Measuring and testing – Dynamometers – Responsive to force
Patent
1982-08-18
1984-12-04
Ruehl, Charles A.
Measuring and testing
Dynamometers
Responsive to force
7386265, G01D 112, G01L 122
Patent
active
044856830
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a portable measuring instrument for measuring the clamping force between a pair of welding electrodes in spot welding.
The working control cycle of a mechanically driven spot welding machine is initiated by an impulse from a welding timer activating the valve which controls the working cylinder providing the electrode movement and force. When a predetermined electrode force has been reached, the welding process itself is initiated by the welding current being turned on in the conventional automatic manner. The time from the moment the valve controlling the electrode movement is activated up to the moment when the current is turned on is called the squeeze time, and it is of great importance that this time be correctly set. If it is too short, insufficient electrode force will be built up, resulting in poor weld quality. If it is too long, the welding cycle will be unnecessarily extended, lowering the rate of production.
The length of the required squeeze time is dependent on a number of factors, such as the type of welding machine, air or hydraulic operation, valve and pipe arrangements, requirements for quiet and smooth operation of the equipment, etc. Thus it is not possible to give any general values of the length of the squeeze time.
Methods known up to now for checking that the squeeze time has a suitable length are relatively complicated and involve the moving of a recording oscilloscope with the necessary adaptor equipment to the welding machine as well as hooking up and adjustment. Disruption of production is thus unavoidable.
The purpose of the present invention is to achieve a measuring instrument which provides directly information on the squeeze process and which is small enough to be easily carried on one's person. A further purpose is to achieve an instrument which does not require special electrical connection to the welding machine thus disrupting production only very minimally.
This is achieved according to the invention by means of an instrument which has a load cell equipped with a wire strain bridge for example, which can be inserted between a pair of welding electrodes to measure the clamping force therebetween and which is coordinated with a pair of electrodes in a voltage detector to indicate voltage between the welding electrodes, the load cell and the voltage detector being coupled to an electronic unit with optical indicating means, which indicate the size of the clamping force at the moment when voltage appears between the welding electrodes.
The instrument according to the invention provides information on the magnitude of the clamping force when the welding current is turned on, which makes it possible to determine directly whether the squeeze time is too short or too long.
The invention will be described in more detail with reference to the embodiment shown on the accompanying drawings, of which:
FIGS. 1 and 2 show a side view and a plan view respectively of one embodiment of an instrument according to the invention,
FIG. 3 shows a block diagram of the instrument electronics, and,
FIG. 4 shows a diagram of the clamping force as a function of time during one welding cycle.
The instrument according to the invention comprises a measuring cell, generally designated 1 which, via a flexible connection 2 of rubber for example, is connected to an apparatus casing 3 containing the electronics shown in the block diagram in FIG. 3.
The measuring cell 1, which is intended to be inserted between a pair of welding electrodes 4 in a spot welding machine, has a pair of circular plates 5 of electrically conducting material which are electrically insulated from each other by means of an intermediate insulation. The plates 5 are provided with flat striking surfaces 6 and carry between them a force measuring means in the form of a wire strain bridge 7 (see FIG. 3).
On the apparatus casing 3, which also serves as a handle for use of the instrument, there is an optical indicator in the form of a scale 8 with a stack of light-emitting diodes 9 indicating the clamping
REFERENCES:
patent: 2430237 (1947-11-01), Moncher
patent: 2616014 (1952-10-01), Ellerby
patent: 2744182 (1956-05-01), Gross
patent: 3222923 (1965-12-01), Lebow
patent: 4307608 (1981-12-01), Useldinger et al.
AB Volvo
Giebel James R.
Ruehl Charles A.
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