Patent ID: 8162083

Claim:
A crawler device comprising: a device body having a pair of left and right main crawlers, each of the main crawlers including an endless belt; a pair of left and right auxiliary crawlers extending in a straight line, each of the auxiliary crawlers including another endless belt and connected to a corresponding one of the main crawlers through a common sprocket, thereby synchronously driven with the corresponding main crawler; a tilt sensor for detecting a tilt angle of the device body in a front-rear direction; and a controller for controlling an angle of the auxiliary crawler with respect to the main crawler; wherein each of the pair of main crawlers has an inner side plate and an outer side plate; each of the pair of auxiliary crawlers has an inner side plate and an outer side plate; each of the auxiliary crawlers is connected to only one of opposite end portions of the corresponding main crawler opposing in a direction of travel of the corresponding main crawler and is disposed outside of the corresponding main crawler; a support having a cylindrical configuration is fixed to the inner side plate at the one of opposite end portions of the each of the main crawlers; the common sprocket is rotatably supported at an outer periphery of the support; an actuator is received in and fixed to the each support, an output shaft of the actuator being fixed to the outer side plate of the corresponding auxiliary crawler so that the pair of auxiliary crawlers can be rotated independently of each other over the entire angular range; a maximum overall length of the crawler device is the length of the crawler device when the main crawler and the auxiliary crawler are arranged in alignment with each other; a minimum overall length of the crawler device is equal to the length of the main crawler or the auxiliary crawler when the main crawler and the auxiliary crawler are positioned to overlap each other; before the device body ascends a step or stairs with the auxiliary crawler positioned backward, the controller controls the actuator to bring the auxiliary crawler into a preparatory state in which the auxiliary crawler is freely rotatable with respect to the main crawler or the auxiliary crawler is maintained in a rotated position above a line extending longitudinally from the main crawler; and when the main crawler starts ascending the step or stairs and the tilt angle of the device body detected by the tilt sensor reaches or exceeds a first threshold angle, the controller controls the actuator to cause the auxiliary crawler to be rotated downward.