DWFritz Automation Inc. builds sophisticated, custom automation equipment. Capabilities include robotics; machine vision; high precision, high speed assembly; and automated inspection. A medical-technology customer challenged the firm to create a system using high-performance machine vision, a high-precision, six-axis robot, and sophisticated software that would enable high-throughput inspection of many types of medical implants and small parts, while lowering manufacturing costs. Other primary objectives were to ensure NIST measurement traceability and comply with Food and Drug Administration (FDA) regulations.

Maximum flexibility was a driving force in the concept. The system had to allow thousands of recipes to be programmed by the manufacturer, which currently has more than 600. Most importantly, the fast-growing medical company needed to gain more control over its complex manufacturing process. The system feeds measurements automatically and electronically into the company’s statistical quality management system.

Previously, there was considerable human intervention in the customer’s operation, plus extensive use of go/no-go gauges, micrometers, optical comparators, and video measuring equipment. All that measuring equipment needed to be calibrated and maintained, leading to significant recurring cost. Human inspectors had great difficulty obtaining repeatable results, especially with challenging external measurements, such as radius.

The integrator designed a custom system incorporating a Denso six-axis robot, two high-performance, high-resolution Cognex smart cameras with telecentric lenses made by Edmund Optics, custom end-effectors, and an industrial PC running Cognex’ VisionPro machine-vision software.

The robot picks parts up individually from trays containing 25-100 units and positions each before the cameras. The system then measures up to 55 dimensions on each part with micron-level repeatability. If the parts meet the customer’s stringent quality requirements, they are returned to the tray. If not, the robot places them in a reject tray for subsequent analysis.

The system has throughput of better than one part per second, on average, with repeatability better than two microns, depending on the parts’ features. Automated calibration and verification for the robot and vision system, along with NIST traceable accuracy, means the medical company can focus on optimizing its manufacturing process for higher yields. Since the system can be calibrated with the same vision tools, the customer can run multiple systems on the production floor with excellent system-to-system repeatability.

Machine vision can be used to set up a sophisticated workcell-safety system with warning and shutdown areas.

Unauthorized human activity is one of the most common causes of machine-safety system failures.

For example, poorly designed safety systems often make maintenance and repair activities difficult or impossible. After attempting to work within poorly designed safety-system constraints, workers may disable the safety system to complete their tasks more efficiently. The safety system is therefore disabled just when it’s most needed. Resulting accidents and injuries then count as safety-system failures.

This vision-based safety system allows users to define warning and shutdown zones through a computerized user interface. When a warning zone is breached, a controller provides visual and audible warnings to workers and sends a signal to the machine-control system to slow the equipment to a “safe speed.”

Safe-speed systems constrain machine movements to speeds slow enough for humans to escape accidental collisions. Humans can react within about a quarter second to perceived danger from moving equipment. Machine structures should move slowly enough so that a human working in close proximity can see the movement, search his or her surroundings for a safe exit, and get out of the way before being struck.

If the person or object (such as an automated forklift) enters a shutdown zone, the system sends a signal to halt the machinery. Warning and shutdown signals are sent within milliseconds of an intrusion, fast enough to prevent accidents and equipment damage. Once shut down, machinery can’t be restarted until the detection zone is clear of unauthorized objects and people.

The company’s 3D detection technology triangulates images from four smart cameras to identify objects and people moving in and around the work zone, distinguishing between one, two, or more targets, with real-time tracking of all targets within the system’s field of view.

Mounted high above the machinery, the imagers can view multiple potentially dangerous areas of human and machine interaction, and are tamper-resistant.

By combining cues based on object size, shape, and movement, the detection system can distinguish between targets representing potential safety issues, and unimportant background objects. Ignoring background objects avoids nuisance alarms, which is another major cause of safety-system failures.

The company says its system is designed for user flexibility. During initial installation, plug-and-go harnesses enable simple imager installation, wiring, and even relocation of imagers when necessary. Reconfiguring the system is simple via a Microsoft-Windows-based PC interface. Warning and shutdown zones can be quickly redrawn with the click and drag of a mouse.

When mounted 11 ft above the floor, one imager can protect a zone measuring up to 8 ft x 10 ft. Up to 10 imagers, creating 10 protection zones, can be managed by a single controller monitoring up to 800 sq ft. Smart camera technology, which makes it possible to distribute image processing work where it’s needed, makes the system feasible.