Since the revolutionary launch of welding robots more than 40 years ago, innovation and process improvements have continued to permeate product development focused on customer needs. In the past, it was easy to program a robot to turn an arc on and weld a simple yet short seam with many types of metal joints. However, not all components are created equal.
Over time, the need arose for smarter machines capable of delivering greater efficiency, fewer errors, less rework and lower cycle times. As a result, weld processes and robots have greatly improved, and manufacturing industries are deploying industrial robots at an exponential rate to reduce operational costs and increase profit margins.
But, the competitive nature of the industrial landscape continues to demand advancements in technology. For welding, this newfound intelligence is most commonly achieved through a variety of sensor technologies that have taken welding automation to new heights.
Rise of the sensor
The growth of industrial robot usage for high-volume productivity, especially for robotic gas metal arc welding (GMAW), has generated an uptick in enhancements from the sensor market.1 Greater capability to control welding parameters and robotic motion, along with improved fault detection and correction, is in high demand. Likewise, the automotive sector has a larger demand for force-torque sensors and vision sensors to optimize the efficiency of pick and place, assembly and other tasks.2
Seeing opportunities for corporate growth, companies in the sensor market are creating customer-driven solutions to fill process requirements. Moreover, recent advancements in semiconductor technology have propelled players in the sensor market to drop product costs, making sensors more accessible.
Companies around the world are realizing that the utilization of affordable sensor technology has the potential to significantly improve product quality, cycle time and more. So much so that global sensor technology shipments are forecast to exceed 12 million units by 2024.3
Types of sensors
Sensors, like robots, come in a variety of shapes, sizes and prices. Similarly, sensors do no good on their own and require intuitive software to function. When a sensor is linked with good software and a robot is combined with good programming, automation is achievable.
The following insight will help robot users explore a variety of sensors to gain an understanding of what may be feasible with their new or existing welding workcell.
Sensors that are used specifically for welding robot applications typically fall into four categories: touch, through-arc, laser and vision. Likewise, they have three primary functions: seam finding, seam tracking and part scanning, which can also be used for inspection.
Each function has unique advantages depending on the part and, ultimately, the end goal, which often relies heavily on the budget established. Most of these technologies can be mixed and matched, where use is not redundant and understanding of these sensor technologies – in order of cost and complexity – is often helpful for robot users looking to improve operations.
Through-wire touch sense
Touch sense, sometimes referred to as “wire touch,” is the physical touch of a welding wire from the end of the torch to detect the conductive surface of a part about to be welded. The system uses a low-voltage circuit during a low-speed search to detect the weld joint. Although there is no hardware mounted on the robot, a wire cutter and wire break for consistent and accurate sensing are required.
Touch sense can be completed through built-in features on a welding power supply designed for automation, but it has been proven to have the best speed and accuracy with a separate dedicated circuit. This process is slower than laser technologies as one must wait for the robot to physically move to the detection location and then slowly approach the spot for best accuracy (up to 120 ipm).
Best for: Finding orientation of parts with simple joints and geometries
Not recommended for: Thin materials less than 3/16 in. with small joint thickness; square butt joints; high-demand cycle times
Complexity: Low; built-in pendant commands
Cost: Low
Through-arc seam tracking
Innovative through-the-arc seam trackers have the ability to use a solid-state sensor mounted near the welding power supply to actively measure arc characteristics during a weld to determine variations between the robot’s taught path and the actual seam path.
The function applies minor corrections to amend the programmed path to follow the physical seam during welding. Welding speed is regulated to a moderate 50 ipm. Return on investment (ROI) with this technology is generally much lower than modifying and re-engineering parts and fixture tooling in such a way that it eliminates all potential seam variation.
Best for: Parts with long or curved seams with some variation from part to part
Not recommended for: Thin material less than 0.12 in. or non-weaving weldments; large gaps; weldments less than 6 in. or requiring greater than 50 ipm travel speed
Complexity: Low; prewritten programs and algorithms provide smooth and easy operation
Cost: Low
Laser sensing
A non-contact laser sensor is an option to “touch sensing” that is two to five times faster as most of the robotic motion required is eliminated to acquire the part location. Instead of a physical wire touch to a part, a laser dot and sensor capture the location and orientation of a part as quickly as the laser fires.
While it is still easy to teach, it requires a torch-mounted sensor. And, like touch sense, the laser sensor cannot find square butt joints and can potentially run into issues with highly reflective surfaces. However, it eliminates the need for a wire cutter and wire break, and it can detect lap joints down to 1/16 in. thick.
This system also requires a torch-mounted laser that could limit torch access in some tight areas on the weldment. Select laser sensing solutions can work with any welding power supply. A company’s investment when upgrading to this technology equates to about $20 per workday over a year, but an allowance for an additional 26 cycles per shift (based on a 90-sec. cycle time) should be made, when compared to touch sensing technologies. High-output facilities commonly realize ROI in less than one month.
Best for: Faster cycle times without breaking the budget
Not recommended for: Square butt joints; larger or inconsistent gaps; highly reflective cut or polished materials; weldments with limited joint access
Complexity: Low-medium; some basic user training required with built-in commands
Cost: Medium
2-D camera
Camera systems, such as Cognex, allow a robot user to capture the location of a part in merely second with a camera sensor mounted to the arm of the robot. Not only does this system find the location of the part, it also quickly confirms orientation without adding many extra test points as required with touch or laser sensing.
Because the unit is grabbing a wider image, it can also be used to ID the fixture being used and prevent called job errors. As a downside, it is more sensitive to lighting and surface conditions. It also does not provide depth of field, so stacked parts can be more difficult to program.
As a bonus, this camera can even be used to verify tool center point (TCP) for quick realignment. ROI goes up a little in time due to the custom programming required, but proper use often enables automation that would have been previously impossible or more expensive.
Best for: Parts with higher variability on placement and very demanding cycle times
Not recommended for: Applications with large variations in depth, lighting or material surface conditions
Complexity: High; additional user training required
Cost: Medium-high
Laser seam tracking
When the latest-technology laser sensors are combined with high-speed controllers, seam and part locations can be processed in real time. Like through-arc solutions, a dedicated program compensates path and even adapts welding parameters for seam location and variation.
Specialized products reliably track thin gauge metals and allow simultaneous welding two times faster than through-arc tracking at up to 100 ipm. This allows automation in parts that inherently have changing gaps, such as welding around larger cylinders. Like laser sensing hardware, this also requires a box that may limit the torch access in tight areas of the weldment.
This sensor is also used for weld inspection when coupled with a proper data tracking system. Weld inspection and traceability is quickly becoming an industry standard for automotive and safety critical welds. Arc data from the power supply is combined with individual scans of the weld to track each part that comes through production. ROI here comes as a figurative insurance policy that can reduce widespread part recalls and the weighty liability that comes with any potential part failure.
Best for: Thin materials with varying seams that demand the fastest potential cycle time
Not recommended for: Extremely wide gaps or parts with limited access to joints, parts and tooling with limited access
Complexity: High; additional advanced user training required
Cost: High
3-D camera
Often times, 3-D imaging solutions are used for complex bin picking automation. This is not a typical sensor for applications merely welding the same part and orientation. This solution enables the use of a material handling robot to pick up a part, place it into tooling, weld using a welding robot and then remove the part for a completely automated process. With this type of technology, all factors of complexity and cost increase from the other solutions.
Best for: Randomly placed parts and “lights out” automation when placing them in a fixture
Not recommended for: Simpler jobs that can be conquered more economically
Complexity: Very high; additional advanced user training required
Cost: Very high
Sensors make sense
Sensor technology has come a long way in the recent past, providing game-changing advantages for end users spanning diverse industries. From industrial welding robots to human collaborative robots (cobots), sensor technology improvements are helping companies handle the diversity of applications required, especially where robotic welding is concerned. Even 3-D scanning and modeling sensors that have been developed for inspection are being researched for one-off weld automated programming to open yet another generation of innovative solutions.
So, when do sensors make sense? If one has a redundant part with variations that tooling and part consistency or design cannot resolve, there is a sensor that can. Keeping that in mind, expectations for ROI should be set with clear-cut goals associated with the investment, such as reduced waste, improved quality, less downtime and improved production.
While the initial cost of robotic implementation may seem overwhelming to some manufacturers, understanding the cost savings associated with a long-term approach to automation – and subsequent technologies, like sensors – is essential.
ROI is usually realized quickly aside from sticker shock and should be discussed in more detail with an integrator. Moreover, education about the different types of sensors (and their capabilities) available for advanced robotic welding solutions makes it easier for manufacturers to tackle the most difficult, dangerous and dirty tasks, leading to higher production, better quality and ultimately increased profitability.
1. Robotic arc welding sensors and programming in industrial applications, International Journal of Mechanical and Materials Engineering, December 2015
2. Robot Sensor Market Outlook – Industry Size, Share Report 2018-2024, Global Market Insights, 2018
3. Robot Sensor Market Outlook – Industry Size, Share Report 2018-2024, Global Market Insights, 2018
