Sensor module ensures optimum battery utilisation

Some of the components and assembly tools used in the constructions of planes, trains or wind turbines can weigh up to 100ton. Despite this high weight and the sometimes bulky sizes, these loads need to be flexibly transported and precisely manoeuvred within a production hall. Alongside cranes, manufacturers also use heavy-duty vehicles as mobile platforms for internal transport.

These mobile platforms make it possible to move these barely transportable loads horizontally without the need to make structural adjustments to the production halls, as would be the case with cranes. Furthermore, the mobile platforms can also be moved flexibly and precisely in any direction between the various working positions and workstations. This reduces the spatial requirements for logistical processes, freeing up more space for production.

KUKA's omniMove platform stands out thanks to its ability to perfectly manoeuvre heavy loads in any direction and rotate them on the spot. "The omniMove makes it possible to move heavy parts very precisely in limited space, with 360° flexibility and a positioning accuracy of ± 2mm", explains Paul Wyszynski, Developer, KUKA Robote. "In the lifting platform variant, the omniMove can move in the millimetre range, even when the platform is raised. This is used when painting airliners, for example."

The platform is also called upon to transport gas turbines the size of a house, moving them between the individual production areas or to the testing area. The size, width and length of modular platform system are freely scalable and it can be combined with additional vehicles to form tandem or tridem configurations. This makes it possible to transport loads the size of an entire aircraft fuselage. The platform can be operated via remote control, optical tracking, or fully autonomously with laser scanners.

The omniMove's electrical drive is extremely efficient and quiet, even when used for long periods. The model KoM UTV-2 E375, for example, achieves a minimum operating duration of four hours. For technical and economic reasons, it is important that the available energy in a heavy-duty vehicle can always be used efficiently. This is why the lead gel batteries fitted as standard in the omniMove use current and voltage sensors based on sensor modules from Isabellenhütte, which are among the best in shunt-based current measurement technology.

Only by determining the current and voltage as precisely as possible is it possible to get a reliable picture of battery function, such as the state of charge, state of health, or the ability of the battery to fulfil a certain requirement such as start capability (state of function). "These measurement values can then be used to control the flow of energy in the battery, improve charging times and cycles, and lengthen the service life of the battery", confirms Jens Hartmann, Sales Director ISAscale, Isabellenhütte. The high utilisation of the omniMove batteries is achieved by precisely measuring the battery capacity.

KUKA uses the IVT Modular sensor module from Isabellenhütte to measure the current and voltage values in the omniMove vehicles. Isabellenhütte modified this tried-and-tested IVT sensor module to enable individual configuration with freely selectable modules. This means it can be adjusted at short notice to fit customer requirements. "Standardising the modular functions saves time when producing the sensor modules selected individually by the customer", explains Jens Hartmann. "That has a positive impact on development costs.

Customers can choose from the following components: insulation, excess current detection, hardware and software trigger, current measurement range, voltage measurement channels, interfaces and input voltage. For input voltage, the IVT Modular can be configured with 5V with regulated supply, or with 5 to 16V or 9 to 40V with unregulated supply. Galvanically separated insulation is possible for high voltages up to 800V. A hardware trigger is also available.This is an extra pin that makes it possible to start the measurement series with an external trigger.

An additional software trigger is included in the internal software, and is implemented in every module. There are five staged current measurement ranges: from ±100A at a resolution of 3mA to ±2,500A at a resolution of 186mA. The IVT Modular has three voltage measurement channels for a measurement range of up to 800V. The three voltage inputs can be configured to monitor three further potentials in the system.

The main factor that convinced KUKA to use the IVT modular in the battery system of its mobile platforms was the configurability with a CAN interface. "Before the sensors from Isabellenhütte, we used sensors that only had a series interface. That made it harder to evaluate the data, because the evaluation instruments we used had to be heavily adapted", says Paul Wyszynski. Another function of the IVT is the overvoltage detection for both positive and negative currents, which flow when charging or discharging the battery, for example. The threshold value and a hysteresis can be set via the software.

"When we decided on Isabellenhütte, it was also important for us to have a sensor that measures extremely precisely." Prior to using the IVT Modular, current measurements were made based on Hall sensors with a precision of just over 1 amp. In contrast, measurement using the Isabellenhütte sensor module is based on shunt technology. The precision for measuring voltage and current is also very high across the entire potential temperature range and under all environmental conditions.

The initial measurement precision of the IVT is 0.1 or 0.5% across the entire temperature range. Dissipation is low thanks to the extremely low resistance values of 5 to 285μΩ. The Isabellenhütte shunts are virtually drift free in the temperature range between -40° and +85°C, making them almost immune to temperature influences.

The IVT has further features in addition to the selectable modules. A bootloader can be used to install new firmware in order to gain new functions, for example. The diagnosis provides information about the sensor's area of application. While in use, it saves values such as maximum voltage, current and temperature, as well as the operating hours that can be used for statistical evaluations.

KUKA's omniMove vehicles have been fitted with the sensor module as standard ever since the IVT Modular was first implemented. The sensor module sends current and voltage data cyclically to the central computer via the CAN interface. The computer in the omniMove uses this data and the specific curves for the batteries to calculate the capacity every 100ms. It can determine, for example, whether there is sufficient energy for the current task. "If not, there is a corresponding reaction. An alarm is triggered on the vehicle and both the operator and higher-level control are informed", explains Paul Wyszynski.

The recorded data is evaluated using a logic that is suitable for the batteries used in the omniMove. This is because the chemical reactions within a battery are never linear, but depend on variables such as the ambient temperature, the level of current drain or the age of the battery. Paul Wyszynski explains: "Each of the drives on our omniMove platforms has a battery unit consisting of eight high-capacity battery boxes. Were any unused capacities to arise here, it would have significant consequences for our vehicles. That is why it is essential to be able to precisely determine the flow of energy in the batteries."