Better driving thanks to PME
Kühne + Vogel have complete faith in the benefits of the PME measuring amplifier system
The Kühne + Vogel company, based in Roth near Nuremberg and employing just 100 people, has been producing tailor-made solutions in the equipment-building and special machine-building sector for 30 years. A branch in Nuremberg concerns itself with tool-making and services such as factory maintenance. Most of their customers are based in Southern Germany, but their equipment is used all over the world.
Completele test-rigs for automotive suppliers
Kühne + Vogel offer their customers a complete equipment package from a single source. Examples include assembly and test rigs for suppliers in the automotive sector. Applications include testing window mechanisms, seats, air conditioning equipment, steering and hydraulics. They attach great importance to user-friendliness. Even for customised solutions, Kühne + Vogel use industry-standard systems from well-known manufacturers.
Ensuring the quality and operating comfort of car seats
For testing seat mountings and even complete car seats, Kühne + Vogel have already developed and produced a number of machines for famous automotive suppliers. The deciding quality criterion for user comfort in a car seat is the amount of force and torque that the driver and co-driver have to apply in order to adjust the seat. The equipment described below automatically captures, logs and analyses these adjustment forces. Previously, measurement data was determined using slip-ring free torque transducers and IGMD industry-standard torque measuring amplifiers from HBM (Fig. 1).
Fig1: Adjusting the rake of a seat squab. The test rig measures the amount of force required.
Wear-free – the HBM T34 torque transducer
T34 torque transducers work with a non-contacting data transfer system and therefore need neither slip-rings nor additional bearings between the rotor and the stator. This ensures freedom from wear and totally maintenance-free operation.
Data acquisition with an IPC
The output signal from the transducer shaft is a frequency signal which is unaffected by interference (10±5kHz) and which the rugged IGMD measuring amplifier converts into an analogue 0 to ±10V signal. The resulting measurement data is then gathered, displayed and analysed in a powerful industry-standard PC (IPC). The strict test conditions and limited time available for testing require one measured value to be captured every millisecond. With this in mind, an IPC with a measurement card that works independently of the operating system is used.
A new generation of test-rigs using the PME measuring amplifier
In a newly developed test-rig (Fig. 2) the forces required to adjust the rake of the driver's and co-driver's seat squabs must also be measured and analysed. The position of the seat squab and hand wheel are determined with the aid of an absolute angle of rotation transducer. DC servomotors are used for making adjustments. A T34 torque transducer is still used to measure the torque. As can be seen from the illustration, the test rig has a dual structure so that both the driver's and co-driver's seat can be tested in a single workstation. Using the new test-rig, measurement time is now only some 9 seconds and the cycle time is around 24 seconds. For such an advanced piece of equipment only the latest amplifier technology would suffice, and the decision was taken to use the industry- standard PME measuring amplifier system from HBM.
Fig 2. Test Rig using the latest advanced technology.
Advantages with PME
Using the new PME modules is not only more cost-effective but also gives the user a significant improvement over conventional analogue technology using IGMD. The assembly is simpler to fit on the standard rails in the control cabinet (Fig.3), minimal wiring is needed thanks to the plus-in screw terminals, an onsite display is provided in case a service visit is ever needed, and there is even a digital bus lin over CANopen and/or Profibus DP.
Fig.3. Controller for PME modules and servo power unit using a Siemens PLC and Profibus DP interface
Advantages of the PME system over the previous solution
- Digital signal conditioning, therefore 100% reproducible
- Integrated display and control panel for on-the-spot service
- Bus link over CANopen and Profibus DP for communication with PLC and PC
- Scalable analogue output (0 to ±10V or 0/4 to 20 mA selected by switch)
- Additional functions such as filtering, taring, limit values and digital I/Os (24 V PLC level) included as standard Industry-standard design – EMC compliant aluminium die-cast enclosure, electrically isolated 24 V supply
- Industry-standard design – EMC compliant aluminium die-cast enclosure, electrically isolated 24 V supply
The PME Setup Toolkit
It has also proven beneficial to use the PME Setup Toolkit for entering settings and parameters. This Setup Toolkit includes not only a Windows Setup Program but also an adapter for converting a parallel interface to CANopen and a cable for connecting the PC and module. Using this Toolkit provides an easy, quick and reliable way of assigning parameters to all PME modules. All the settings can then be saved to a diskette or hard disk and, in the event of a service requirement, the parameters can be downloaded to another module in the shortest possible time.
Although all relevant measurement data and all digital I/O signals can be transmitted over Profibus DP, subsequent data processing is still carried out in analogue mode in the case in question. The reasons for this can be found in the design adopted for the hardware and software of existing equipment and the special characteristics of the data analysis required. One measured value has to be imported per degree, so that the angular velocity amounts to 1°/ms. So far these requirements can only be fulfilled by using an IPC with a data entry card which is independent of the operating system. The graph shown here (Fig. 4) shows a typical analysis:
Fig.4: Typical plot showing torque and angle rotation
Profibus DP - the benefits
Even so, Profibus DP carries out some important tasks. These include such things as balancing the zero point before starting measurement or switching between four possible parameter sets, and transmitting errors at the transducer or in the amplifier module.
These features guarantee the highest possible level of accuracy and process reliability in ever operating mode. All these properties of the equipment designed and produced by Kühne + Vogel are very highly valued. By using the full PME product line from HBM, measurement technology can be integrated simply and cost-effectively into innovative automation processes. The trendsetting design of the PME product family sets new standards for integrating measurement technology with control engineering.