Press Brake Safeguarding Basics

Press Brakes are currently a hot topic in the “Machine Safeguarding” arena. OSHA regulations consider press brakes to be a 1910.212 machine, saying to the employer; “one or more methods of machine guarding shall be provided to protect the operator and other employees in the machine area from hazards such as those created by point of operation, in-going nip points, rotating parts, flying chips, and sparks” … 1910.212 requirements are good place to start, but they leave out the details of exactly how to go about safeguarding any particular machine. Therefore, a reference to an ANSI Standard like B11.3 on press brakes is often used to identify specific safeguarding alternatives. ANSI B11.3 may however need some help from ANSI B11.19 on safeguarding methods, to provide a complete picture of how to go about protecting people.

Older press brakes, like those manufactured in the mid-1980’s and before, were mechanical (flywheel-type) machines, some of which are still in use today. Because the stopping times on mechanical press brakes are long, equally long light curtain safety-distances result, making that safeguarding device impractical in many cases.

Press brakes manufactured after the mid-1980’s are much more likely to be hydraulic. Hydraulic press brakes allow for a wider variety of safeguarding options than mechanical press brakes do, and offer faster stopping-times, resulting in closer safety-distances where light curtains or two-hand controls are used.

A common method of safeguarding press brakes is with a vertically mounted infra-red light curtain. Hydraulic press brakes allow for short stopping times so that a light curtain can be mounted relatively close to the dies.

Two-hand controls on press brakes are often used in the sequence-mode of operation where the actuators bring the machine down and stop before the dies close, allowing just enough die-space to feed the part. The part is placed in the remaining die-opening, then a foot-switch is used to make the bend and return the machine to its full-open position.

Safety distance is required for both light curtains, and two-hand controls. That distance must be calculated with a stop-time measurement (STM) device on a quarterly basis. STM readings must be documented to show safety inspectors.

ANSI B11.3 which was updated in 2012, offers two completely new categories of protection for hydraulic press brakes: Active Optical Protective Devices (lasers) and Safe Speed Safeguarding. Active Optical Protective Devices (AOPDs) detect hands and fingers in a danger area. The biggest attraction for AOPDs are for jobs where the operator must hand hold small parts up close to the dies. A unique feature of AOPDs is that that they are designed to be mounted with zero safety distance, unlike light curtains that must be mounted at a calculated safety-distance, as outlined in ANSI B11.3. Safe Speed Safeguarding is based on a ram speed of 10mm per second or less, providing that speed is carefully monitored. Again, these two new methods of protection can only be applied to hydraulic press brakes (and potentially Servo-Drive Press Brakes).

The Lazersafe® Sentinel Plus is the most advanced guarding solution available designed specifically for hydraulic press brakes. The Lazersafe ties directly into the machine’s existing hydraulic and electric control circuits, providing a Category 4 solution. The Lazersafe is CE rated and allows machine operators to hold workpieces within 20mm of the point of operation. Encoder feedback ensures that the speed and position of the tooling is continuously monitored, and a 4.3” HMI provides machine operators immediate feedback of all vital functions. The Lazersafe Sentinel Plus is compatible with a wide variety of machines and tooling types, material thickness and easily allows for box shapes to be formed.

The backs of press brakes cannot be left wide open. Two hazards exist often exist here. The first is reaching the dies from the back. The second is the possibility of a multi-axis back gauge moving and creating pinch points. As to exactly what is required on the back of equipment often depends on local OSHA interpretation. The very least, an awareness barrier, like a railing, chain, or cable with a “Danger” or “Warning” sign, complete with Pictograms, not just verbiage. (see photo)

For local OSHA interpretations that won’t accept awareness barriers, a full perimeter guard may be the answer for the back of a press brake. That guard can either be bolted into position, or if it’s movable, an electrical interlock switch can be installed to make sure it stays closed.

As with any industrial machine, Lockout/Tagout on Press Brakes must strive for “Zero Energy State” to and within each piece of equipment using both locks and tags.

Also mentioned in the ANSI standard is die safety blocks; please see our related blog post on “Demystifying Die Safety Blocks”.

Please call 1-800-922-7533 or visit rockfordsystems.com for more information.

Playing It Safe With Robotics

OVERVIEW

Robotics is a growing field as more and more companies are incorporating industrial automation into their production processes. In just the first nine months of 2016, 23,985 robots were ordered from North American companies, many of which require machine guarding equipment to maximize productivity and safety. Robots are used for replacing humans who were performing unsafe, hazardous, highly repetitive, and unpleasant tasks. They are utilized to accomplish many different types of application functions such as material handling, assembly, arc welding, resistance welding, machine tool load/unload functions, painting/spraying, etc.

POTENTIAL HAZARDS
Studies indicate that many robot injuries occurring in robotic automation typically occur during non-routine operating conditions, such as programming, maintenance, repair, testing, setup, or adjustment when the worker may temporarily be within the robot’s working envelope.

Non-Safeguarded Robots
Non-Safeguarded Robots

As stated by OSHA, mechanical hazards might include workers colliding with equipment, being crushed, or trapped by equipment, or being injured by falling equipment components. For example, a worker could collide with the robot’s arm or peripheral equipment as a result of unpredictable movements, component malfunctions, or random program changes. The worker could be injured by being trapped between the robot’s arm and other peripheral equipment or being crushed by peripheral equipment as a result of being impacted by the robot into this equipment.

Mechanical hazards also can result from the mechanical failure of components associated with the robot or its power source, drive components, tooling or end-effector, and/or peripheral equipment. The failure of gripper mechanisms with resultant release of parts, or the failure of end-effector power tools such as grinding wheels, buffing wheels, deburring tools, power screwdrivers, and nut runners are a few of the possibilities.

Non-Safeguarded Robot
Non-Safeguarded Robot

Human errors can result in hazards both to personnel and equipment. Errors in programming, interfacing peripheral equipment, connecting input/output sensors, can all result in unpredictable movement or action by the robot which can result in personnel injury or equipment breakage.

Human errors in judgment frequently result from incorrectly activating the teach pendant or control panel. The greatest human judgment error results from becoming so familiar with the robot’s redundant motions that personnel are too trusting in assuming the nature of these motions and place themselves in hazardous positions while programming or performing maintenance within the robot’s work envelope.

SAFEGUARDING AUTOMATION CELLS

Robots in the workplace are generally associated with the machine tools or process equipment. Robots are machines, and as such, must be safeguarded in ways similar to those presented for any hazardous remotely controlled machine, falling under the general duty clause or OSHA 1910.212(a)(1) or 1910.212(a)(3)ii.  Refer to https://www.osha.gov/SLTC/robotics/standards.html and OSHA’s compliance directive on robotics STD 01-12-002 at https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=DIRECTIVES&p_id=170 for more information.

Robotics Packaging Cell Courtesy: Banner Engineering
Robotics Packaging Cell
Courtesy: Banner Engineering

Various techniques are available to prevent employee exposure to the hazards which can be imposed by robots. The most common technique is through the installation of perimeter guarding with interlocked gates. A critical parameter relates to the manner in which the interlocks function. Of major concern is whether the computer program, control circuit, or the primary power circuit, is interrupted when an interlock is activated. The various industry standards should be investigated for guidance; however, it is generally accepted that the primary motor power to the robot should be interrupted by the interlock.

Although ANSI standards are guidelines, many U.S. industry experts experts agree that ANSI standards provide the best guidelines for safeguarding machinery that doesn’t have a vertical OSHA requirement.
ANSI/RIA R15.06-2012 is the most recent U.S. Standard on Industrial Robots, which requires that perimeter guards contain the robot automation. These guards are required to have a 12-inch sweep and a 60-inch height (ANSI/RIA R15.06-1999). However, CSA 2003 cite best practices at a 6-inch (.15m) sweep and a 72-inch (1.8m) height.

When a robot is to be used in a workplace, the employer should accomplish a comprehensive operational safety/health hazard analysis and then devise and implement an effective safeguarding system which is fully responsive to the situation. In general, the scale of the automation cell will drive the scale of the safeguarding. (Various effective safeguarding techniques are described in ANSI B11.19-2010.)

ROCKFORD SYSTEMS CAN HELP
During Rockford Systems Onsite Risk Assessments and Onsite Machine Surveys, we find one of the most common problems with robotics is the failure to accurately calculate safety distances, typically used in regard to the installation of safety mats. Robots make rapid and wide-reaching moves. The goal is to stop a robot before it can hurt someone.

Robotics Palletizer and Stretch Wrapper Cell Courtesy: Banner Engineering
Robotics Palletizer and Stretch Wrapper Cell
Courtesy: Banner Engineering

Any robot that moves more that 10 inches per second must be safeguarded adequately. Safe distance is determined by the following Robotics Industry Associations (RIA) formula with the following parameters:

DS= 63 inches per second (IPS) X(TS+ TC+ TR) + DPF
DPF= 1.2 m (48 in.)

Where:
DS= minimum safe distance
TS= stopping time of device
TC= worst stopping time of control system
TR= response time of safeguarding device including interface
DPF= maximum travel distance toward a hazard once someone has entered the field

 

So the total horizontal space to be protected is 48 in. plus 63 IPS, multiplied by the total time delay between detection of a person in the protected area and the actual time it takes for the robot to stop.

It’s imperative that the automation cell and all aspects of machine use be identified and considered when selecting and implementing a robotics safeguarding. Ultimately, the best type of protective measure will be the device or system that provides maximum protection, with minimal impact on normal machine operation.

Please call 1-800-922-7533 or visit www.rockfordsystems.com for more information.