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Understanding Robotic Arm Basics: Axes and Motors

Before we can get into programming a robot arm, a few things must be explained first.  Robots' arms are defined by the number of axes used, whereby each axis may have one or more servo motors to control its movement.  Today, most robot arms are either five or six-axis; however, it's important to note that a six-axis robot can maneuver and turn along all axes.  The JMOR Connection Inc will explain how a robot's motors allow it to move and the different methods to program a robot arm. 

Servo Motors: Powering Precision and Flexibility in Robotic Arms

Today, robots use a servo motor, consisting of a motor, control circuit, and sensor that can determine its speed and exact current position. There are two types of servo motors: AC, which is powered by electricity and operates because of voltage and frequency.  Most industrial applications often use AC Motors because they can handle large surges.  DC Servo Motors can work because of voltage only.  Servo Motors are used because they have a lower weight, which gives the robot arm more flexibility and the ability to balance more quickly.  Servo Motors have also been chosen since their precise movements allow them to operate within tight tolerance specifications.

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Configuring Robotic Arm Axes: Setting and Preserving Home Positions

When robot arms are delivered from the manufacturer, each axis must be configured to an absolute or starting position.  The value the user sets on each axis for the servo will be stored on an encoder for that motor and uses batteries to hold these settings if power is lost.  However, it is vital that if you should get a warning to change your encoder batteries, remember to change them while the power is on, or your servo home positions will be lost.

Choosing the Right Robot Arm for Your Application: SCARA and More

One of the most critical tasks is understanding the task needed and seeing which type of robot arm will best fit your application.  There is SCARA (Selective Compliance Articulated Robot Arm), a kind of industrial robot used for pick-and-place or assembly operations quickly with precise accuracy.  While these robots are incredibly efficient, they are often limited by the weight or payload they can manage. Did you know that SCARA Robots can operate within tolerance ranges of less than 10 microns as opposed to 20 microns for the six-axis robot?

Six-Axis Robots: Versatile Solutions for Industrial Manufacturing

Six-axis robots are more suited for industrial manufacturing, where there is a greater need for flexibility, strength, and reach.  Some applications that use six-axis robots are automated welding, material handling, material removal, painting, and automated plastic injection molding.  These robots can rotate, bend, move in an arc, and grip objects at different angles.  Since they have 6-axis free movement, objects can be rotated or tilted, making them more suitable for advanced pick-and-place applications.

Delta Robots: Precision and Speed in Assembly and Packaging

Delta robots are another type, and they have a base that is connected to each joint parallelogram.  It consists of a base platform with three actuating arms attached to a pair of arms to form a passive arm.  Each passive arm connects to a traveling platform and utilizes three axes for freedom in three directions.  Delta robots are best suited for assembly, dispensing, pick and place, material handling, part transfers, and robotic packaging applications.  Those wanting to use a Delta robot must ensure that the part is lightweight and is a standard shape as it operates at fast speeds.

Teach Pendant Programming: The Common Method for Robot Arm Control

Robot Controllers that talk to the robot arm may be programmed in three ways:  teach, lead, and offline.  The teach method is the most common, as over 90% of all industrial robots are programmed this way and taught positional location.  A robust keypad and set of controlls to program is called a teach pendant and is hardwired into the robot controller. Before using a teach pendant to program the robot arm, one must understand how the deadman switch and the on/off programming switch operate on the back of it. 

Teach Pendant Safety and Basic Operation

First, the switch needs to be turned on to allow programming with the teach pendant. Next, the deadman's switch, also called an enable switch, is usually a pair of long buttons on the back of the teach pendant with three possible states:  position 1:  off, position 2:  on, and position 3:  off needs to be in position 2. The idea was to stop the robot from moving if either one of two buttons was not pressed or pressed to stern as a safety. Thus, to begin the program, the operator must keep the deadman’s switch in position two, pressing it lightly for the first click and touching the appropriate button to cause the robot to move.  The axis has to be selected, and you need to move the robot arm to each point you want, save it, select another point, and change the axis.  The operator does this while watching the robot and verifying it is at the correct net position or point.

Lead-Through Programming: Guiding Robot Movements with Precision

Another method for programming a robot arm is the lead-through method, where the operator moves the robot in the positions he/she wants it to take.  This method is often used with welding and spray paint operations and does not require experienced programmers but only skilled tradespeople.  Lead-through programming allows the controller to record each motion path as the operator guides the robot, taking less time than teach pendant programming.

IDE Programming for Robot Arms: Seamless Development and Testing

Robot Arms can be programmed in an IDE (integrated developer environment) where the programmer can choose the robot they want, create their programming by dragging or dropping, or typing in specific functions such as C, C+, Python, etc.  This environment is a great way to design a program without taking the robot offline; however, it still needs to be tested to ensure it functions as it did in the virtual environment.

Autonomous Robot Programming for Welding

Latest advanced robots support another type of programming called autonomous; thus, in welding, the user must upload a 3D model of the object, set the welding parameters, and figure out the correct paths and points to be at automatically.  These robots use computer-aided vision to detect the object and adjust if any deviations are found.

Understanding Robot Vision and Coordinate Systems

The programmer must understand how the robot sees things, whether the teach pendant or the offline method is chosen.  In the IDE, we create a station where we can select the robot type we want, 2,3,4,6 axis, or other robot specifications.  The robot can see the world as a world, local view, or tool view, but what do they each mean?  The worldview causes the robot to see things from the base of itself.  The local view allows the robot to see things from the object’s perspective, and the tool view allows the robot to be moved regarding the end of its tool.   Robots have three primary coordinates that can be utilized:  X : (rolling) rotates the tool on its center axis Y, (pitching) moves the tool vertically; Z:  (yawing) turns the tool left/right, each using having two numbers to identify the specific location.

Robot Motion Types and Instruction Codes

When we move a robot’s joint or axis, it can be done with a motion of either joint, linear or circular.  The instruction code will start with either a J, L, or C, and next, a P[1] for a local point, PR[1] to indicate a global position register.  The next part of the instruction is for the speed; if it’s a joint, it will have a percentage; for linear, the speed will be mm/s.  Finally, we need to specify the termination type, FINE or CNT.  Fine will move smoothly using to the end point while CNT will cause the robot to have jerky stop.

Sometimes, you may want to add ACCxx to indicate that you wish the acceleration to be faster or slower as the robot starts the particular movement.

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Understanding Joint, Linear, and Circular Movements in Robots

Joint movement type will quickly move from point a to b in the fastest possible.  The robot will only move in a straight line when talking about linear movement.  A movement type called a circle will also move in half circles. Robots today can also have seven axes as they need another freedom to move through the assembly line to the next operation.

Programming Robots: Mastering Coordination and Degrees of Freedom

Robots can be easily programmed in various ways; however, the key to understanding is how you see it so that it can be translated into instructions it may use to move and perform its operations.  Each axis from one to six allows one degree of freedom in which a robot may move.  Many robots will have a seventh axis, which enables the robot to be able to move up and down an assembly line in a production environment.  Remember, as I discussed earlier, you have to know how to proceed, select a coordinate system, and then program those points into instruction commands.

Remember, mastery comes with practice and continuous learning. As you dive deeper into robotics, you'll encounter new challenges, ideas, and innovations. Embrace them with open arms—robotic arms, that is—and keep refining your craft.

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