Electrophotographic image forming apparatus

A copying machine wherein a developing device is provided with a first sensor for detecting the toner density in a developer and a second sensor which is provided around a photosensitive drum for detecting the amount of deposited toner on a test pattern. The toner supply is controlled according to a result detected by the second sensor. When the toner density is judged high from a result detected by the first sensor, a developing bias voltage is set high by a computer, and when the toner density is judged low, the developing bias voltage is set low.

What is claimed is:

1. An electrophotographic image forming apparatus which forms an electrostatic latent image on an image carrier, develops the electrostatic latent image and transfers the developed image onto a sheet, the electrophotographic image forming apparatus comprising:

developing means for developing an electrostatic latent image which is formed on the image carrier;

first detecting means for detecting an amount of deposited toner on a test pattern which is formed on the image carrier;

toner supply control means for controlling the toner supply according to a result which is detected by the first detecting means;

second detecting means for detecting a toner density in a developer of the developing means; and

image forming condition changing means for changing an image forming condition by changing both a developing bias voltage and a charged voltage of the image carrier according to a result which is detected by the second detecting means.

2. An image forming apparatus as claimed in claim 1, wherein:

the toner supply control means compares the result which is detected by the first detecting means to a first standard density, and supplies toner when the detected result is lower than the first standard density; and

the image forming condition changing means compares a result which is detected by the second detecting means to a second standard density, and when the detected result is higher than the second standard density, the image forming condition is changed to increase a developing efficiency, and if the detected result is lower than the second standard density, the image density is changed to decrease a developing efficiency.

3. An image forming apparatus as claimed in claim 2, wherein when the result which is detected by the second detecting means is higher than the second standard density, the image forming condition is changed to increase the developing efficiency if the result which is detected by the first detecting means is lower than the first standard density, and when the result which is detected by the second detecting means is lower than the second standard density, the image forming condition is changed to decrease the developing efficiency if the result which is detected by the first detecting means is higher than the first standard density.

4. The image forming apparatus as claimed in claim 3, wherein the second standard density includes a range of density values.

5. The image forming apparatus as claimed in claim 4, wherein the second standard density includes a range of density values.

6. The image forming apparatus as claimed in claim 3, wherein the first standard density includes a range of density values.

7. The image forming apparatus as claimed in claim 2, wherein the first standard density includes a range of density values.

8. The image forming apparatus as claimed in claim 7, wherein the second standard density includes a range of density values.

9. The image forming apparatus as claimed in claim 2, wherein the second standard density includes a range of density values.

10. An image forming apparatus as claimed in claim 1, wherein the image forming condition changing means changes a .gamma. correction when the image forming condition is changed.

11. An electrophotographic image forming apparatus which forms an electrostatic latent image on an image carrier, develops the electrostatic latent image and transfers the developed image onto a sheet, the electrophotographic image forming apparatus comprising;

developing means for developing an electrostatic latent image which is formed on the image carrier;

first detecting means for detecting an amount of deposited toner on a test pattern which is formed on the image carrier;

toner supply control means for controlling the toner supply according to a result which is detected by the first detecting means;

second detecting means for detecting a toner density in a developer of the developing means; and

image forming condition changing means for changing an image forming condition according to a result which is detected by the second detecting means;

wherein the toner supply control means compares the result which is detected by the first detecting means and a first standard density, and supplies toner when the detected result is lower than the first standard density; and

the image forming condition changing means compares a result which is detected by the second detecting means and to a second standard density and when the result which is detected by the second detecting means is higher than the second standard density, the image forming condition is changed to increase the developing efficiency if the result which is detected by the first detecting means is lower than the first standard density, and when the result which is detected by the second detecting means is lower than the second standard density, the image forming condition is changed to decrease the developing efficiency if the result which is detected by the first detecting means is higher than the first standard density.

12. An image forming apparatus as claimed in claim 11, wherein the image forming condition to be changed is a developing bias voltage.

13. An image forming apparatus as claimed in claim 11, wherein the image forming condition to be changed is a charged voltage of the image carrier.

14. An image forming apparatus as claimed in claim 11, wherein the image forming condition to be changed is an amount of exposure of the image carrier.

15. The image forming apparatus as claimed in claim 11, wherein the first standard density includes a range of density values.

16. The image forming apparatus as claimed in claim 15, wherein the second standard density includes a range of density values.

17. The image forming apparatus as claimed in claim 1l, wherein the second standard density includes a range of density values.

18. An image forming apparatus as claimed in claim 11, wherein the image forming condition changing means changes a .gamma. correction when the image forming condition is changed.