Fork lift truck speed control dependent upon fork elevation
First Claim
1. A speed control circuit for a lift truck which includes an operator adjustable speed control mechanism, lift forks mounted on an extendable lift fork mast continuously extendable between a lower and elevated positions, an electric truck drive motor, an electric motor power source, and a motor controller for controlling the application of power to said drive motor from said power source in response to a power control signal, comprising:
- speed selector means generating a speed selection signal in response to adjustment of said operator adjustable speed control mechanism,fork height sensor means providing a continuously variable fork height signal in dependence upon the relative elevated position to which said lift forks are raised,clamp circuit means, responsive to said speed selector means and to said fork height signal, for providing a speed control signal corresponding to said speed selection signal but having a maximum signal level determined by said fork height signal,speed sensor means providing a speed sensor signal related to the speed of said lift truck andsummer means, responsive to said clamp circuit means and to said speed sensor means, for comparing said speed control signal and said speed sensor signal to provide said power control signal to said motor controller in dependence upon the difference between said speed control signal and said speed sensor signal.
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Accused Products
Abstract
A speed control circuit is provided for a lift truck which is driven by an electric truck drive motor powered from a power source through a motor controller. The motor controller is responsive to a power control signal generated by summing a speed sensor signal, which is derived by comparing a tachometer signal with a speed selection signal. A fork height sensor provides a fork height signal which is used to limit the maximum level of the speed control signal. A safety circuit monitors operation of the speed control circuit and disconnects the circuit from the motor controller upon occurrence of a malfunction.
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Citations
10 Claims
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1. A speed control circuit for a lift truck which includes an operator adjustable speed control mechanism, lift forks mounted on an extendable lift fork mast continuously extendable between a lower and elevated positions, an electric truck drive motor, an electric motor power source, and a motor controller for controlling the application of power to said drive motor from said power source in response to a power control signal, comprising:
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speed selector means generating a speed selection signal in response to adjustment of said operator adjustable speed control mechanism, fork height sensor means providing a continuously variable fork height signal in dependence upon the relative elevated position to which said lift forks are raised, clamp circuit means, responsive to said speed selector means and to said fork height signal, for providing a speed control signal corresponding to said speed selection signal but having a maximum signal level determined by said fork height signal, speed sensor means providing a speed sensor signal related to the speed of said lift truck and summer means, responsive to said clamp circuit means and to said speed sensor means, for comparing said speed control signal and said speed sensor signal to provide said power control signal to said motor controller in dependence upon the difference between said speed control signal and said speed sensor signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification