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New machine tests transmission bearings.

New machine tests transmission bearings

A new type of machine for automatic testing of bearings used in automatic transmissions has been developed for the auto industry by Superior Machine & Engineering Co, Marine City, MI. To control the machine for automatic operation, Superior chose an advanced programmable logic controller (PLC) that uses two parallel co-processors for rapid, thorough fault detection.

Already adopted as a standard by bearing manufacturers supplying General Motors Corp, the Model 182 spins bearing samples at speeds to 10,000 rpm, while applying axial and/or radial loads to 5000 lb. If required, the test chamber can be flooded with transmission fluid and pressurized.

The system uses a number of sensors to detect part failure. For instance, thermocouples monitor part temperature, which rises as a failure begins to occur. After receiving a signal from a thermocouple, normally the system stops the test. It may be continued, however, if a destructive test is being performed, in which case the system records the temperature rise.

"While the Model 182 was designed primarily to test transmission bearings, it can test many other types of bearings," says William L Sweet, Superior's general manager. This makes it useful not only for standard testing, but also for developmental work to qualify bearing suitability. By changing rotating speed, pressure, fluid, and other variables, a user can simulate the environment in which a bearing will operate.

During operation, the test sample is rotated at a specified rpm. At the same time, forces are applied to the bearing from an axial and/or radial direction in any of four modes. These are called the constant, cyclic, ramping, and ramp-and-hold modes.

If both axial and radial loads are applied, each can be in any of the four modes. This means the system can operate in any of 16 test modes.

In addition, there is a special probe mode. Here, test parameters for force and spindle rpm are automatically increased by 10 percent after each test phase is completed. These increases continue until either the bearing or machine reaches its limits.

High-speed control

The Model 182's PLC is a Siemens Simatic Model S5-135U. In its maximum configuration, this controller offers up to 128K words of memory, and 4000 analog or digital I/Os. Further, the S5-135U supports coprocessing, and can be connected to a local-area network (LAN).

Designated a very high speed controller, this PLC can be used for sequential and process control in dedicated operations, or as a multiprocessor system for simultaneous control of independent tasks.

For the bearing test machine, only two processors are used. Should the user decide to perform more complex data processing, however, a third processor can be added.

In its one rack, the PLC contains two processors, a video card to run a color monitor, three analog input cards, and a number of digital I/O cards. The analog inputs monitor axial and radial loads, deriving their signals from load cells.

The system also monitors torque required to operate the bearing under test. Other inputs measure temperatures derived from thermo-couples. Analog outputs control the drive speed and force applied on the bearing by means of a proportioning valve that controls hydraulic fluid.

An important feature of the test machine is a menu-driven operator communications station, which includes a keyboard and color monitor. All necessary procedures for conducting specified tests are presented on a color CRT. When delivered to a customer, the Model 182 has 32 test programs stored in control memory.

Key capabilities

According to Superior, one reason they standardized on Siemens PLCs is that they can accommodate a wide range of applications, from a few I/Os to thousands. In addition, these controllers offer coprocessing, structured programming, and networking.

Coprocessing deserves special attention, says Sweet. "In conventional PLCs, program logic is performed in essentially a sequential mode. That is, the PLC's central processing unit (CPU) stores process input samples in associated memory at the start of every cycle."

The same memory, he continues, may be shared over a common bus by other functions such as intelligent I/Os. The program compares the input samples to values stored originally, and produces outputs that are subsequently stored.

At the end of each cycle, output statuses are sent to their associated process (physical) outputs to produce desired actions. All these steps involve the same memory. Consequently, in large systems, processing may be relatively slow.

To overcome this and achieve high-speed processing, Superior specified parallel coprocessors. Two or more independent processors share a common memory, but each also has its own local memory. By dividing program logic into distributed, manageable tasks, and assigning them to multiple processors working in parallel, the system provides very high processing speed.

In a coprocessing operation, each CPU accesses a common bus to read input signals and set outputs. Since each CPU has its own memory (up to 36K words of 16 bits each), it processes its data and feeds the master CPU only the results of such processing. A coordinator processor manages CPU activity.

Function blocks

Structured programming, another major PLC feature, breaks up machine logic into discrete, manageable tasks. This means a program can be made up of sprecific function blocks instead of conventional, sequential steps. As a result, programming time can be shortened, and memory capacity is conserved.

A particularly useful benefit of structured programming in high-speed testing is in block transfers. With most conventional PLCs, block transfers are used to update analog input cards, because this is how they communicate with their intelligent modules. To perform a block transfer, a PLC must scan through the entire cycle, and then make the transfer.

"In the Simatic S5-135U, however, such updates can be performed on the spot, without the usual sequence delay of about 50 milliseconds," Sweet explains. "This instantaneous update of analog inputs lets the PLC observe every transient that occurs in the system during a test.

"For instance, hydraulic spikes that would be smoothed out by the scan delays in other PLCs can be fully detected. Capturing these spikes is very important."

A third significant feature of Siemens PLCs, he adds, is their capability of being interconnected on LANs. "In most cases, our bearing test machines are supplied for stand-alone service," Sweet says, "but come customers may want to connect a machine's PLC to other PLCs or to a host computer."

For full details on bearing test machines and other special machinery, write to: Superior Machine & Engineering Co, Marine City, MI 48039. For information on PLCs, write to: Siemens Corp, 186 Wood Ave South, Iselin, NJ 08830.

Top priority

Testing of completed cars on torture-test sites has been glamorized by the media, but testing of individual auto components and subsystems goes largely un-noticed. Sweet points out. "It is in this area that ingenuity by test sequence designers really comes out. Here lies the eventual success or failure of a completed car.

"With the extended warranties that auto manufacturers are offering, component testing is rapidly becoming a top priority in the overall auto manufacturing process."

PHOTO : Model 182 bearing test machine built by Superior Machine & Engineering Co. The control system, based on a Siemens Simatic Model S5-135U PLC, was designed by Jack Brenner (pictured).

PHOTO : A bearing sample being placed inside the Model 182's test chamber. This can be flooded with transmission fluid and pressurized.

PHOTO : Functional block diagram of Siemens Simatic Model S5-135U PLC as used on the Model 182. Two parallel coprocessors are provided; a third can be added readily.

PHOTO : Screen display for a test in progress. Shown are loads, speed, torque, temperatures, and reject limits. Also displayed are cycle time, number of cycles, and other data pertinent to the particular test.
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Title Annotation:includes related article
Publication:Tooling & Production
Date:Jan 1, 1990
Words:1277
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