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Course 726 - Introduction to Machine Guarding

Safety guides and audits to make your job as a safety professional easier

Methods of Machine Safeguarding (Continued)

Dangerous parts can be located high enough to be out of the normal reach of any worker.
Dangerous parts guarded by location.

Safeguarding by Location and Distance

To consider a part of a machine to be safeguarded by location, the dangerous moving part of a machine must be so positioned that those areas are not accessible or do not present a hazard to a worker during the normal operation of the machine. This may be accomplished by locating a machine so that the hazardous parts of the machine are located away from operator work stations or other areas where employees walk or work. This can be accomplished by positioning a machine with its power transmission apparatus against a wall and leaving all routine operations conducted on the other side of the machine. Additionally, enclosure walls or fences can restrict access to machines. Another possible solution is to have dangerous parts located high enough to be out of the normal reach of any worker.

The feeding process can be safeguarded by location if a safe distance can be maintained to protect the worker's hands. The dimensions of the stock being worked on may provide adequate safety.

For instance, if the stock is several feet long and only one end of the stock is being worked on, the operator may be able to hold the opposite end while the work is being performed. An example would be a single-end punching machine. However, depending upon the machine, protection might still be required for other personnel.

The positioning of the operator's control station provides another potential approach to safeguarding by location. Operator controls may be located at a safe distance from the machine if there is no reason for the operator to tend it.

1. To consider a machine safeguarded by location, the hazardous parts of the machine must be so positioned so that they _____.

a. are not visible
b. are not within arm's length
c. do not present a hazard during normal operation
d. will not move if the guard is removed

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Feeding and Ejection Methods

gsg photo - Auto Feed System
Automatic Feed System. Power Press with Automatic Feed

Many feeding and ejection methods do not require the operator to place his or her hands in the danger area. In some cases, no operator involvement is necessary after the machine is set up. In other situations, operators can manually feed the stock with the assistance of a feeding mechanism. Properly designed ejection methods do not require any operator involvement after the machine starts to function.

Some feeding and ejection methods may even create hazards themselves. For instance, a robot may eliminate the need for an operator to be near the machine but may create a new hazard itself by the movement of its arm.

Using these feeding and ejection methods does not eliminate the need for guards and devices. Guards and devices must be used wherever they are necessary and possible in order to provide protection from exposure to hazards.

Automatic Feed Systems

Automatic feeds such as the figure to the right reduce the exposure of the operator during the work process, and sometimes do not require any effort by the operator after the machine is set up and running.

2. Properly designed _____ do not require any operator involvement after the machine starts to function.

a. ejection methods
b. injection methods
c. semi-automatic feeding methods
d. robotic feeding systems

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Semi-Automatic Feeding Systems

With semi-automatic feeding in figure 1, as in the case of a power press, the operator uses a mechanism to place the piece being processed under the ram at each stroke. The operator does not need to reach into the danger area, and the danger area is completely enclosed.

Semi-Automatic Ejection Systems

Figure 2 shows a semi-automatic ejection mechanism used on a power press. When the plunger is withdrawn from the die area, the ejector leg, which is mechanically coupled to the plunger, kicks the completed work out.

gsg Semi auto feed
Semi-Automatic Ejection. Stock is ejected by an ejector leg.
gsg photo - Manual feed
Semi-Automatic Feeding System. Manually feed without reaching into the point of operation or another danger zone.

3. With _____ feeding when operating a power press, the operator uses a mechanism to place the piece being processed under the ram at each stroke.

a. continual
b. robotic
c. automatic
d. semi-automatic

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Robot Systems

Robots are used for replacing humans who were performing unsafe, hazardous, highly repetitive, and unpleasant tasks
Robots are used for replacing humans who were performing unsafe, hazardous, highly repetitive, and unpleasant tasks.

Essentially, robots perform work that would otherwise have to be done by an operator. They are best used in high-production processes requiring repeated routines where they prevent other hazards to employees. However, they may create hazards themselves, and if they do, appropriate guards must be used.

Robots are machines that load and unload stock, assemble parts, transfer objects, or perform other tasks.

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.

All industrial robots are either servo or non-servo controlled.

Servo robots are controlled through the use of sensors which are employed to continually monitor the robot's axes for positional and velocity feedback information. This feedback information is compared on an on-going basis to pre-taught information which has been programmed and stored in the robot's memory.

Non-servo robots do not have the feedback capability of monitoring the robot's axes and velocity and comparing with a pre-taught program. Their axes are controlled through a system of mechanical stops and limit switches to control the robot's movement.

4. Which type of robot system uses a pre-taught learning program to monitor its movement and velocity?

a. Non-Servo
b. Servo
c. Automatic
d. Programmed

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Robot Systems (Continued)

Types of Robot Hazards

The use of robotics in the workplace also can pose potential mechanical and human hazards.

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 unpredicted movements, component malfunctions, or unpredicted program changes.

A 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 to name a few.

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 unpredicted movement or action by the robot which can result in personnel injury or equipment breakage.

Human errors in judgment result frequently 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.

The three figures on this page show a type of robot in operation, the danger areas it can create, and an example of the kind of task (feeding a press) it can perform.

gsg photo robot guard
Guarding Robot Systems. Fixed guard placed around robot.
gsg photo - robot movement
Robot Systems. Robot movement capability.
gsg photo - Robot Danger Zones
Robot Systems. Potential Danger Areas

5. What is the greatest human judgment error when working around robots?

a. Employees connecting input/output sensors
b. Employees are too trusting of redundant robot motions
c. Employees assume robots are not activated upon entering danger zones
d. Employees being crushed by peripheral equipment

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Miscellaneous Aids

While these aids do not give complete protection from machine hazards, they may provide the operator with an extra margin of safety. Sound judgment is needed in their application and usage. Below are a couple of examples of possible applications.

An awareness barrier does not provide physical protection, but serves only to remind a person that he or she is approaching the danger area. Generally, awareness barriers are not considered adequate when continual exposure to the hazard exists.

The figure on the left, below, shows a rope used as an awareness barrier on the rear of a power squaring shear. Although the barrier does not physically prevent a person from entering the danger area, it calls attention to it. For an employee to enter the danger area an overt act must take place, that is, the employee must either reach or step over, under or through the barrier.

Shields, another aid, may be used to provide protection from flying particles, splashing cutting oils, or coolants. Figure 2 shows more potential applications.

gag photo
Shields. Transparent Shields on Drill and Lathe
gsg photo
Awareness Barriers. Rear View of Power Squaring Shear

6. Which of the following is not considered adequate protection when continual exposure to a hazard exists?

a. Hand tools
b. Awareness barrier
c. Shields
d. Push sticks

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Miscellaneous Aids (Continued)

Special hand tools may be used to place or remove stock, particularly from or into the point of operation of a machine. A typical use would be for reaching into the danger area of a press or press brake. Figure 1 below shows an assortment of tools for this purpose. Holding tools should not be used instead of other machine safeguards; they are merely a supplement to the protection that other guards provide.

A push stick or block, such as those in the figure below may be used when feeding stock into a saw blade. When it becomes necessary for hands to be in close proximity to the blade, the push stick or block may provide a few inches of safety and prevent a severe injury. In figure 2, the push block fits over the fence.

gsg photo - Interlocked
Special Hand Tools. Push stick and block.
gsg photo Rubber Mill
Special Hand Tools. Special hand tools.

7. Which of the following is a miscellaneous aid that should be used when feeding stock into a saw blade?

a. A push stick or block
b. A holding tool
c. Vacu-tongs
d. A pair of feeding tongs

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