Elevator car load measurement system and method for determining a load of an elevator car

A method for determining a load of an elevator car utilizing a plurality of force sensors that are connected together in a daisy chain, the method comprising the steps of:

• measuring forces exerted by the elevator car on the force sensors;
• generating by each of the force sensors a frequency signal with a square-wave form, wherein a frequency of the frequency signal is proportional to the force measured by the force sensor;
• receiving at each of the force sensors, except at a first one of the force sensors in the daisy chain, an output signal generated from a previous one of the force sensors in the daisy chain;
• each of the force sensors, except the first force sensor, adding the output signal received from the previous force sensor to the frequency signal generated thereby to generate a frequency sum signal as the output signal generated by it;
• a last one of the force sensors in the daisy chain forwarding the frequency sum signal to a controller;
• determining the load of the elevator car utilizing the controller based on the frequency sum signal forwarded to the controller;
• and
• when one of the force sensors detects a malfunction, generating a set error frequency signal from the one force sensor and substituting the set error frequency signal for the frequency signal to generate the frequency sum signal.

An elevator car load measurement system for determining a load of an elevator car, the elevator car load measurement system comprising:

• a plurality of force sensors connected together in a daisy chain including a first force sensor connected to one end of the daisy chain and a last force sensor connected to an opposite end of the daisy chain;
• a controller connected to the last force sensor for determining the load of the elevator car;
• wherein each of the force sensors measures a force exerted thereon by the elevator car and generates a frequency signal with a square-wave form, wherein a frequency of the frequency signal is proportional to the measured force;
• wherein a first force sensor generates the frequency signal as a first frequency signal and sends the first frequency signal to a second force sensor in the daisy chain, wherein the second force sensor adds the first frequency signal with a second frequency signal being the frequency signal generated by the second force sensor to generate a frequency sum signal and sends the frequency sum signal to a next one of the force sensors in the daisy chain;
• wherein each of the force sensors connected between the second force sensor and the controller adds the frequency sum signal received from an adjacent one of the force sensors in the daisy chain with the frequency signal generated by it to generate a new frequency sum signal;
• wherein the last force sensor forwards the new frequency sum signal generated by it to the controller for controlling the elevator car;
• and
• wherein each of the force sensors generates a set error frequency signal in response to detecting a malfunction of the force sensor, wherein each of the force sensors receiving the set error frequency signal from another of the force sensors does not add the set error frequency signal to generate the frequency sum signal or the new frequency sum signal, and wherein each of the force sensors receiving the set error frequency signal generates the set error frequency signal in place of the new frequency sum signal.