movement of the Gripper is the closing and opening of the fingers as shown in Figure 1.4. This action is performed with a single input from a user. Each finger is not controlled independently; the Gripper itself closes each finger until it reaches a stable configuration, on an object or against the Gripper palm. Note that a user can specify the relative speed at which the fingers will close and the relative force that will be applied to an object.
Figure 1.4 : Second movement of the 3-Finger Adaptive Robot Gripper: closing and opening the fingers.
Two types of grips occur when closing the 3-Finger Adaptive Robot Gripper on an object: Fingertip Grip or Encompassing Grip.
- The Fingertip Grip is when an object is only held by the distal phalanxes. This type of grip is similar to what is done with conventional industrial parallel grippers. In this situation, the stability of the grip is mainly related to the friction between the fingers and the object.
- The Encompassing Grip is when the fingers surround an object. The object is encompassed within the fingers and the stability of the grip is no longer related to friction. We suggest using the Encompassing Grip whenever possible to increase grip stability.
Figure 1.5 shows the two types of grips.
Figure 1.5 : The Two Types of Grip, Encompassing and Fingertip Grips.
It is important to note that a Fingertip Grip can only be performed when the fingers touch the object with the distal phalanxes first. Inversely, for an Encompassing Grip, the fingers must touch the object with the proximal or medial phalanxes first. Also, to ensure stability, the object should be held against the Gripper palm before doing an Encompassing Grip.
Note that the Encompassing Grip cannot occur in all Operation Modes. Thereby, in Pinch and Scissor modes, it is only possible to do Fingertip Gripping. On the other side, the Fingertip Grip can occur in all four Operation Modes. Figure 1.6 summarizes the Types of Grip possible for each Operation Mode.
Operation Modes are inputs to the Gripper. Whether the fingers close to produce an Encompassing or Fingertip grip is decided at the Gripper level automatically. It will depend on:
In other words, picking the same part using the same Operation Mode could result in either an encompassing or fingertip grip based on a part's position and geometry.
Figure 1.6 : Operation Modes vs. Types of Grip.