Closing Force Measuring Device / Closing Force Transducer

Power-operated gates are machines in the sense of the European Machinery Directive 2006/42/EC. Therefore, existing gate systems are not grandfathered. Gates must therefore comply with current safety requirements today, even if they were installed correctly years ago. The selection or adaptation of safety devices must be based on an assessment of the existing risks. For this risk assessment, the accessibility, the type of control and the group of people operating the gate play a major role.

Table with assignment of the specifications for the safety measures

Devices for force limitation can be integrated into the drive unit of the power-operated door. Whether the specified limit values are observed during the use can be checked with a measuring device for closing force. If it is not possible to reduce excessive forces far enough, the dangers can be reduced by evaluations for obstacle detection. If these detect an obstacle by increasing power consumption or slowing down the closing process, the force application is stopped or the direction of movement is reversed.

The term floor detection stands for components that detect persons or objects located on the floor below the door. If a foreign object is detected, the door must stop or reverse.

Presence detection by means of a light grid or leading light barrier prevents persons or objects in the door's movement area from being touched. If the elements for presence detection are monitored by the door control system or are self-monitoring, the force measurements are not necessary.

For gates belonging to workplaces, the technical rules for workplaces must generally be applied. If power-operated gates, barriers and similar movable elements do not have a gate operator's control or monitored sensors for presence detection, the forces during closing and, if necessary, also during opening must be limited. The forces that occur must be measured and documented with a closing force measuring device when the system is installed and during the safety tests that are carried out at least once a year. The limit values to be complied with and the type and frequency of the checks are specified in the technical rules for workplaces.

Technical rules for workplaces – Doors and gates – ASR A1.7

• Item 7 Securing of leaf movement
  (3) "Vertically moving gate leaves shall be balanced by counterweights or other technical devices (e.g. drives, springs) so that they do not close unintentionally. When using gates, the force at the main closing edge may not exceed 150 N when moving through unbalanced weights."


• Item 10.1 Maintenance
  (3) "The force required for opening or closing by hand should not exceed 220 N for doors and 260 N for gates. For power-operated gates, the maximum force may be exceeded by 50 percent in justified cases."


• Item 10.2 Safety testing
  (1) "Power-operated doors and gates must be properly tested for safe condition in accordance with the manufacturer's specifications prior to initial operation, after major modifications, and periodically. The recurring test should be performed at least once a year. The results of the safety inspection should be recorded and kept in the workplace."
  
  (2) "The safety-related testing of power-operated doors and gates may only be carried out by experts who can assess the functional efficiency of the protective devices and check them using suitable measuring technology, which, for example, proves the force progression over time at closing edges."
  
  In order to be able to record and document the force progression over time at the closing edges, the closing force measuring device used must be able to measure and store the forces at short time intervals. A closing force measuring device with a drag pointer is not suitable for this purpose, as it only stores the maximum value.

Unfortunately, there have been repeated serious accidents at automatic doors, gates and other moving construction elements in the past. Therefore, safety devices have become mandatory. One possibility is to reduce the forces that occur during opening or closing to such an extent that no one gets any serious damage. Application-specific standards have defined the limits for specified opening widths that must not be exceeded. Testing of the opening and closing forces is mandatory during installation and also during periodic inspections. With a special measuring device for closing force, the acting forces can be reliably determined in accordance with the standards.

Many buildings are now equipped with automatic doors to facilitate the access to and exit from the building. Automatic doors are often installed in large department stores and shopping centres, for example, and also in administrative buildings, hotels, supermarkets, discount stores, laboratories, hospitals, nursing homes and airports. No one should be injured by these doors. Therefore, the automatic doors must be tested for safety. One of the possible safety measures is to limit the forces acting during closing and opening.

In Germany, DIN 18650 – Automatic Door Systems with its Part 1 Product Requirements and Test Methods is authoritative for closing force measurement on department store doors and other power-operated doors.

Item 5.7.3.1 of DIN 18650-1 states "Forces (crushing and impact) that occur when the door leaf hits the human body or parts of the body are limited if they do not exceed the permissible dynamic and static forces determined with a measuring device according to 6.2.2."

The permissible dynamic forces are specified as
- 400 Newton for opening widths up to 200 mm,
- 700 newtons for opening widths between 200 and 500 mm, and
- 1,400 newtons for opening widths greater than 500 mm.

The remaining static force must not exceed 150 Newtons and must decrease to 80 Newtons within 5 seconds.

Diagram of the force curve on the door leaf according to DIN 18650-1

The measuring points are clearly shown and dimensioned in figures for the different door types in Appendix B of DIN 18650-1.

The following requirements are placed on the closing force measuring device in item 6.22 of this standard:

• The measuring device for closing force must have contact surfaces with a diameter of approx. 80 mm for force absorption.
  These must be made of hard and solid material, e.g. steel.
• The spring arranged between them should have a spring stiffness of 500 N/mm ± 50 N/mm.
• The device must be capable of detecting the force for the measuring range from 25 to 2 000 Newton.
• The time of force application must be measured from 0 to 5 seconds, with a time constant less than 5 milliseconds for force increase and drop.
• The measurement error must not exceed 5% for the entire range of values.
• The measured values must be displayed or transmitted.

The standard thus specifies that a closing force measuring device must be used with which a force-time curve can be measured, recorded and displayed for at least five seconds. A digital measuring device for closing force with a very short measuring and storage cycle is suitable for this purpose.

Closing force measurement on elevator doors
Passenger and freight elevators enable large differences in height to be overcome in a short time and without physical exertion. Elevators, especially those for passenger transportation, are often also referred to as lifts. According to Paragraph 2 No. 30 of the Product Safety Act, the elevators are systems requiring monitoring. The safety requirements apply both to the planning and construction of the elevator systems and to their operation..

The technical rule for operational safety – TRBS 3121 – Operation of elevator systems
recommends the following technical protective devices as protective measures against shock, pull-in and crushing hazards on elevator doors:

- Changing the direction of movement if an obstacle is detected when closing the doors, and
- Limiting the closing force to 150 Newtons and the kinetic energy to 10 joules.

These protective measures have already been implemented in the majority of elevators open to public. If a person or object is in the closing area, the doors do not close. They either move back before impact or exert only low forces on impact so that no injuries occur.

Elevator manufacturers and operators are responsible for ensuring compliance with the safety regulations. As a rule, the required tests are performed by approved experts. These experts perform

- the prescribed tests before the first operation
- the commissioning of the elevator and
- the necessary periodic inspections.

Depending on the design of the door systems for the car and elevator shaft, the inspections also include measuring the force or kinetic energy when closing the doors with a suitable measuring device for closing force. The closing force measuring device used should be simple and safe to use, enable precise measurements and also be able to store or transmit the measurement data.

Directive 2000/4/EC amended the EU approval regulations for class M motor vehicles in Directive 74/60/EEC with regard to vehicle interior equipment. This is intended to reduce the risk of injury associated with power windows and power sunroofs. Since 2003, in vehicles registered for the first time, where closing operations are triggered by merely tapping a switch, the moving elements must automatically reverse the direction of movement if their closing edge encounters an obstacle. After hitting an obstacle several times, however, this anti-trap protection is usually deactivated, since most systems cannot distinguish what is preventing the closing.

This regulation does not necessarily apply to automatic locking systems that only work when the ignition is switched on or where the switch must be permanently actuated. However, many vehicle manufacturers also take anti-trap protection into account in these designs. When evaluating ADAC new car tests, however, it is noticeable that about one in five of the vehicles tested by ADAC has no or incomplete anti-trap protection.

Automatic reversing devices must be effective in the opening range of 4 to 200 mm before a force of 100 Newtons is reached. The forces that occur can be tested with a specially designed measuring device for closing force. To do this, the external sensor from the closing force measuring device is usually placed at right angles on one of the closing edges of the automatic window, sliding door or sliding roof and then loaded by the closing process. The force-related deformation of the sensor must not exceed 10 N/mm for the measurements according to the EC standard.

The models of the measuring device for closing force differ, for example:

Those who want to purchase a closing force measuring device for measurements on motor vehicles, should also pay attention to the functions and handling of the display and operating unit. In the case of the vehicles produced for other countries, the regulations applicable there for the clamping protection must also be observed,

• in the USA FMVSS 118,
• in Canada CMVSS 118,
• in Brazil Contran 762/1992,
• in Korea Regulation 1002,
• • in Australia ADR 42/03.

The main inspection and safety inspection of buses in accordance with § 29 StVZO Annex VIII (HU, SP) also includes a check of the closing forces on the passenger doors. The conditions for the measurement and the minimum requirements for the closing force measuring device to be used are defined in Annex V of the Directive 2001/85/EC "Guidelines for measuring the closing forces of power-operated doors". The mechanical closing force measuring device described in this annex of the standard only allows the measurement of the respective peak forces. The peak force may exceed 150 Newtons for a short time during the measurements, but not 300 Newtons.

Point 7.6.5 of the Directive 2001/85/EC lists "Additional technical requirements for power-operated service doors". It states that the closing bus door must automatically reopen when it encounters an effective force of up to 150 Newtons. It further states that the effective force can be measured with any suitable closing force measuring device that uses a method approved by the authority having jurisdiction. The electronic closing force gauge can be used to measure and display both peak and effective forces. Sturdy test rods can be used to check whether the doors reopen as intended and whether any objects or body parts trapped by the doors can be easily pulled out again. The dimensions of these test rods are specified in the guideline.

Separate regulations apply to rail-bound vehicles for passenger transport:

- Ordinance on the Construction and Operation of Tramways (Tramway Construction and Operation Ordinance – BOStrab).
- Railroad Construction and Operation Regulations (EBO)
- EN 14752 Railway applications – Side entry systems for rail vehicles
- VDV 111 Requirements for the protection against trapping and injury on doors and power-operated steps of mass transit rail vehicles
- VDV Specification 157 Requirements for the protection against entrapment and injury as well as emergency opening devices on doors of passenger vehicles according to BOStrab

The EN 14752 describes the specifications for the design and operation of passenger doors on rail vehicles. The regulation is intended to ensure the permanent function of these doors and to minimize the risk of injury. The publications 111 and 157 issued by the Association of German Transport Companies (VDV) also provide recommendations for increasing safety on the automatically operated doors of tram, light rail and subway vehicles.

The VDV 111 lists not only the power-operated doors, but also steps that are moved automatically for getting in and out. The door and step are considered as one door system. The anti-trap protection must be tested not only on the door but also on the step with the measuring device for closing force. Depending on the applicable regulation, measurements are taken once, twice or three times per measuring point. The electronic closing force measuring device with data memory considerably simplifies the measurement procedure and evaluation.

Many workpieces and molds must be held securely during the production process. The forces applied to the parts by the holding device can be checked with the closing force measuring device. The force measurement is particularly recommended for machine holding devices for sensitive parts. With the help of the values determined by the closing force measuring device, the holding force of the machine or fixture can be precisely adapted to the respective task.

On injection molding machines, the forces for pressing the mold halves together must be precisely matched to the material, size and shape of the injection molded part. The force must be set neither too low nor too high. Excessive closing forces endanger the mold and affect compression and cooling of the casting. Before a new product series is injected, the force can be determined with the closing force gauge and corrected up or down if necessary. The force-locking gripping devices of robots, vehicles or transport systems must also be set correctly.

Otherwise, there is a risk that picked-up parts or containers will slip off or that they will be damaged by excessive pressure. The measuring device for closing force must have a suitable force sensor to determine the currently acting force. Both the dimensions of the sensor and its measuring range must be suitable for the gripping device to be tested. For grippers with several clamping points, it is recommended to use the closing force measuring device with several sensors so that all clamping forces can be recorded simultaneously in one measurement.