Position detector for fluid cylinder

An industrial vehicle comprising:

• an implement;
• a mast for moving the implement;
• and
• a position detector for detecting the position of the mast, wherein the position detector includes:
• a fluid cylinder for moving the mast, wherein the cylinder includes a piston, the piston being axially moved within a predetermined range by fluid pressure;
• an ultrasonic transceiver provided in the cylinder, the transceiver being located near one end of the cylinder and outside of the moving range of the piston, wherein the transceiver transmits an ultrasonic wave to a reflection surface of the piston through a fluid in response to an electrical signal, and wherein the transceiver receives the ultrasonic wave reflected by the piston and generates an electrical signal, which corresponds to the reflected wave;
• a reference position detector for detecting that the piston is at a predetermined reference position;
• and
• a computer for supplying an electrical transmit signal to the transceiver, which causes the transceiver to transmit an ultrasonic signal, and for receiving an electrical reception signal from the transceiver, wherein the computer computes a time value representing the time from when an ultrasonic wave is transmitted to when the reflected wave is received, wherein the computer computes a speed indication value that indicates the speed of the ultrasonic signal when the piston is at the reference position, and wherein the computer computes the current position of the piston based on the speed indication value and on a current reading of the time value thereby detecting the position of the implement, which corresponds to the piston position.

A fluid cylinder having a piston, the piston being axially moved within a predetermined range by fluid and the pressure of the fluid, the cylinder comprising:

• a transmitting element located in the fluid cylinder to transmit ultrasonic waves to a reflection surface of the piston;
• a receiving element located in the fluid cylinder, wherein the receiving element is separated from the transmitting element, and wherein the receiving element receives the ultrasonic waves reflected by the piston;
• and
• a case for supporting the transmitter element and the receiving element, and wherein the case, together with the transmitting and receiving elements, is removably attached to the fluid cylinder.

A position detector for a piston in a fluid cylinder, wherein the fluid cylinder is a tilt cylinder and the piston is moved within a predetermined range by fluid and the pressure of the fluid, the position detector comprising:

• a transmitting element provided in the cylinder, the transmitting element being located outside of the moving range of the piston, wherein the transmitting element transmits an ultrasonic wave to a reflection surface of the piston through a fluid in response to an electrical signal;
• a receiving element located in the fluid cylinder, the receiving element being located outside of the moving range of the piston, wherein the receiving element is separated from the transmitting element, and wherein the receiving element receives the ultrasonic waves reflected by the piston and generates an electrical signal, which corresponds to the reflected wave;
• and
• a computer for supplying and electrical signal to the transmitting element to cause the transmitting element to transmit an ultrasonic wave, wherein the computer receives the electrical signal corresponding to the reflected wave from the receiving element, wherein the computer computes a distance detection value, which is a function of the travel time from when an ultrasonic wave is transmitted to when the reflected wave is received.

An industrial vehicle comprising:

• an implement;
• a mast for moving the implement;
• a position detector for detecting the position of the mast;
• a fluid cylinder for moving the mast, wherein the fluid cylinder comprises a tilt cylinder for inclining the mast, and wherein the fluid cylinder includes a piston, the piston being moved within a predetermined range by fluid pressure,
• a transmitting element provided in the cylinder, the transmitting element being located outside of the moving range of the piston, wherein the transmitting element transmits an ultrasonic wave to a reflection surface of the piston through a fluid in response to an electrical signal;
• a receiving element located in the fluid cylinder, the receiving element being located outside of the moving range of the piston, wherein the receiving element is separated from the transmitting element, and wherein the receiving element receives the ultrasonic waves reflected by the piston and generates an electrical signal, which corresponds to the reflected wave;
• and
• a computer for supplying and electrical signal to the transmitting element to cause the transmitting element to transmit an ultrasonic wave, wherein the computer receives the electrical signal corresponding to the reflected wave from the receiving element, wherein the computer computes a distance detection value, which is a function of the travel time from when an ultrasonic wave is transmitted to when the reflected wave is received.

A method for detecting the position of a piston in a fluid cylinder including:

• periodically transmitting an ultrasonic signal from a fixed position to the piston through the fluid;
• receiving the reflected ultrasonic signal;
• measuring time from when the ultrasonic signal is transmitted to when the reflected ultrasonic signal is received;
• judging that the piston is at a reference position, wherein the reference position is at a predetermined distance from the fixed position;
• computing a speed indication value that indicates the speed of the ultrasonic signal based on the measured time and the reference position when the piston is at the reference position;
• and
• computing the current position of the piston based on the speed indication value and a current reading of the measured time.

A method for detecting the position of a piston in a fluid cylinder including:

• periodically transmitting an ultrasonic signal from a first location to the piston through the fluid;
• receiving the reflected ultrasonic signal at a second location, wherein the first location is spaced from the second location;
• measuring time from when the ultrasonic signal is transmitted to when the reflected ultrasonic signal is received;
• judging that the piston is at a reference position, wherein the reference position is at a predetermined distance from the first location and second location;
• computing a speed indication value that indicates the speed of the ultrasonic signal based on the measured time and the reference position when the piston is at the reference position;
• and
• calculating the current position of the piston based on the speed indication value and a current reading of the measured time.