Radio controlled safety stop system for forklift trucks

• US 4,849,735 A
• Filed: 06/02/1987
• Issued: 07/18/1989
• Est. Priority Date: 06/02/1987
• Status: Expired due to Term

• Current Assignee: Kirtley James M
• Original Assignee: James M. Kirtley
• Inventors: Lamb, Kevin S., Kirtley, James M.
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US07/057,380
• Time in Patent Office: 777 Days
• Field of Search: 340/539, 340/901, 340/904, 340/988, 340/52 H, 340/61, 180/271, 49/13, 49/14
• US Class Current: 340/539.1
• CPC Class Codes: B66F 17/003 for fork-lift trucks

Abstract

Presented is a radio controlled safety stop system for forklift trucks including a transmitter mounted above a doorway in a warehouse or other building in such a way that a radio signal is continuously transmitted by the transmitter when the door is closed in a pattern such that the signal strength of the radio signal at a predetermined far distance from the door is detectably weaker than the radio signal that is detectable at a predetermined near distance from the door. Mounted on the forklift truck and provided with an appropriate antenna to detect the signals being transmitted, is a radio receiver which detects the radio signal when the forklift truck moves into the far distance zone included by the relatively weak radio signal, and which then functions to activate an alarm to warn the driver that he is approaching a danger zone. If the driver disregards the alarm and proceeds closer to the point of danger, say to the predetermined near distance limit at which the radio signal is more intense, the radio receiver on the forklift truck detects this second level of radio signal strength and responds by disabling the ignition system of the forklift truck.

Claims

1. In combination with a forklift truck having a motor for driving the truck and an electrical ignition system which enables operation of the truck motor when energized and interrupts operation of the truck when deenergized, a radio control system selectively operable to automatically sound an alarm to enable the operator of the forklift truck to take remedial action when the forklift truck approaches a predetermined restricted area, comprising:

(a) a radio transmitter mounted to transmit radio signals to define said restricted are within an "envelope" of radio signal;

(b) a radio receiver mounted on said forklift truck and having an antenna adapted to detect said transmitted radio signals prior to said forklift truck penetrating said "envelope" of radio signals and including means responsive to detection of said radio signal prior to penetration of said "envelope" to "enable" the sounding of an alarm;

(c) first means cooperatively related to said radio receiver and responsive to said "envelope" of radio signals after said alarm has been enabled for activating an audible alarm to warn the operator of the forklift truck when said forklift truck penetrates said "envelope" of radio signals and receives relatively weak radio signals whereby the operator of the forklift truck may take remedial action after the forklift truck has entered said restricted area; and

(d) second means cooperatively related to said radio receiver and responsive to relatively strong radio signals after activation of said audible alarm for automatically disabling the electrical ignition system of the forklift truck if the operator has not taken remedial action.

2. The combination according to claim 1, in which said transmitted radio signal is encoded with identifiable data, and said radio receiver includes a data decoder arranged to decode a stream of data received from said transmitter whereby a forklift truck including a data decoder responsive to said identifiable data is prevented by said second means from farther entering said restricted area.

3. The combination according to claim 1, in which said second means includes signal level detecting means for automatically deenergizing the ignition system of the forklift truck when the forklift truck progresses a predetermined distance beyond its position when said alarm is activated.

4. The combination according to claim 1, in which said transmitter includes a data encoder for selective encoding of a multiplicity of identifiable data codes in said transmitted radio signal at a data rate of approximately 420 baud, an operational amplifier which functions as a buffer for data, a voltage-variable capacitance diode the capacitance of which varies as the voltage applied thereacross, a crystal resonant at a predetermined base frequency which is shifted slightly by the variance of capacitance in said diode, an oscillator adapted to be frequency modulated by said data to produce a signal frequency of 106 MHz, means for multiplying the signal to produce a signal having a frequency of 318 MHz, a bandpass filter for receiving and filtering the 318 MHz signal, an amplifier for receiving the filtered 318 MHz signal, a second bandpass filter for receiving and filtering the amplified 318 MHz signal, and a resistive matching network for receiving and passing the transmitted radio signal to the transmitter antenna.

5. The combination according to claim 1, in which said transmitted radio signal is encoded with identifiable data, and said receiver includes an antenna for receiving said transmitted encoded radio signal, a signal mixer, means for channelling said received signal at a frequency of 318 MHz to said signal mixer, a local oscillator adapted to generate a signal having a frequency of 307.3 MHz, means for channelling said 307.3 MHz, signal to said mixer whereby the 10.7 Mhz differential of the 318 MHz signal and the 307.3 MHz signal is output from said mixer, means for receiving and demodulating said 10.7 MHz signal, comparator means for receiving the 10.7 Mhz signal from said demodulator to determine the signal strength thereof between two different levels thereof, a data decoder adapted to receive said signal from said demodulator, and means for receiving valid data from said decoder and signal strength data from said comparator, whereby an alarm is caused to sound when valid data and a predetermined low level of signal strength are received and said ignition is interrupted when valid data and a predetermined high level of signal strength are received.

6. In combination with a forklift truck having a motor for driving the truck and an electrical ignition system which enables operation of the truck motor when energized and interrupts operation of the truck when deenergized, a radio control system selectively operable to automatically sound an alarm when the forklift truck approaches a predetermined restricted area, comprising:

(a) a radio transmitter mounted to define said restricted area within an "envelope" of radio signals;

(b) a radio receiver mounted on said forklift truck and having an antenna adapted to detect said transmitted radio signal prior to said forklift truck penetrating said "envelope" of radio signals;

(c) means in said radio receiver for detecting variations in the signal strength of said transmitted radio signal correlated to the distance relationship of said forklift truck with said restricted area defined by said "envelope" of radio signals;

p1 (d) means operatively associated with said radio receiver to sound an audible alarm when said means for detecting the transmitted radio signal detects a weak signal upon penetration of said "envelope" of signals;

(e) means operatively associated with said radio receiver for interrupting the ignition system of the forklift truck when said means for detecting said transmitted radio signal detects a predetermined relatively stronger radio signal as the forklift truck penetrates farther into the "envelope" of radio signals

(f) said transmitter being mounted in close proximity to a doorway and a door associated with said doorway of a building in which said forklift truck is operative and being energized to transmit a radio signal when said door is closed; and

(g) said "envelope" of radio signals defining a predetermined area around said door, whereby said "envelope" of radio signals must necessarily be penetrated to reach said closed door.