1. Safety Requirement in Robotic Welding Cell
INTRODUCTION
Automating the torch motions decreases the error potential which means decreased scrap and rework. With robot welding you can also get an increased output. Not only does a robot work faster, the fact that a fully equipped and optimized robot cell can run for 24 hours a day, 365 days a year without breaks makes it more efficient than a manual weld cell.
1. SAFETY REQUIREMENT IN ROBOTIC WELDING CELL
SAFETY STANDARDS FOR ROBOTIC WELDING
- Specification for Arc Welding Safety
- Guide for Components of Robotic and Automatic Arc Welding Installations
- Risk Assessment Guide for Robotic Welding
Welding is an established manufacturing process with known potential hazards. Potential safety hazards associated with arc welding include arc radiation, air contamination, electrical shock, fire and explosion, compressed gases, and other hazards. Robots were originally designed to perform the job functions of a human. Robots can replace humans in the performance of dangerous jobs and are considered beneficial for preventing industrial accidents. On the other hand, robots have caused fatal accidents.
One of the best solutions for robot safety is to purchase a complete welding cell from a robotic integrator . A complete cell includes barriers, all necessary safety devices, and a method of loading and unloading the workstation.
Each robot installation must be carefully planned from safety view point to eliminate hazards. When the robot is in operation it is necessary that people remain outside the work envelope. Barriers or fences should be in place around the robot. All doors and maintenance openings must be protected by safety switches, and the weld areas must be safe guarded so that the power is immediately removed from the robot when a door is opened. Emergency stop buttons should be placed on all operator panels, robot cabinets and robot programming panels. Barriers be designed to completely surround the robot and eliminate the possibility of people climbing over or under to get inside the barrier. Signal lights must be arranged on the robot or in the robot area to indicate that the robot is powered.
This project expect systems integrators to conduct a risk analysis and then design and adjust systems for the safest operation that meets or exceeds all plant, federal, state and local codes. These safety measures include fence barriers, gate interlocks, floor safety switch mats, photo-cell and light curtains, fixed guards, emergency stop hardware and software, as well as frames and screens to protect workers from welding arc flash.
2. APPROPRIATE PROTECTIVE DEVICES
Another asset a systems integrator can offer is access to multiple equipment options and configurations that ultimately lead to better productivity. Some integrators offer pre-engineered or standard work cells. These systems provide out-of-the-box affordability, but are not always the right solution when customization is required. Integrators with flexible, modifiable work cells can provide a cost-effective solution tailored to the application.
Robotic system
- Position
The positioner determines how the part is presented to the robot for welding. Typical positioner types include stationary tables, turntables, headstocks, tailstocks and Ferris wheel types.
- Fixtures
These hold the part to proper tolerances for welding. Unique to each automation project, fixtures are only as good as the quality and innovation the systems integrator puts into them. When selecting a robot, the integrator considers accuracy, speed, reach, operator interface and the various options available with each robot.
- Base Platform
A common base platform, which the systems integrator designs and constructs, connects all components. It is also a base for controls, flash screens, barriers and safety components.
- Operator Interface
This is the final component of the work cell. Simple push buttons, or a touch-screen panel, are often recommended interfaces
Technician
This is important methods for ensuring worker safety is adequate training conducted by the systems integrator. A hands-on, mentoring approach works well with employees in the welding industry who are comfortable working with their hands. While some formal classroom training is needed, the majority of the teaching should be done on the equipment when it is set up at the systems integrator's facility.
Training levels vary in what the integrator provides. There is basic operation training for work cell and robot operation, and advanced training for robot programming, maintenance training and welding training.
The industry standard is one week for each of the training courses. The ideal learning environment is a class tailored to the specific needs of each trainee along with one-on-one interaction with the instructor/mentor. Retraining, introduction to new techniques and refresher courses are other benefits systems integrators offer customers.
3. ROBOTIC WELDING CELL SAFETY BARRIER SYSTEM
Three types of safeguarding devices that can be used as part of a comprehensive safety system for robotic welding setups.
- Safety light screens
- safety interlock switches
- two-hand controls
Safety light screens
A light screen is an optoelectronic device used to protect welders from a machine hazard. The basic elements of a safety light screen, or safety light curtain, are an LED emitter array and corresponding phototransistor receiver. They produce a "screen of light" with a specified resolution that detects intrusions into the sensing field. When a object such as an arm or hand is detected, it generates a stop signal to the machine control. This sensing field is installed between the hazard and personnel, at a distance from the hazard such that an individual cannot access the hazard.
Interlock switch
Safety interlock switches monitor the position of a guard or gate, and they are used to shut off power, control personnel access, and prevent the machine from starting when the guard is open. While hard guarding includes fixed and adjustable guards, safety interlock switches can be used with interlocked guards.
Interlocking guards (such as doors, gates, and covers) can be moved and often are used when frequent access within the guard is needed. Guards that can be moved or removed generally need to be interlocked, preventing an accident from occurring if someone tries to access a guarded area.
A movable interlocked guard is recommended if operators need intermittent to frequent access to a hazardous area. If the guard is moved or opened, the interlock switches prevent cycle initiation or send a stop signal to the machine control. By locking the guard closed or in position, some interlock switches can also prevent access to the machine until it comes to a safe stop, maximizing safety by further protecting operators from potential injuries.
two-hand controls
Two-hand control systems comprised of two actuating buttons (or hand controls) and a safety module are used to activate a machine and prevent false or unintended cycles. When both buttons are concurrently actuated within ½ second, via mechanically based buttons or ergonomically designed buttons, a signal is sent to initiate and control a machine cycle.
Along with preventing unintentional machine actuation, two-hand controls can function as a safeguarding device by physically engaging both of an operator's hands, keeping them out of harm's way when a machine is operating. If an operator releases one or both actuating buttons, the safety module (or other logic device) immediately stops the machine cycle.