The STM (stop-time measurement) device measures the time it takes a machine to stop after a signal is given. It is mainly used on reciprocating (stroking or cycling) machines, such as mechanical or hydraulic presses and press brakes. With optional accessories, it can also be used on machines that rotate, such as lathes, mills, and drills.
- Easy to use in the field
- Portable; battery-operated
- Readout in stopping time or safety distance
- Handy carrying case
- Optional remote tachometer assembly
- Optional manual start switch set
Industry uses this type of device to find the stopping time of a machine before installing safeguarding devices such as a two-hand control or a presence-sensing device. The stopping time measured by the STM device during the hazardous portion of the cycle is used in the OSHA (Occupational Safety and Health Administration) or ANSI (American National Standards Institute) formulas to calculate the safety distance. The safety distance is then used to establish the location of the safeguarding device in relation to the nearest hazard. This device can also be used to periodically check the machine’s stopping time to ensure that the current safety distance corresponds to the current condition of the machine’s stopping ability.
This STM device is also used by federal and state OSHA compliance officers, insurance company loss-control engineers, and safety training personnel to determine if proper safety distances are being used for the existing safeguarding method.
The portable design makes the STM very easy to use. A programmed stop signal is provided, which releases or actuates a button or other operator-controlled device on the machine during the hazardous portion of the cycle. If a machine has a presence-sensing device, the plane of light can be interrupted with the furnished flag, which sends a signal to stop the machine.
When using this STM device, the display gives either the stopping time of the machine in milliseconds (thousandths of a second), or the calculated safety distance in inches. The safety distance is based on the hand speed constant of 63 inches (1.6 meters) per second. For mechanical power presses, the OSHA formula multiplies the hand speed constant by the stopping time of the machine at 90° of crankshaft rotation. When using this formula, the reaction time of either ergonomic (capacitive) palm buttons or a presence-sensing device should be added to the stopping time to calculate the proper safety distance.
This device consists of three major components:
- The meter which is the processor containing the electronics and display.
- The position/velocity transducer which detects motion and provides the programmed output signal to stop the machine.
- The hand-held actuator which automatically releases or pushes a button or other device on the machine. It is also used to operate the flag when presence-sensing devices are used as the safeguarding method.
Other STM components and literature provided with this device are the presence-sensing flag, cable extension set, legs, plunger extension, and instruction manual. Optional equipment consists of a remote tachometer assembly (for machines that stop beyond bottom or top dead center and for rotating machines) and a manual start switch.