DESCRIPTION (Automatic Machine)
This automatic, computer controlled machine enables rapid, precision measurement of a broad range of compression and extension springs. The machine incorporates a wide array of standard features designed to make spring load testing both efficient and accurate. The LTE-1000 Plus comprises 5 main elements:
- Rigid loading frame.
- Measuring system incorporating state-of-the-art load and length transducers.
- Advanced stepper motor drive system.
- Industry standard, PC Compatible, controlling/data-logging computer.
- Custom written Windows based control software.
Accurate spring load testing can only be accomplished if the basic loading frame (including the load cell system) is rigid and does not deflect under the applied loading from the spring under test. Although some calculated compensation can be applied on computer-based testers, the adjustment can never be exact under all test conditions. The amount of compensation must therefore be kept to an absolute minimum by careful attention to the load frame design.
The bench mounted loading frame on the LTE is of the proven “H” type design, comprising two substantial guide pillars, which precisely align the aluminium moving crosshead. Aluminium was selected to give high strength coupled with minimum weight. These properties provide the optimum combination of maximum rigidity and high operating speed.
The loading platens are made from steel hardened to 58 Rc min. to minimise wear and maintain accuracy over many years of continuous operation. After hardening, the platens are ground, and lapped to minimise out-of-flatness and a built-in adjustment mechanism enables the platens to be exactly aligned and fixed for parallelism at the assembly stage.
In order to facilitate load testing of extension springs, a set of standard loading hooks are supplied with the machine. The loading pins on which the spring hooks are seated are easily interchanged to enable the use of specially machined pins for particular spring hook dimensions.
All these loading frame design features combine to provide absolute confidence that the load test results obtained are to the highest possible standard of accuracy.
At the heart of any spring load tester are the load and length measuring systems, and if measurement accuracy is the goal, no compromise can be accepted with the components used. In particular, budget load cells designed for dead weight measurement are not acceptable in spring tester applications.
On the LTE, spring load is measured using a high precision load cell mounted to the bottom of the loading frame. The type of load cell selected was specifically chosen for its rigidity and high level of insensitivity to non-axial spring forces. The result is a machine that minimises the effect of spring position and orientation upon the measured load.
The output signal from the load cell is fed to the computer via a single range amplifier and a 20-bit A-D converter. This combination provides stable load reading over a wide temperature range.
The loadcell system on the LTE-1000 Plus has a capacity 1000N and has a calibrated accuracy of 0.5% of reading from 0.5% to full scale giving a working range of 5-1000N. This arrangement provides the highest possible accuracy across the widest possible load range on a single machine. The display software enables the load to be displayed in units of lbf, N, kgf, or gmf.
The load cell incorporates a mechanical overload device to provide a high level of damage protection due to incorrect use.
Spring length is measured using a 5µm (~0.00025inch) digital transducer. The output signal from the transducer is fed to associated processing and interface electronics to produce a displayed resolution of 10µm (~0.0005 inch.), for accurate setting and measuring of spring length. The operator can select the spring length to be displayed in either millimetres or inches.
The motive power to drive the crosshead on the LTE-1000 Plus is provided by a micro-stepping motor driving twin preloaded ball screw acting on the crosshead. A stepping motor is used to provide accurate and positive location of the crosshead under computer control. This high level of positioning control ensures the spring is deflected to exactly the required test position prior to load measurement. Once in position the stepper motor cannot be back-wound by the spring. It is located positively awaiting the next computer command.
The preloaded ball screws are used both to minimise friction in the drive mechanism and to eliminate slack and backlash.
The machine is fitted with an interlocked polycarbonate guard, which inhibits the motor drive when not shut.
Computer Control/Data-logging System
All IST spring load testers come complete with an industrial computer that is used to control the operation of the tester and to analyse, display and store test data. A printer can be connected to the machine enabling rapid printout of results in the form of data and statistics. The printout is personalised with your own company details appearing at the head of each test certificate.
The IBM compatible computer is fitted with a hard disk, for storage of data and test sequence, CDRW, USB as well as a 1.4Mb floppy disk drive. The standard 17in. colour LCD monitor provides a clear and easily read display.
All manual operator controls and data input are entered via the keyboard. Apart from the on-off switch and the motor disable switch, no other user manual controls are present.
Loading frame deflection is compensated for by the controlling software, which provides the highest possible accuracy when measuring high rate springs.
The unique Windows based macro programming language - specifically designed for spring load testing applications provides the operator with total flexibility and enables the development of both simple and extremely complex test routines for any spring part, with speed and ease. The major features of the software are described below:
On line help systems simplify programming of the load tester.
All data and control inputs are made via the keyboard to call up menus and commands. Each current command key and its function is displayed on
the VDU to provide the operator with a constant monitor of the machine status.
Although designed primarily for automatic testing, the machine incorporates a manual control facility. This enables the operator to use the machine as a power assisted standard load tester that continuously displays load and length. This is a useful feature that allows a rapid one-off test to be carried out, avoiding the need to fully reset the machine. This facility can even be used in the middle of a long automatic run. The existing macro program and test data are automatically held in memory for recall once the machine is returned to the automatic mode.
Macro commands may be entered during manual operation to perform an automatic command e.g. GOTO LENGTH 50 moves the load platens to a distance of 50mm apart.
The spring and/or jig weight may be tarred by the operator at any time when the machine is stationary and within a macro. Tarring at the start of each automatic test on a new spring (compression and extension springs) is selectable within the macro language.
The length reading may be zeroed or pre-set at any crosshead position. This facility enables the operator to easily set the length display when spring jigs or hooks are being used. The length may also be zeroed or pre-set within the macro program.
The datum feature enables the platens or hooks to be zeroed/pre-set automatically.
- The software enables any combination of units to be used, such as kgf for the load with the spring length in inches.
When used in the automatic mode, the operator can set test positions as either a specified load or length. This means that within a single test cycle the machine can be set to measure and tolerance test loads at specified lengths or test lengths at specified loads or any combination of these.
Springs can be automatically prestressed / scragged to either a load or a length and at any step within the macro program. Prestressing can also be undertaken in the manual mode by simply typing the command via the keyboard.
Crosshead movement can be controlled in incremental units to enable deflections of load or length to be programmed, or absolute units for movement to a specified spring load or length.
The maximum crosshead speed can be set either within the macro program or in the manual mode.
- Flexible programming language enables automatic 100% measurement of:
- Free Length
- Solid length can be automatically measured for compression springs and is usually tested at 125% of the theoretical solid load
- Initial Tension (Extension Springs)
- Spring Load or Length at up to 50 test positions with tolerances can be recorded for any single test cycle
- Spring rate between any specified test positions can be measured whether they are consecutive or not
- Spring set down (loss of load or length)
All measured test parameters may be toleranced with max. and min. values. During a test, any measured parameter found to be outside the set tolerance band is indicated by the reading and associated tolerance being displayed in red on the VDU. The calculated Cpk, range, max, min, x, Std dev is continuously displayed against each toleranced test position for early warning of statistical capability problems.
Graphical displays of x and range control charts (for all data, sub grouped and ISO TS16949: 2002) histograms, full load/deflection and rate curves are also available within the standard software.
To enable rapid setting up of the machine for repeat jobs, the macro program for the test sequence can be stored on and retrieved from the hard disk. The macro program and measured data is readily identified by user-entered details such as part number, batch number and customer. A comprehensive search system is included to simplify recall of data and macro programs.
A macro can be password protected to stop unauthorised modification.
A spring counter is displayed on the screen to register the number of springs tested from a current batch.
Pause and Delay commands enable a test sequence to be halted for either a set time period or for operator acknowledgement. An alarm and message-to-screen command enable interaction between the machine and the operator during an automatic test.
During a test run the computer automatically backs up the current test data and macro program so that should a power failure occur the results up to that point will not be lost. On resumption of power the data and machine can be reset and testing continued.
Data can be received or sent to third party equipment via the RS232 port.
The printer (laser) and associated software enables the macro program, test data and statistical data to be printed out as a test certificate. Previously stored data may also be recalled and printed. This routine has the user-selectable option of printing out any or all of the following, the macro program, data or statistics.
A label printing system also enables the results of each test to be printed onto self-adhesive labels for individually identifying springs.
Option 1a/b (Rods for Buckling Springs)
When using a guide rod the upper platen must be removed and replaced with a platen incorporating a clearance hole to enable the rod to pass through it. IST offers a set of standard fixtures for this machine that provides rod sizes of 1 to 10mm (0.040inch to 0.375inch).
Fixtures for other sizes can be produced so that the rod / hole combination can be tailored to the spring being tested; these items are made to special order. Please contact IST for further information.
Option 2 (Increase Test Length)
The machine is supplied with a maximum gap between platens of 450mm. This may be increased in 50mm increments up to 750mm.
Option 3 (Addition of Measuring Device)
The software has the facility to link to external gauges e.g. verniers and digital micrometers. This allows the user to include dimensional measurement of the spring which cannot be listed by the load tester e.g. wire diameter, outside diameter, etc. into the load test results. This in turn allows statistical data to be calculated and the test certificates of the data produced. To enable the load tester to connect to these gauges an interface unit is required which allows the connection of upto 2 separate Mitutoya measurement gauges to the system. Gauges and cables may be supplied at extra cost, please contact IST for further information.
Option 4 (Connection to Network)
Multiple IST test machines may be connected to a network to allow for the sharing of files and data between test machines and other computers on the network. IST will supply the network card and software interface for this option. It is the client’s responsibility to supply a suitable server and software (or site licence) and to supply a connection point in close proximity to the machine. The network card supplied uses RJ45 connectors and has 10BaseT/100BaseTX configurations. It is highly recommended that the machines be connected to a Windows 2000/XP server to take advantage of its file storage facilities. Before ordering this option, please contact your agent / IST with details of your network to confirm its suitability for connection.
Option 5 (On Site Training)
The cost of the machine includes ½ day training at IST for up to 3 machine operators. If required IST can supply this training on site at the clients company. Please contact IST for further information.
Option 6 (On-site installation/commissioning and calibration.)
IST engineers can install, commission, calibrate and train operators at the customer’s works for the machines. Please contact IST to discuss requirements.
Load Range: 5-1000N (1.1-225lbf)
Load Resolution: 0.01N (0.002lbf)
Maximum Length: 450mm (18inch)
Length Resolution: 0.01mm (0.0005inch)
Repeatability and Accuracy on Load: to BS EN ISO 7500-1:2004: Grade 0.5
Repeatability and Accuracy on Length: ±0.03/300mm travel (±0.0015/10inch)
Platen Diameter: 125mm (5.0inch)
Crosshead Speed (max.): 25mm/sec (1.0 inch/sec)
Machine Dimensions (excluding computer & printer): 600 wide x 480 deep x 820 high mm (24 x 19 x 33 inch)
Machine Weight: 100kg (220lbf)
Power Requirements: 220-240v, 5amp, 50/60Hz
(To be specified on order) OR 105-115v, 10amp, 50/60Hz
Temperature Range: 10 - 35 Deg C
Relative Humidity: less 80% (non condensing)
The high precision of this machine will enable calibration to BS EN ISO 7500-1:2004: Grade 0.5. This must be carried out after installation at the customer works by an independent calibration company at the customer’s cost.
Calibration is accomplished via a specific routine in the operating software. Access to the routine to enable adjustment is only available via a security password system.