Drives & Controls May 2022

46 n LINEAR MOTION May 2022 www.drivesncontrols.com Choosing and using single-axis robots I ndustrial robots boost productivity. And since the pandemic, it has become clear that they can safeguard workers’health by reducing shopfloor staffing and human contact with components and assemblies. Single-axis robots are easy to understand and use and are already automating a variety of tasks, sometimes by themselves, but often configured into groups co-ordinated by a central controller. They generally bring greater throughput, repeatability and consistency to operations. System integrators can develop systems based on single-axis robots in one, two or three axes to tackle handling and assembly challenges. Applications can include transferring bulk items into individual trays or pallets, performing sequences such as feeding and cutting, and positioning jigs and tools. Two or more linear devices can work together to perform tasks that demand high accuracy, such as laser cutting, painting or dispensing. Custommulti-axis cartesian robots can be built by combining single-axis robots for each axis. In situations requiring multiple axes, linear devices can act in concert with Cartesian robots, connected to the same controller which can control one or more additional single-axis robots working as part of a coordinated system. This gives the flexibility to expand the system if needed. What to look for Rigidity is one of the most important properties of a single-axis robot to ensure precise and repeatable positioning and allow the slider to move freely with minimal friction. It allows associated mountings and supports to be simplified, saving space and costs. Using advanced design techniques, it is possible to save space at the same time as increasing rigidity on every axis. The latest high-rigidity single-axis robots have a one-piece construction and built-in linear guides, increasing their rigidity by up to 300% while reducing rail widths. They have reduced heights with lower centres of gravity, enhancing performance when used as the x- axis of a custom-built cartesian robot. When choosing a single-axis robot, you should need to consider the type of motor used to drive the axis. Some are supplied without motors, allowing standard motors to be fitted. Attachment kits allow the motor to be oriented to suit the application. Some robots have ground ballscrews designed for use with servomotors. Stepper motors can provide a cost-effective alternative, with similar functions to a servomotor for applications with lower payloads where ultimate speed is not vital. The latest models can handle payloads almost four times bigger than their predecessors, and excursion speeds of 1.2m/s – or 20% faster than before. For applications transporting lightweight workpieces over long distances at high speeds, linear-motor-driven single-axis robots can be cost-effective. These are available with strokes of more than 4m, top speeds of 2.5m/s, and repeated positioning accuracies of ±5μm. The cycle time savings can be significant, while linear motors are also quiet and suffer minimal wear. Their payload capacities are typically a few kilograms. When evaluating single-axis robots for multi-axis applications, simulation and analysis tools can ease set-up and long-term maintenance. For example, Yamaha has aWeb- based simulator that helps users to choose the optimum specification. They can quickly calculate important criteria such as projected cycle times and ballscrew lifetimes. There are also PC applications that work with the robot controllers to assist with analysis and fine-tuning. Users enter details of the usage conditions – such as transport mass, point data and operation type – and the software assesses the performance in a virtual environment without running real hardware. These simulations can predict total operating times, time for individual operations, maximum speeds, acceleration and so on. This software can also provide real-time tracing of actual speeds, motor loads, and the time taken to reach specific positions. Alarm histories can be checked to analyse errors and to help identify the root cause of problems. It is possible to analyse status up to the point that an error occurred, helping to identify issues such as overloaded motors. To summarise, single-axis robots can provide an effective foundation for integrating automated processes. Their advantages include easy selection, design and use. n Industrial robots can be as simple as a single axis for basic transport and positioning, or can be scaled up to multiple axes working in concert. As Oumayma Grad fromYamaha Robotics explains, the latest single-axis models bring together advanced functions and software tools to enhance accuracy, speed, and ease of use. Single-axis robots can be configured to operate as customised Cartesian robots.