<PAGE>
 
                                                                     EXHIBIT 3.6

                                                          FEDERAL IDENTIFICATION
                                                          NO. 04-2495703
                                                              -----------------

                       The Commonwealth of Massachusetts
                            William Francis Galvin
                         Secretary of the Commonwealth
             One Ashburton Place, Boston, Massachusetts 02108-1512


                             ARTICLES OF AMENDMENT
                   (General Laws, Chapter 156B, Section 72)
 
We,     Mitchell G. Tyson                 , *President
   --------------------------------------
and      Robert L. Birnbaum               , *Assistant Clerk,
   --------------------------------------
 
of                  PRI Automation, Inc.                             ,
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                          (Exact name of corporation)

located at:      805 Middlesex Turnpike, Billerica, MA 01821         ,
           ----------------------------------------------------------
               (Street address of corporation in Massachusetts)
 
certify that these Articles of Amendment affecting articles numbered:
 
         3
--------------------------------------------------------------------------------
         (Number those articles 1, 2, 3, 4, 5, and/or 6 being amended)
 
of the Articles of Organization were duly adopted at a meeting held on April 
22, 1997, by vote of

<TABLE> 
<S>                        <C>                            <C>          <C>  
  5,130,035      shares of       Common             of    7,408,399    shares outstanding,
---------------            ----------------------        -----------  -------------------------
                        (type, class & series, if any)
 
                 shares of                          of                 shares outstanding, and   
---------------            ----------------------         -----------  ------------------------- 
                        (type, class & series, if any)                                           
 
                 shares of                          of                 shares outstanding.
---------------            ----------------------         -----------  ------------------------- 
                        (type, class & series, if any)                                           
</TABLE>

/1/**being at least a majority of each type, class or series outstanding and
entitled to vote thereon:

*Delete the inapplicable words.            **Delete the inapplicable clause.
/1/ For amendments adopted pursuant to Chapter 156B, Section 70.
/2/ For amendments adopted pursuant to Chapter 156B, Section 71.

Note: If the space provided under any article or item on this form is
insufficient, additions shall be set forth on one side only of separate 8 1/2 x
11 sheets of paper with a left margin of at least 1 inch.  Additions to more
than one article may be made on a single sheet so long as each article requiring
each addition is clearly indicated.
<PAGE>
 
To change the number of shares and the par value (if any) of any type, class or
series of stock which the corporation is authorized to issue, fill in the
following:

The total presently authorized is:
<TABLE>
<CAPTION>
 
 
--------------------------------------------------------------------------------
       WITHOUT PAR VALUE STOCKS                   WITH PAR VALUE STOCKS
--------------------------------------------------------------------------------
 
           TYPE              NUMBER OF        TYPE         NUMBER OF      PAR
                               SHARES                       SHARES       VALUE
--------------------------------------------------------------------------------
<S>                          <C>         <C>             <C>            <C>
Common:                                  Common:            12,000,000      $.01
--------------------------------------------------------------------------------
 
--------------------------------------------------------------------------------
Preferred:                               Preferred:            400,000      $.01
--------------------------------------------------------------------------------
 
--------------------------------------------------------------------------------
</TABLE>

Change the total authorized to:

<TABLE>
<CAPTION>
 
 
 
       WITHOUT PAR VALUE STOCKS             WITH PAR VALUE STOCKS
--------------------------------------------------------------------------------
           TYPE               NUMBER OF        TYPE        NUMBER OF      PAR
                               SHARES                       SHARES       VALUE
--------------------------------------------------------------------------------
<S>                          <C>         <C>             <C>            <C>
Common:                                  Common:            24,000,000      $.01
--------------------------------------------------------------------------------
 
--------------------------------------------------------------------------------
Preferred:                               Preferred:            400,000      $.01
--------------------------------------------------------------------------------
 
--------------------------------------------------------------------------------
</TABLE>
<PAGE>
 
The foregoing amendment(s) will become effective when these Articles of
Amendment are filed in accordance with General Laws, Chapter 156B, Section 6
unless these articles specify, in accordance with the vote adopting the
amendment, a later effective date not more than thirty days after such filing,
in which event the amendment will become effective on such later date.

Later effective date:                                              .
                     ----------------------------------------------

SIGNED UNDER THE PENALTIES OF PERJURY THIS     22     day of   April,   19 97.
                                           -----------       -----------  ---

/s/ Mitchell G. Tyson         , *President
-----------------------------

/s/ Robert L. Birnbaum        , *Assistant Clerk. 
----------------------------- 

*Delete the inapplicable words.
<PAGE>
 
                       THE COMMONWEALTH OF MASSACHUSETTS

                             ARTICLES OF AMENDMENT
                    (GENERAL LAWS, CHAPTER 156B, SECTION 72)

================================================================================

I hereby approve the within Articles of Amendment, and the filing fee
in the amount of $___________ having been paid, said article is deemed to have 
been filed with me this ________ day of __________________________, 19_____.



Effective date:____________________________________________________



                             WILLIAM FRANCIS GALVIN
                         Secretary of the Commonwealth



                         TO BE FILLED IN BY CORPORATION
                      Photocopy of document to be sent to:


Robert L. Birnbaum, Esq.
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Foley, Hoag & Eliot LLP
One Post Office Square
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Boston, MA 02109
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