Photoelectric switch

A photoelectric switch, comprising:

• a projection head having a semiconductor laser as a light projecting device that projects a sensed light toward a sensing area;
• a reception head having a light receiving device for receiving a light from the sensing area of the light projecting device;
• a controller having a controlling portion provided separately from the projection head, for controlling a light projected from the light projecting device and also executing a sensing operation based on a quantity of received light of the light receiving device;
• and
• a head cable for connecting electrically the projection head and the controller;
• wherein the projection head includes
• a monitoring light receiving device for receiving a part of a light that the light projecting device emits, and
• a projected light quantity controlling device for executing a control such that a monitor signal obtained by the monitoring light receiving device is kept constant to maintain a quantity of projected light of the light projecting device at a predetermined value, and
• the controlling portion of the controller senses an abnormality of the projection head based on the monitor signal obtained from the monitoring light receiving device to be monitored via the head cable, and stops the light projected from the light projecting device.

A photoelectric switch, comprising:

• a projection head having a light projecting device for projecting a sensed light to a sensing area;
• a controller having a controlling portion provided separately from the projection head, for controlling a light projected from the light projecting device and executing a sensing operation based on sensing information of a light receiving device that receives a light from the sensing area of the light projecting device;
• and
• a head cable for connecting electrically the projection head and the controller;
• wherein the projection head includes
• a monitoring light receiving device for receiving a part of a light that the light projecting device emits,
• a projected light quantity controlling device for executing a control such that a monitor signal obtained by the monitoring light receiving device is kept constant to maintain a quantity of projected light of the light projecting device at a predetermined value,
• a light projecting device driving circuit for driving the light projecting device, the monitoring light receiving device, and the projected light quantity controlling device, and
• a monitor signal generating circuit for generating the monitor signal based on a signal that is sensed by the monitoring light receiving device,
• wherein the controller includes
• a monitor signal sensing circuit for sensing the monitor signal generated by the monitor signal generating circuit via the head cable,
• an abnormality deciding circuit for deciding the abnormality of the projection head based on information obtained by the monitor signal sensing circuit,
• a power controlling circuit for supplying a power to the projection head, and
• a timing controlling circuit for controlling a timing such that the power controlling circuit supplies a pulse power to the light projecting device driving circuit,
• wherein the controlling portion of the controller senses an abnormality of the projection head based on the monitor signal obtained from the monitoring light receiving device to be monitored via the head cable, and suppress the light projected from the light projecting device,
• wherein the monitoring light receiving device of the projection head includes a first monitoring light receiving device for receiving a part of the light emitted from the light projecting device and a second monitoring light receiving device for receiving another part of the light emitted from the light projecting device,
• wherein the projected light quantity controlling device of the projection head senses the abnormality of the projection head based on a first monitor signal obtained from the first monitoring light receiving device and suppresses the light projected from the light projecting device, and
• wherein the controlling portion of the controller senses the abnormality of the projection head based on a second monitor signal obtained from the second monitoring light receiving device to be monitored via the head cable, and suppresses the light projected from the light projecting device.