Keypad Scanner help!

Hi,

I am new to VHDL. I am having issues implementing a 3 x 3 keypad scanner. The similar technique I have used in C code but it doesn't seem to work with VHDL. I scan each column by putting a logic zero on it , then reading each row and looking for a zero which would tell me on which column and row the key has been pressed. In this case however, by using my code below, it only detects keys pressed in the final column (3, 6 , 9) as it is the last test in the process. Could someone please tell me why this is wrong and suggest a proper way to do this. I appreciate your help. Thanks alot in advance.

------------------------------------------------------------------
ENTITY KeypadScanner IS
PORT ( clock_50 : IN STD_LOGIC ;
       LED : OUT STD_LOGIC_VECTOR (7 DOWNTO 0);
         Keypad_write : OUT STD_LOGIC_VECTOR (3 DOWNTO 0);
         Keypad_read : IN STD_LOGIC_VECTOR (3 DOWNTO 0)
         );
END KeypadScanner;
-------------------------------------------------------------------
ARCHITECTURE behaviour of KeypadScanner IS
SIGNAL delay : INTEGER:= 1000;
BEGIN
PROCESS (clock_50)
BEGIN
    
    Keypad_write <= "0111" after 10000 ns; --put logic zero on 1st column and scan the rows
    If (Keypad_read = "0111" ) THEN
        LED<= "00000001";
    ELSIf (Keypad_read = "1011") THEN
        LED<= "00000100";
    ELSIf (Keypad_read = "1101") THEN
        LED<= "00000111";
    END IF;
        
    Keypad_write <= "1011" after 10000 ns;--put logic zero on 2nd column and scan the rows
    If (Keypad_read = "0111") THEN
        LED<= "00000010";
    ELSIf (Keypad_read = "1011") THEN
        LED<= "00000101";
    ELSIf (Keypad_read = "1101") THEN
        LED<= "00001000";
    END IF;
    
    Keypad_write <= "1101" after 10000 ns;--put logic zero on 3rd column and scan the rows
    If (Keypad_read = "0111") THEN
        LED<= "00000011";
    ELSIf (Keypad_read = "1011") THEN
        LED<= "00000110";
    ELSIf (Keypad_read = "1101") THEN
        LED<= "00001001";
    END IF;
    
    
END PROCESS;
END behaviour;