CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($)	3 Months Ended		9 Months Ended
	Jan. 28, 2017	Jan. 30, 2016	Jan. 28, 2017	Jan. 30, 2016
Revenue:
Product sales	$ 36,746,000	$ 53,305,000	$ 81,833,000	$ 129,436,000
Contract services	16,417,000	14,255,000	57,664,000	49,905,000
Total revenue	53,163,000	67,560,000	139,497,000	179,341,000
Cost of sales:
Product sales	23,641,000	31,910,000	58,060,000	73,477,000
Contract services	10,171,000	9,025,000	37,986,000	31,683,000
Total cost of sales	33,812,000	40,935,000	96,046,000	105,160,000
Gross margin:
Product sales	13,105,000	21,395,000	23,773,000	55,959,000
Contract services	6,246,000	5,230,000	19,678,000	18,222,000
Total gross margin	19,351,000	26,625,000	43,451,000	74,181,000
Selling, general and administrative	12,788,000	13,313,000	39,838,000	43,302,000
Research and development	7,988,000	8,247,000	25,105,000	27,975,000
(Loss) income from operations	(1,425,000)	5,065,000	(21,492,000)	2,904,000
Other income (expense):
Interest income, net	390,000	181,000	1,162,000	673,000
Other expense, net	(46,000)	(215,000)	(476,000)	(2,796,000)
(Loss) income before income taxes	(1,081,000)	5,031,000	(20,806,000)	781,000
Provision (benefit) for income taxes	1,102,000	(1,133,000)	(2,809,000)	(2,821,000)
Net (loss) income	$ (2,183,000)	$ 6,164,000	$ (17,997,000)	$ 3,602,000
(Loss) earnings per share data:
Basic (in dollars per share)	$ (0.09)	$ 0.27	$ (0.78)	$ 0.16
Diluted (in dollars per share)	$ (0.09)	$ 0.27	$ (0.78)	$ 0.16
Weighted average shares outstanding:
Basic (in shares)	23,082,974	22,890,484	23,029,546	22,941,354
Diluted (in shares)	23,082,974	23,083,816	23,029,546	23,139,981