Two-Hand Control Safety Distance (Minimum Distance)

Install all hand controls far enough away from the nearest hazard point that the operator cannot reach the hazard with a hand or

other body part before the hazardous motion ceases. This is the separation distance (safety distance), and may be calculated as

follows.

WARNING:

•

Mount hand controls at a safe distance from moving machine parts

•

Failure to establish and maintain the safety distance (minimum distance) could result in serious injury or

death.

•

Mount hand controls as determined by the applicable standard. The operator or other non-qualified

persons must not be able to relocate the hand controls.

U.S. Applications

The Safety Distance formula, as provided in ANSI B11.19:

Part-Revolution Clutch Machinery (the machine and its controls allow the machine to stop motion during the hazardous portion of

the machine cycle)

Ds = K x (Ts + Tr) + Dpf

For Full-Revolution Clutch Machinery (the machine and its controls are designed to complete a full machine cycle)

Ds = K x (Tm + Tr + Th)

Ds

the Safety Distance (in inches)

K

the OSHA/ANSI recommended hand-speed constant (in inches per second), in most cases is calculated at 63 in/s, but may

vary between 63 in/s to 100 in/s based on the application circumstances;

not a conclusive determination; consider all factors, including the physical ability of the operator, when determining the

value of K to be used.

Th

the response time of the slowest hand control from the time when a hand disengages that control until the switch opens;

Th is usually insignificant for purely mechanical switches. However, Th should be considered for safety distance calculation

when using electronic or electromechanical (powered) hand controls.

For Banner Engineering Self-checking Touch Buttons (STBs) the response time is 0.02 seconds.

Tm

the maximum time (in seconds) the machine takes to cease all motion after it has been tripped. For full revolution clutch

presses with only one engaging point, Tm is equal to the time necessary for one and one-half revolutions of the crankshaft.

For full revolution clutch presses with more than one engaging point, Tm is calculated as follows:

Tm = (1/2 + 1/N) x Tcy

N = number of clutch engaging points per revolution

Tcy = time (in seconds) necessary to complete one revolution of the crankshaft

Tr

the response time of the Safety Controller as measured from the time a stop signal from either hand control is received.

The Safety Controller response time is obtained from the Configuration Summary tab in the Software.

Ts

the overall stop time of the machine (in seconds) from the initial stop signal to the final ceasing of all motion, including stop

times of all relevant control elements and measured at maximum machine velocity.

Ts is usually measured by a stop-time measuring device. If the specified machine stop time is used, add at least 20% as a

safety factor to account for brake system deterioration. If the stop-time of the two redundant machine control elements is

unequal, the slower of the two times must be used for calculating the separation distance.

European Applications

The Minimum Distance Formula, as provided in EN 13855:

S = (K x T) + C

S

the Minimum Distance (in millimeters)

STB Self-Checking Optical Touch Buttons

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