Module 1RDSP.pdf

Robotic Drive System and Programming [ Professional Core ]  Module : 1 Introduction Robot Drive Systems  Course Contents Introduction to drive system Introduction of drive system, structure of drive system, necessity of drive system, dif...

Robotic Drive System and Programming [ Professional Core ]  Module : 1 Introduction Robot Drive Systems  Course Contents Introduction to drive system Introduction of drive system, structure of drive system, necessity of drive system, different types of drive system, design and consideration of drive system, advantages and limitations of drive system. Robot Actuators: Types of actuators, actuators quality, characteristics of actuating systems. INTRODUCTION ROBOT DRIVE SYSTEMS The actions of the individual joints must be controlled in order for the manipulator to perform a desired move its body, arm, motion and wrist. This provided by the drive system used to power the robot. Common drive systems used in robotics are electric drive, hydraulic drive, and pneumatic drive. The joints are moved by actuators powered by a particular form of drive system. Types of Actuators *Electric Motors, like: Servomotors, Stepper motors or Direct-drive electric motors *Hydraulic actuators *Pneumatic actuators  MECHANICAL DRIVE SYSTEMS The drive system determines the speed of the arm movement, the strength of the robot, dynamic performance, and, to some extent, the kinds of application. A robot will require a drive system for moving their arm, wrist, and body. A drive system is usually used to determine the capacity of a robot. For actuating the robot joints, there are three different types of drive systems available such as: (i) Electric drive system, (ii) Hydraulic drive system, and (iii) Pneumatic drive system. The most importantly used two types of drive systems are electric and hydraulic.  ELECTRIC DRIVE SYSTEM The electric drive systems are capable of moving robots with high power or speed. The actuation of this type of robot can be done by either DC servo motors or DC stepping motors. It can be well –suited for rotational joints and as well as linear joints. The electric drive system will be perfect for small robots and precise applications. Most importantly, it has got greater accuracy and repeatability. The one disadvantage of this system is that it is slightly costlier. An example for this type of drive system is Maker 110 robot.  HYDRAULIC DRIVE SYSTEM The hydraulic drive systems are completely meant for the large – sized robots. It can deliver high power or speed than the electric drive systems. This drive system can be used for both linear and rotational joints. The rotary motions are provided by the rotary vane actuators, while the linear motions are produced by hydraulic pistons. The leakage of hydraulic oils is considered as the major disadvantage of this drive. An example for the hydraulic drive system is Unimate 2000 series robot.  PNEUMATIC DRIVE SYSTEM The pneumatic drive systems are especially used for the small type robots, which have less than five degrees of freedom. It has the ability to offer fine accuracy and speed. This drive system can produce rotary movements by actuating the rotary actuators. The translational movements of sliding joints can also be provided by operating the piston. The price of this system is less when compared to the hydraulic drive. The drawback of this system is that it will not be a perfect selection for the faster operations.  NECESSITY OF DRIVE SYSTEM Electric drives have many excellent properties that make them a preferred choice. However, there are other types of drives based on other physical principles that also have their own strengths. Note that the benefits and downsides are always somewhat relative. What is a major advantage in one application can be totally irrelevant in another application and vice versa. The evaluation also strongly depends on the power/torque/force range that we are looking into. In fact, an actuator is a device converting certain form of power into motion. Therefore, an actuator is a fundamental part of a drive (system).  HYDRAULIC DRIVES In hydraulic systems the power is transmitted through the hydraulic fluid. Hydraulic system as an actuator is a preferred choice in heavy duty applications with extreme forces or pressures. We can find them in construction machinery, mining equipment (e.g. excavators), forge presses, marine propulsion, special manufacturing equipment or transport. They drives are simply used when a brute force is required. Hydraulic drive transformers pressure into motion by using a pressurized fluid. The fluid has negligible compression. Most common fluid is a hydraulic oil. Basic components of a hydraulic drive are: cylinders with pistons, gear and vane. Hydraulic actuators achieve the highest force and power density (horsepower-to-weight ratio).  HYDRAULIC DRIVES High power density / best power/weight ratio Very high forces can be transmitted Linear movement without the need of additional transmission elements Portable (mobile) systems - e.g. truck mounted Immune against harsh conditions Starting under heavy load possible Drive can hold the load Contamination of oil as working medium / Use of oil filters required Environmental concerns in case of oil leakage Higher maintenance effort and cost Expensive control systems required to achieve accuracy Slow operation  PNEUMATIC DRIVES Pneumatic systems use compressed gas, usually air, as working medium. The inlet air is of normal atmospheric and is compressed to a much higher pressure (e.g. 80 atmospheres). The energy is compressed air is converted into mechanical motion (rotational or linear depending on application). A compressor or pump is used to produce the compressed air. Pneumatic drives are popular in handheld power tools or dental equipment.  PNEUMATIC DRIVES Fast actuators suitable for high cycle operation Use in hazardous area without any risks (no sparking, no overheating) Operation in environments with extreme temperatures Max. torque adjustable through operation pressure Compressed air as working medium Popular for mobile and handheld applications Linear movement without the need of additional transmission elements High noise during operation Shorter lifetime compared to hydraulic or electric drives Higher operational cost due to energy used for air compression Lower accuracy of speed control Less efficient due to pressure losses and the compression in general Not economical in very low power range  ELECTRIC DRIVES Electric drives use electric motor as an actuator. The machine transforms supplied electric power into mechanical power (torque and speed). Electric motor can be either DC or AC motor whereas AC motor technology clearly dominates in new installations (except for few specific applications). Modern electric drives use motors supplied from power electronic inverters to precisely control the position, speed and/or torque. Variable speed control saves energy, improves productivity and reduces energy cost. Efficiency of the whole drive train is superior and in high power range often exceeds 95% (combined efficiency of input transformer, VFD and electric motor).  ELECTRIC DRIVES Electric drives cover the widest power range from tiny micro drives to large multi-megawatt drive systems. Also the nominal speed ranges from few revolutions per minute to high-speed drives with thousands of rpm. The motor can operate at same speed as the driven load (direct drive, gearless drive) or utilize a gear. Electric drives are usually more silent than competitive technologies and do not produce local emissions. Electric motor drives fulfil the most stringent hygienic requirements making them a perfect fit for food and beverage industry.  ELECTRIC DRIVES Operational readiness (e.g. we don't need to wait until it heats up) Widest range of power (milli to mega) and speed Easy to use (operation on push button) Adjustable motor design with various shapes and mounting options Electric actuators can be precisely controlled Cleaness of the environment (no pollution, exhaust etc) Minimal to none environmental hazards Robustness, operational safety Short time overloadability (limited through power electronics)  ELECTRIC DRIVES High torque from standstill/low speed Easy to combine with control electronics Adjustable for the load machine Low noise Minimum maintenance High efficiency Lower power density (especially in comparison with hydraulics) Potential higher complexity of variable speed drive system Demanding design for hazardous area (explosion proof) ADVANTAGES AND LIMITATIONS OF DRIVE SYSTEM ADVANTAGES AND LIMITATIONS OF DRIVE SYSTEM  ROBOT ACTUATOR : TYPES, DESIGN, WORKING & ITS APPLICATIONS What is a Robot Actuator? An actuator that is used in robots to make the wheels of the robot turn or robot arm joints turn or to open/close the gripper of the robot is known as a robot actuator. There are different types of robotic actuators are available based on the load involved. Generally, the load is associated with different factors like torque, force, accuracy, speed of operation, power consumption & precision. The working principle of a robot actuator is to change the energy into physical motion and most actuators generate linear or rotary motion.  ROBOT ACTUATOR : TYPES Types of Robotic Actuators Robotic actuators are classified into two types according to the requirements of motion like linear motion & rotational motion. For Linear Motion: There are two types of actuators used in robots for linear motion activity they are; linear actuators and solenoid actuators. Linear Actuators Linear actuators in robotics are used to push or pull the robot like move forward or backward & arm extension. This actuator’s active end is simply connected to the robot’s lever arm to activate the such motion. These actuators are used in a number of applications in the robotics industry.  ROBOT ACTUATOR : TYPES Solenoid Actuators Solenoid actuators are special-purpose linear actuators that include a solenoid latch that works on electromagnetic activity. These actuators are mainly used for controlling the motion of the robot and also perform different activities such as a start & reverse, latch, push button, etc. Solenoids are normally used in the applications of latches, valves, locks, and pushing buttons which are controlled normally by an external microcontroller.  ROBOT ACTUATOR : TYPES For Rotational Motion: There are three types of actuators used in robots for rotational motion activity they are; DC motor, servo motor, and stepper motor. DC Motor Actuators DC motor actuators are generally used for turning robotic motion. These actuators are available in different sizes with torque generation capability. Thus, it can be utilized for changing speed throughout rotating motions. By using these actuators, different activities like robotic drilling & robotic drive train motion are performed.  ROBOT ACTUATOR : TYPES Servo Actuators Servo motor actuators in robotics are mainly used to control & monitor rotating motion. These are very superior DC motors that allow 360 degrees of rotation, but, continuous revolution is not compulsory. This actuator simply allows halts throughout a rotating motion. By using this actuator, the activity like pick and place is performed. To know how a Pick N Place robot works click on the link.  ROBOT ACTUATOR : TYPES Stepper Motor Actuators Stepper motor actuators are helpful in contributing to repetitive rotating activities within robots. So these types of actuators are a combination of both DC & servo motor actuators. These stepper motor actuators are utilized in automation robots where repeatability of activity is necessary.  ROBOT ACTUATOR DESIGN We know that there are different types of actuators used in robots. Here we are going to discuss how to design a linear actuator that is used in robotics for changing rotating motion into a pull/push linear motion. So this motion can be used to slide, drop, tilt or lift materials or machines. These actuators provide clean & safe motion control that is very efficient & maintained free.  ROBOT ACTUATOR DESIGN Power The first consideration while designing a robot actuator is Power. To obtain mechanical power out, it is essential to have power in. So, the amount of mechanical power out can be defined by the load or force to be moved. Duty Cycle The duty cycle can be defined as how frequently the actuator will work & the amount of time it will use. The duty cycle is determined by the actuator’s temperature when it is in motion since power is lost throughout the heat. When all the actuators are not the same, then there is a difference within their duty cycles. One more factor is the load, which is particularly true of DC motors whereas other factors that can determine the duty cycle are loading characteristics, age & ambient temperature. Efficiency The actuator efficiency simply helps in understanding how it will work while in operation. So, the actuator’s efficiency is found by separating mechanical power generated by electrical power.  ROBOT ACTUATOR DESIGN Actuator Life There are many factors that will extend the actuator’s life are; staying in the rated duty cycle, reducing side load, and staying in the recommended voltage, force, and extreme environments. Working Robot actuators are mainly designed for ease of use & efficiency. The design of a linear robot actuator is the inclined plane that starts with a threaded lead screw. This screw provides a ramp to generate force that works along with a larger distance to move any load. The main purpose of robot actuator design is to provide pull/push motion. So, the required energy to provide the motion is manual or any energy source like electricity, fluid, or air. These actuators generally move car seats forwards & backward, open automatic doors, computer disk drives opening and closing. Robot Actuator Failure The robot actuator failure mainly occurs due to many reasons. So these actuators can experience different failures like stuck joints or locked, free-swinging joints & total or partial loss of actuation efficiency. So, these failures will affect robot behavior if the controller of the robot has not been designed with sufficient fault tolerance.  HOW TO CHOOSE AN ACTUATOR FOR YOUR ROBOT Purpose & Intended Functionality The necessary actuator type for a specified application mainly depends on the purpose of a robot as well as the intended functionality. Physical Requirements & Constraints Whenever the type of actuator is decided to use, then developers must look at the physical requirements & constraints. Because the weight & physical size of the actuator plays a key role while arranging the actuator in the robot otherwise a heavy actuator on a tiny robotic arm may cause to fail the arm in its own weight. Strength & Power Based on their particular usage, developers must ensure the strength and power of a specified actuator to perform the task. Communication Protocol The communication protocol should also be considered while selecting an actuator for the robot. Many actuators simply support communications with PWM (pulse width modulation) whereas some actuators support serial communications. Mounting Space & Options Developers should verify the mounting space obtainable in or on the robot & the mounting options given by the actuator itself. Because some types of actuators are available with separate mounting hardware that allows you to mount the unit within different orientations whereas others are available with integrated mounting points, which are  ADVANTAGES & DISADVANTGES Advantages Robot actuator advantages include the following. Less cost Its maintenance is easy. These are accurate. Easy to control. Power conversion efficiency is high. Safe & simple to operate Less noise. These are very clean & less pollution to the atmosphere. These are very easy to maintain. Robot actuator disadvantages include the following. Overheating within fixed conditions. Need special safety within flammable environments. Need good maintenance. Fluid leakage will create ecological problems. Loud & noisy. Lack of accuracy controls. These are very sensitive to vibrations.  ROBOT ACTUATOR APPLICATIONS The applications of robot actuators include the following. The actuator is a very significant component in robotics which changes the external energy into physical motion depending on the control signals. The electrical actuators in robotics are used to change the electrical energy into rotary or linear motion Actuators generate forces that robots use this force to move themselves & other objects. Actuators are associated with robotics, devices, or prosthetic arms which need to move & bend. The linear actuators within robotics change electric energy into linear motion. An actuator is responsible for controlling & moving a system or mechanism.