12 things to pay attention to when buying a packaging robot
It’s not always easy for managers and engineers to find a common language. Industrial solutions are a complicated topic and it is only natural to feel lost if this subject is new to you. The communication has a crucial role in the cooperation between engineers and their clients, which is why we always strive to inform and educate our clients, in order for them to make the right choice. This is particularly important if you are about to invest in some kind of robotic equipment, whether it is a robotic palletizer or some other modular robotic add-on for your packaging line. Since we want to help you make the right choice, we decided to post this short guide on defining parameters of industrial robots, so that you can gain a better understanding of technical descriptions and specifications of each robotic arm. There are a lot of parameters used to describe the features and possibilities of a robot and here are the most important ones.
- Number of axes or Degrees of freedom: Two axes are needed for a robotic arm to reach any point in a plane. To reach any point in space – three axes are a must. To have the full control of the orientation of the end of the arm, and to enable the wrist rotation, three more axes are required. These additional axes are called yaw, pitch, and roll, and these terms were originally used in aviation. Sometimes, engineers chose to trade the number of axes in exchange for accuracy, speed, and cost. The SCARA robot with 4 axes is an example of that.
- The working envelope refers to the region of space a robot can reach.
- Kinematics refers to the way rigid parts and joints in the robot are put together. This determines the robot’s possible motions. According to kinematics, robots can be classified as articulated, Cartesian, parallel and SCARA robots.
- Carrying capacity or payload refers to how much weight can be lifted by a robot.
- Speed refers to how fast the robot can position the end of its arm. This may be determined in terms of the linear or angular speed of each axis or as the speed of the end of the arm when all axes are in motion.
- Acceleration is a measure connected to how quickly an axis can accelerate. Acceleration can be limited by distance and movement pattern: a robot may not be able to reach its maximum speed on short distances or on complex paths that require frequent changes of direction.
- Accuracy refers to how closely a robot can reach a specified position. This measure is calculated by comparing the actual position of the robot with the commanded position. The error between these two is a measure of accuracy. A vision system, Infra Red, or other external sensors can improve accuracy. The working envelope and a payload can also affect accuracy.
- Repeatability is a measure that refers to how well will the robot return to a programmed position. This is not the same as accuracy. When the robot is told to go to a certain X-Y-Z position, and the robot gets to a position that is one 1 mm away from the required position – that one-millimeter error is the measure of accuracy which can be improved by calibration. But if that position is stored in a robot’s memory and each time when the robot is sent there it returns to within 0.1mm of the required position – then the repeatability will be within 0.1mm.
Repeatability is the main criterion for a robot and it is not the same in different parts of the working envelope. It also changes with the speed and payload. ISO 9283 demands that accuracy and repeatability should be measured at highest speed and at heaviest payload, but these results aren’t the best indicators of robot’s possibilities since the robot could be much more accurate and repeatable at lighter loads and smaller speeds.
- Motion control refers to the level of control required for some tasks. Simple pick-and-place assembly, typical for robotic palletizing, requires for the robot to merely return repeatedly to a limited number of pre-taught positions. For more complex applications, like welding and spray painting, the motion must be constantly controlled.
- Power source: Some robots utilize electric motors, some utilize hydraulic actuators. Electric robots are better in the terms of speed, hydraulic robots are better in term of strength and precision in more complex applications such as spray painting.
- Drive: some robots connect electric motors to the joints via gears; others connect the motor to the joint directly (direct drive). Using gears causes measurable ‘backlash’ (loss of motion in a mechanism caused by gaps between the parts). Smaller robotic arms often work at high speed, low torque DC motors. These motors generally require high gearing ratios which have the disadvantage of backlash. In such cases, the harmonic drive is often used.
- Compliance is a parameter linked to an angle or distance at what robot axis will move when a force is applied to it. Compliance causes that when a robot goes to a position carrying its maximum payload, it’s final position will be slightly lower than the position when it is carrying no payload. Compliance can also be responsible for overshoot when carrying high payloads in which case acceleration would need to be reduced.
We hope you got to know our mechanical friends better. Wisely chosen robotic packaging equipment, acquired from the right manufacturers and integrated by the right experts can bring significant efficiency improvements. To learn more about the way we utilize robots, check out our Tetristack Robotic Palletizers, available in 6 different variations created to respond to your particular needs.