ROBOT END EFFECTORS SCRIPT

Transcription

1 Slide 1 Slide 2 Slide 3 Slide 4 An end effector is the business end of a robot or where the work occurs. It is the device that is designed to allow the robot to interact with its environment. Similar in concept to human hands, end effectors allow a robot to grasp, move, tilt, lift, transport, and maneuver objects. It may hold a tool such a screwdriver or socket for tightening nuts or screws. It may be spot welding, arc welding, grinding a part, or spraying paint. The end effector equips the robot to perform specific tasks. End effectors may be designed to handle very small delicate parts or huge items that weigh thousands of pounds. There are an endless number of end effectors available for robots from a wide variety of manufacturers. When purchasing end effectors, they can be called Robotic accessories, Robotic peripherals, Robotic tools, and End of arm tooling (EOAT). Humanoids and service robots have advanced forms of end effectors which are designed to mimic the human hand. However, we will focus primarily on end effectors that are used with industrial robots. In this presentation you will learn: What end effectors are and how robots use them Types of mechanical finger grippers and how they simulate the human hand. The differences between collet grippers, magnetic grippers, vacuum grippers, and expandable grippers and how each is used. The degrees of freedom and dexterous workspace of a robot. The difference between revolute and prismatic joints used to attach grippers. Terms that are used to help describe how the robot performs motion. Examples of robot end effector tools used in industry. What robotic tool changers are and how they are used, and What robotic collision sensors are and how they are used. Throughout the presentation there is video of end effectors used in industry to illustrate many of these new concepts. Let s get started. Copyright 2010 Interactive Media Publishing page 1 of 8

2 Slide 5 Two broad classifications for end effectors are grippers and tools. Many robots are also equipped with tooling for automatic changeover. This allows the robot to select the type of tool or gripper required for a specific application and to change the end effectors for the task to be performed. Slide 6 Slide 7 Slide 8 For gripping, many designs take into account the gripping methods used by the human hand. However, most robotic grippers are a poor emulation. They re designed for dedicated purposes as opposed to having the broad general dexterity of the human hand. A huge variety of standard grippers are available from manufacturers. Grippers may also be customized to meet specific applications. The gripper shown here is a threefingered gripper. It is a Stäubli RX60 robot with a 7 DOF Schunk SDH gripper executing the grasp. Robot grippers are often selected by the amount of force that the gripper applies to a part. The style of the jaw that is used plays a major roll in determining the force required in a gripper application. Hard jaws provide precision but lack flexibility. Soft jaws offer compliance and allow for part variations, but may wear down sooner. Prehensility is the quality of an appendage or organ that has adapted for grasping or holding (like the tail of a monkey or the trunk of an elephant). The word is derived from the Latin term prehendere, meaning "to grasp." A gripper with good prehensility is well adapted for seizing or grasping - especially by wrapping around an object. Grippers may be classified and described by their prehensile abilities. In other words, the methods they use for grasping, the strength applied, and how well they grasp or hold particular types of objects. Here s a video of a type of robot arm whose design was based on the trunk of an elephant - called the Festo Bionic Handling Assistant. Its form lock gripper has great prehensility as demonstrated by grasping and moving an apple. Mechanical Finger Grippers are the most common type of gripper used to grasp objects. Mechanical finger grippers are parallel or angular closing with 2, 3, 4, or 5 fingers in either internal or external configurations. Fluid power or electricity may provide the force required for closing and opening the fingers. Copyright 2010 Interactive Media Publishing page 2 of 8

3 Slide 9 Slide 10 Slide 11 Slide 12 Two-finger grippers simulate the action of the human thumb and index finger. Three-finger grippers simulate the action of the human thumb, index finger and third finger. Four-finger grippers are like a pair of two finger grippers - with opposing fingers that close simultaneously. Five-finger grippers simulate the action of the human hand and can hold and grasp quite a variety of objects. Collet Grippers look similar to the end of a drill motor used to grasp drill bits. They are available in round, square, or hexagonal shapes and are used for gripping cylindrical parts that are uniform in size such as the shaft of a drill bit, screwdriver, or socket wrench. Collets are usually designed for gripping one specific diameter of parts(1, ½, etc.). They can also be used as a work holding device for sanding, deburring, grinding, or polishing operations. Magnetic grippers use an electric magnet which is turned on to pick up a part. The magnet is momentarily reversed to place or release the part. Magnetic grippers are used to pick up a large variety of metallic materials that contain iron such as hot iron parts, bottle caps, and mechanical parts (such as the parts of a vehicle). They may have additional tooling that orients a part to a certain direction as it is picked up and released. Here is an example of a magnetic gripper in action. Slide 13 Vacuum grippers use suction to pick up items such as fabric, sheets of plastic, sheets of wood or metal or glass, eggs, fragile parts, or irregularly shaped objects. It is usually lightweight and simple in construction and may have additional tooling that orients a part to a certain direction. Standard vacuum cups are available from various manufacturers in a variety of sizes. Slide 14 Watch this example of a vacuum gripper. Copyright 2010 Interactive Media Publishing page 3 of 8

4 Slide 15 Slide 16 Expandable grippers are used to pick up irregularly shaped objects and can be designed to grip from the inside or outside of the object. It consists of an expandable bladder which can be inserted into an object such as a cup, bottle, glass, plastic bottle or can. The bladder is inflated, the object can be moved, and the bladder is deflated to release the object. The joints in a robot provide movement and mobility and are a key component in the design of the robot because they enable it to perform a specific function. There are many different types of joints, and a wide variety of materials used to make these mechanical systems easy to operate, and to keep one part from rubbing against another. Joints provide the movement that distinguishes one robot from another. Slide 17 Robots are often defined by the types and number of joints they have, or the degrees of freedom (DOF). Each joint is often counted as one degree of freedom or DOF, so a 6 DOF robot will have 6 joints for movement. It is often the additional DOFs that are part of the gripper that allow a robot to perform specific tasks. These are usually not counted in the DOFs of a robot (because grippers are often purchased separately) but a gripper can have more DOFs than the robot itself. As you may recall, there are six terms used for degrees of freedom that define position and orientation of movement. The first three are x, y, and z. These define the position and location of an object left-right, up-down, and forward-reverse. The next three are for orientation and are called roll, pitch, and yaw. Yaw refers to the direction the object is facing and its orientation within the xy plane. Roll refers to whether the object is upright or upside down and its orientation within the yz plane. Pitch refers to whether the object is tilted to the left or right and its orientation within the xz plane. Workspace defines the areas or points that the robot can possibly reach within a defined space. The dexterous workspace is all of the possible points the robot can reach with an arbitrary orientation (x, y, or z). The dexterous workspace is usually a subspace, or only part of, the maximum reach space of the robot. Copyright 2010 Interactive Media Publishing page 4 of 8

5 Slide 18 Before we move on to other forms of grippers, let s take a look at how grippers are moved with manipulators (or actuators). A manipulator typically consists of two types of joints, connected by a link. Shown here are three different types of links. A link is simply a solid mechanical structure which connects two joints. The holes at the rounded ends of the link in these samples are where the joints are attached. The main purpose of a link is to maintain a fixed relationship between the joints at its ends (like a bone that connects the wrist to the elbow). At the end of the link closest to the base, a manipulator has a joint for movement. At the end furthest away from the base, instead of a joint, there is usually a place to attach a gripper (such as a tool plate). Slide 19 Slide 20 Most grippers are attached to a link of a wrist or arm with either a revolute or prismatic joint. A revolute (or rotary joint) rotates around an axis or center point. Most revolute or rotary joints cannot rotate through a full 360, but often are mechanically constrained to 180 or less. Rotary joints consist of a stationary part connected to the arm of the robot, allowing for electrical and pneumatic cables to stay in place, and a rotating part connected to the wrist and tool, allowing cables required for the tool to be free to rotate. A prismatic joint (or sliding or linear joint), moves in a straight line with the axis of the joint at the center line of the sliding link. Prismatic joints provide single-axis sliding function and are used in places such as hydraulic and pneumatic cylinders. Since any prismatic form can be used (such as rectangle, square, or round) it does not have a specific axis (like a rotary joint) but merely an axial direction. There are two basic configurations: the axis can be collinear (in a straight line with the fixed link), or it can be perpendicular (at a 90 angle to the fixed link). Here s an example of a revolute or rotary joint in action. Each of these cubes has a rotary joint in the section where there is a diagonal line going across the cube. This is a unique design for a robot arm where the cubes can be joined together for an endless variety of motion. An end effector can be attached to any side of the cube. Copyright 2010 Interactive Media Publishing page 5 of 8

6 Slide 21 Slide 22 Here s an example video from a manufacturer who produces both Prismatic or Linear Joints and revolute or rotary joints. The solar cell assembly operation at the end of this video demonstrates the two types of linear motion collinear and perpendicular. A robot is often trained to follow a particular route or trajectory to complete an assembly operation or as part of its usefulness in some type of service. There are some terms to know that are used to help describe how the robot performs. Self-motion is the robot's ability to move it's intermediate links while holding the placement of the end-effector constant. In other words, it moves the wrist, arm or shoulder, while keeping the end-effector in the same position. Dexterity is a term used to measure of the robot's skill of completing specific difficult paths. This is similar to how athletes are evaluated on their dexterity or ability to move such as a basketball center or guard. Slide 23 Slide 24 Kinematics is the study of motion. Inverse kinematics is a procedure which determines where the end-effector needs to be placed to reach a particular point in space. The procedures use mathematical algorithms along with sensors to determine the desired location of the point in space. Inverse Kinematics is often used during the design and programming of robots. It is something you will learn if you decide to go into robotic engineering. In many industrial applications, robot end effectors are tools designed to perform a specific task. In these cases, robots manipulate a tool and the tool is directly attached to the wrist. Once again, there are a large number of types and sizes of tools from a variety of manufacturers. Some industrial robotic tools include: Spot-welding tools Arc-welding torch Heating torches Rotating spindles for operations such as drilling, routing, wire brushing, grinding, and deburring Liquid cement applicators for assembly Copyright 2010 Interactive Media Publishing page 6 of 8

7 Water jet cutting tools Laser cutting tools Engraving tools Glue gun Nail gun Spray gun Screwdriver Drill gun, and Milling machine tools While robots may be designed for one specific task, more robots are being developed with the capability to exchange tools in a rapid manner. This flexibility has increased their usefulness. Slide 25 Here are some examples of End Effector Tools. Many more examples can be found by searching the Internet and viewing product descriptions from the manufacturers of end effectors. Slide 26 Here are additional samples of end effector tools. Slide 27 A Robotic Tool Changer is an end-effector with two mating parts - normally called a Master Side and Tool Side - that have been designed to lock or couple together automatically. Most use pneumatics (air force) to lock the Master and Tool sides together. The tool changer is also able to pass utilities such as electrical signals, pneumatic air, water, etc. to the tool. The robot tool changer provides flexibility for any automated process allowing the robot to change out tools for various applications. The Master Side of the tool changer mounts to a robot or other structure. The Tool Side of the tool changer mounts to tooling, such as grippers, welders, or deburring tools. A robotic tool changer is also known as an automatic tool changer (ATC), robot tool changer, robot coupler, and robotic connector. Copyright 2010 Interactive Media Publishing page 7 of 8

8 Slide 28 A Robotic Collision Sensor is an end effector or device that can detect a crash before or during a collision of the robot or its tools. It may be mounted between the joint and the end effector. It senses any object that comes within a predefined distance of the end effector. Collision sensors send a signal back to the robot controller before a collision, to have the robot avoid the collision or stop before or during a collision. They protect the robot from damage and also protect humans and the workspace. Robotic crash protection devices are sensors that detect the collision during the crash. A collision sensor is also know as a robot safety joint, robot overload protection device, crash protection device, quickstop, robot safety mount, robotic clutch, and robotic collision protector. Slide 29 In Summary, there is a wide variety of end effectors available for robots. We presented quite a few of the most common industrial grippers - collet grippers, magnetic grippers, vacuum grippers, and expandable grippers, among others. We reviewed the two most commonly used joints to attach an end effector revolute or rotary joints and prismatic or linear joints. We also saw a wide variety of tools available for robots, and two important accessories for end effectors - tool changers and collision sensors. Slide 30 Let s conclude this presentation by viewing a large complex robotic arm - the one used on the space shuttle Endeavour. The end effectors on this arm are customized for use in outer space. Then let s look at the R2 Robonaut that NASA is deploying to the space station. The articulated hands are quite advanced as this robot is designed to perform a variety of functions to assist astronauts. Copyright 2010 Interactive Media Publishing page 8 of 8