The present application refers to a method of measuring stop time and stop distance of a movable part of a machine or the like, by means of an apparatus incorporating a computer for processing and visualizing and/or printing out measuring and time data .

The invention also incorporates a device for accomplishing the method .

Background of the invention

According to the Swedish National Working Environment Act a machine supplier is responsible for a machine at delivery being "secure" , i.a. by having protective devices according to prevailing regulations. For some machines, e.g. presses and power shears, it is called for declaration of stop time and safety distance. The safety distance is intended for securing that the machine operator shall have no time to get a hand or the lil<e into the tool at a so called-- post-grip, i.e. a reflective action during a machine movement. The manual work at presses is most often monotonous and fatiguing. The operator makes up to 15.000 actions in the tool during a working day. The work cycles are of short duration and the sitting position is bad, firstly due to the press design and secondly due to the fact that the operator frequently must reach far to the tool from the two-hand-guard or a light curtain. The safety distance is determined by the stop time of the press. The stop time thereby is considered as the reaction time measured from the moment when e.g. a knob in a two-hand-guard is released until the machine has slowed down. The operator gives a starting signal with such detection guards, which can be two-hand-guards or light curtain guards (optical detection of the position of parts of the body) . The signal is fed to the machine control system, which controls if there is any hinder for start. If that is not so, start is ordered by means of a signal to the driving system. The

driving system transfers its power to the movable machine member, e.g. a slider for a press tool, which starts its work cycle, whereby the tool halves form the work piece. The movement of the slider will be stopped if the two-hand-guard is released or if the light curtain is affected.

As the risk for post-grip at some machines, particularly presses and shears, is evident, these machines require a safe stop function with a certain maximum stop time. The requirement is that there shall be a certain safety distance to the risk zone of the machine to prevent the operator from reaching the risk zone before the tool has stopped or has reached an unharmful position. The National Swedish Board of Occupational Safety and Health has determined the hand speed ^" to 1.6 m/sec for two-hand-proteced work and 2.5 m/sec at picking work in connection to light curtain. Long stop times however also give long safety distances resulting in a bad power ergonomy, if the work is carried out at the correct

_^ safety distance. The risk that the safety distance under such conditions will not be considered increases, which gives a bigger risk for accidents.

The purpose and most essential features of the invention

> Trie purpose of the present invention is to provide a method enabling very accurate measurement of the stop time and stop distance of the machine without the necessity of tampering with the machine. Another purpose is to provide an analysis instrument by means of which maintenance crew, safety personnel, designers and others can study the stop and movement process of existing and new machines. Such an analysis equipment must be so simple that also practicians lacking computer knowledge shall be able to use the instrument, i.a. in order to obtain such a low limit value as possible for the safety distance and thereby to improve the ergonomy at press work. A further object of the invention is to make possible study of how the stop process is composed, in order to separate the influence upon the stop time from mechanical, electrical and other components, and thereby

making possible the use of the instrument as a diagnostic equipment. It shall furthermore be possible to produce it at a price substantially lower than that of conventional electronical slip and speed measuring systems. These tasks have been solved by fitting to the movable machine member a distance transducer, which transfers information about position, direction and speed of the movable machine member to the computer, feeding the desired stop position for the movable machine member to the computer, applying at or against the detection guard an actuator, which is connected to the computer and intended for mechanically trigging the stop process of the machine, and when the stop position has been reached trigging the actuator, and synchronizing the stop signal for the machine with the start of the data collection in the computer, whereby the input data on the stop process from the distance tranducer is stored and/or visualized therein .

The invention also incorporates a device for performing the method, the characteristics of which are further presented in claim 3.

Description of the drawings

The invention hereinafter will be further described as an embodiment with reference to the accompanying drawings. Figure 1 shows a block diagram over the main components forming part of the apparatus according to the invention. Figure 2 shows the apparatus according to the invention used in connection with a schematically shown press.

Figure 3 shows a section through the actuator forming part of the device according to the invention.

Description of embodiments

The apparatus according to the invention incorporates a conventional computer 11 , preferably a microprocessor, having a keybord 12, a display 13, an internal memory 14, a cassette tape unit 15 and a printer 16. This standard computer has been

equipped with a counter card 17 having two input terminals for a distance transducer 18 and one output terminal 19, a double PIA card 20 having input and output gates for connection of external components 21 and input and output gates for connection of an actuator 22. The PIA card can also be equipped with two further output terminals for connection of the relay boxes 23 of the machine.

In figure 2 is shown the apparatus according to figure 1 used at a press 24, which consists of a slider 25, which carries a movable press tool 26, which cooperates with a fixed tool 27. The slider 25 gets its movement and power from a driving and retarding system 28, which is operated via a control system 29 by. a, detection guard 30, which e.g. can be a two-hand-guard incorporating two operating members 31 (one of which is shown only) or a light curtain guard.

The distance transducer 18 in the example shown is constituted by an angular transducer of incremental type, e.g. a digital position/displacement transducer, where the transducer is driven by a cable 32 supported upon a spring biased cassette inside the transducer housing. At the- free end of the cable 32 there is fitted an attachment member, e.g. a magnetic disc 33, which is fitted to the movable press tool 26, whereas the housing of the transducer 18 temporarily is fixedly attached tα the press 2 .

The actuator 22 consists of an oblong housing 33 , in which is supported an axially displaceable operating member 34 shaped as a bar, a tube or the like, the two end portions 35 and 36 of which are situated outside the housing. Upon the operating means inside the housing there is fixedly arranged a sleeve shaped stop 37 for a pressure spring 38 arranged upon the operating means 34, which spring at its opposite end rests against one end side 39 of the housing. Alongside the operating means and in parallel therewith a slide 40 is isplaceably arranged in a guide 41 , which slide in front of the sleeve shaped stop 37 is provided with a stud 42 arranged to block and release an arm 43, which is pivotably supported

on a shaft journal 44. At the free end of the arm there is arranged a roller 45. The slide 40 is axially displaceable by means of appropriate driving means , which in the embodiment shown consist of two cooperating electromagnets 46. The outer end surface 47 of the stop 37, which surface cooperates with the roller 45 is made slightly tapering, thus that the roller under influence of the pressure from the spring 38 is urged in a direction towards the stud 42. When the electromagnets 46 are activated the slide 40 and thereby the stud 42 will be displaced in a direction away from the stop 37, thus that the arm 43 with the roller 45 releases the operating means and this will with lightning rapidity be displaced towards a stop due to the spring force.

Some distance in front of the trapped stop 37 there is in the housing arranged a transducer 48, which contactfree will sense when the tapering front surface 47 of the stop 37 passes the transducer 48. This is via a circuit -49 connected to the computer 11. When trapping the operating means 34 this is displaced against the action of the spring 38, at which displacement motion is engaged a carrier 50, which with a hook ^' 5-1 carries along the s ^' tud 42, thus -- that this will be situated in front of the roller 45.

One or the other end 35, 36 of the operating means of the actuator can be used due to the type of detection guard. If the detection guard is a two-hand-guard, i.e. two operating members which simultaneously must be pressed down for allowing the machine to start, whereas it stops by the operating members being released, one end portion 36 of the operating means 34 is located on one of the operating members 31 (Figure 2) , as a mechanic hand, whereas the other hand is placed upon the other operating member. The machine is started by the two operating members being pressed down, whereby the control system 29 of the press 24 obtains an impulse to start the driving system 28 of the press 24, which thereby lowers the slider 25 with the tool 26 in a direction towards the fixed tool 27. The cable 32 in the distance transducer 18 is simultaneously made shorter, which information is fed to the

computer. When the computer-stored stop position of the tool 26 is reached the computer initiates a stop signal via the circuit 52 to the driving means of the actuator, i.e. the magnets 46, which displace the slide 40 thus that the arm 43 releases the operating means 34. This is displaced at the speed of lightning by means of the pressure spring 38, whereby the transducer 48, at the moment it is passed by the tapering end wall 47 of the stop 37, transfers a signal to the computer meaning that one operating member 31 of the detection guard 30 has- been released and that the stop process of the machine has started. The distance transducer 18 continues to register the continued movement of the slider 25 and the movable tool 26 until thes_e have been stopped or for certain applications have been re-ta-rd.ecfc to a certain low speed.

The stop process of the machine can also be recorded upon a tape by aid. of the computer printer 16, whereby data about the machine stroke, maximum and minimum positions and desired stop position are obtained as fixed values. The printer furthermore . prints ou.t the measured stop time, stop distance and the possible- ex:cess motion, whereby is meant the distance the machine, mσve ^' s -from a certain stop speed, e.g. 10 mm/sec until it is completely immobile. The printer furthermore preferably plots a diagram over the stop process, whereby the time in ^" millisetrond.s is set out on the abscissa and the speed in mm/sec- and the stop distance in mm on the ordinate.

If the operating member of the detection guard is such that it must be subjected to a pressure actuation for stopping the machine, the end portion 35 of the operating means 34 is used, which end portion when the actuator is activated gives this a pushing movement. If the detection guard should be an optic device, e.g. a light curtain, then a screening device, e.g. formed by a sheet metal disc is mounted upon one end 35 or 36 resp. of the operating means 34, which device when the actuator is trigged is brought to interrupt the beam path of the light curtain.

Due to the position where the stop signal is given it is

possible to effect overall time measurements and part time measurements. If it is desired to study how the stop process is combined, i.e. which mechanical, electrical and other components 21 , that influence the stop time, said components are connected to the gates of the PIA card 20, whereby sequential measurements upon their relative switching in or switching off times can be effected. Sometimes it can also be necessary to connect one or more of the machine starting and/or stopping relays 23 or the like, which also can be done to additional gates of the PIA card 20.

The invention is not limited to the embodiment shown, but a plurality of variations are possible within the scope of the claims .