An apparatus in a forklift for detecting the height of a fork in stages. Two sensors are arranged longitudinally on the mast. Each sensor includes a switch that has two states. The state of each switch can be changed by movement of the fork. Each switch is connected to input terminals of a controller. The signal at each input terminal changes between two levels in accordance with the state of a corresponding switch. A memory in the controller stores data that defines the relationship between ranges of movement of the fork, or zones, and the combination of the signals. The controller judges the height of the fork when the combination of signals corresponds to a combination that exists in the data. The controller judges that there is an abnormality when the combination does not exist in the data. This permits detection of malfunctioning switches and a cut and a short-circuited wiring.

An industrial lift truck with a load lifting device (15), a device (3, 9, 11) for moving the load lifting device (15) on the lift truck (1) having at least one element (7) that can move, together with the load lifting device (15), along an essentially straight guide (5), and with a position measuring device for monitoring the relative position to the guide (5) of the element (7) movable with the load lifting device (15). The position measuring device has at least one roller body (19) that is arranged on the element (7) that is movable with the load lifting device (15) such that it is capable of rotation and rolls along a path (21) running along the guide (5) when the element (7) moves, whereupon the roller body acts in combination with a sensor which transmits an electric signal as a function of the rotational movement of the roller body to an analysis circuit which evaluates the signal to determine the position of the element (7) that is movable with the load lifting device (15), or the position of the load carrier (15), relative to the guide (5).

Transport system (2), comprising a controller, a drive motor and a safety switch (18) that is connected to a safety-related part (8, 10) of the transport system (2) and is able to distinguish between a safe state of the transport system (2) and an unsafe state of the transport system (2), where the safety switch is connected to the controller in order to interrupt the power to the drive motor in an unsafe state, characterized by the fact that the safety switch (18) is realized so that it is able to also detect a warning state in addition to the safe state and the unsafe state.

In accordance with a preferred embodiment of the present invention, an electronic safety system for elevators for preventing unsafe elevator operation has a central controller which monitors a variety of sensors, contacts, and switches over an electronic safety bus. A plurality of bus nodes are distributed throughout the elevator system and are in constant communication with the central controller over the safety bus. The bus nodes interface with sensors, switches, contacts, detectors, components, and other safety equipment of the elevator system at each location and provide status information back to the controller. The controller consists of a microprocessor board with an input/output port in communication with the safety bus and bus nodes. Upon sensing an unsafe condition, the controller sends control signals to an elevator control system and a drive and brake system to arrest the elevator car in a safe manner.

A drive control apparatus for a forklift. Based on the load state, it is determined whether to limit a maximum vehicle speed and an acceleration/deceleration during traveling of the forklift. Limitation contents regarding the maximum vehicle speed and the acceleration/deceleration is determined based on a determination result of whether to put the limitations. A speed of the engine is adjusted based on the determined limitation contents, thereby controlling driving of the forklift. When the determined limitation contents are changed, an acceleration/deceleration limitation value is selected from a plurality of acceleration/deceleration limitation values according to the pattern of the change of the limitation contents, and drive control related to the acceleration/deceleration is executed to limit the acceleration/deceleration of the forklift by using the selected acceleration/deceleration limitation value.