Safety Foot Switch: Working Principle, Applications, Types

What is a safety foot switch?

The safety foot switch is a foot-operated emergency stop device used on machines when operation by hand is not possible if a hazardous status arises. Most of the safety foot switches are equipped with an ergonomic protective shield against unintentional actuation.

Working principle

The safety foot switch has two contact blocks, each with one NO contact and one NC contact. Two contact blocks are connected for easy connection of a single-phase motor. (1) The normal workflow is initiated by pressing down the pedal as far as the pressure point so that the two NO contacts close and the motor starts to run. (2)

If in the event of danger the pedal is pressed beyond the resistance of the pressure point, the positively driven NC contacts will open and the motor is stopped. (3) At the same time, the independent latching takes effect and holds the NC contacts in the open position. This prevents the machine parts from continuing to run out of control or from being restarted.

After the hazard is eliminated, the machine can only be restarted after manually releasing the switch using a pushbutton on the top of the enclosure. (4) The contacts are then released again and return to their initial position (the NO contacts are open and the NC contacts are closed). (5)

Applications

The foot-operated safety switch has been developed for industrial application with high mechanical and electrical endurance. The safety foot switch can be used in machines such as:

• Adhesive dispensers
• Abrasive blasters
• Packaging equipment
• Conveyers
• Material handling equipment
• Man lifts
• Communications equipment
• Lighting
• Engine brake
• Alarms / Security
• Emergency vehicles – Siren / Horn
• Terminal applicators
• Degreasers
• Metalworking machines
• Electric vehicles
• Farm equipment
• Engravers machinery
• Scissor lifts
• Riveting machinery
• Soldering / Desoldering / UV Curing / Welding Equipment

Types

Safety foot switches come in three operation formats.

1-Free movement

Contact position follows pedal movement: actuated when the pedal is pushed down, released when the pedal is in a state of rest.

2-Foot switch locked in the neutral position

The same operation as above, after unlocking the pedal with the end of the foot.

3-Foot switch latched in the low position

The same operation as free movement, except that a state of rest is obtained only after having unlatched the pedal with the end of the foot.

Construction

Selection parameters

The type or model of safety foot switch suitable for each application will vary depending on factors such as the control function required, degree of protection required, production methods, unusual conditions, government regulations, etc. In some applications, more than one safety foot switch may be required, as when two or more persons are operating a machine. In these cases, safe practices and regulations require that the safety foot switches be wired in series making it necessary that each operator’s safety foot switch be actuated before the machine will cycle.

Only the user can be aware of all the conditions and factors present during the setup, operation, and maintenance of the machine; therefore, only the user can determine which safety foot switch(es) can be properly used. When selecting a safety foot switch for a particular application, the user should refer to the applicable ANSI standards and OSHA regulations. The National Safety Council’s Accident Prevention Manual also provides much useful information.

In some applications, such as power presses, additional operator protection such as point-of-operation guarding must be provided when a safety foot switch is used as an actuator. This is necessary since the operator’s hands and other parts of the body are free to enter the pinch point area and serious injury can occur. The shielding provided on them cannot protect an operator from injury. For this reason, the safety foot switch cannot be substituted for or take the place of point-of-operation protection.

Maintenance

Every week: Check the correct operation of pedals. Remove all dirt or particles on the switch that may affect function. Check enclosure and cable for damages and impurities.

Every 6 months: Lubricate cam and roller shafts. Isolate power and remove the cover. Check screw terminal tightness and check for signs of moisture ingress.